Volume 46,Issue 12,2017 Table of Contents
2017, 46(12):3577-3582.
Abstract:
A Co-based chalcogenide electrocatalyst has been synthesized by a facile one-step reaction of dodecacarbonyltetracobalt [Co4(CO)12] and elemental sulfur in 1, 6-hexanediol solvent under refluxing conditions. The characterizations of the synthesized compound are performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD shows the formation of cubic structure Co9S8 and SEM micrograph displays cauliflower-like surface morphologies. The catalyst has an open circuit potential (OCP) of 0.75 V (vs. NHE) and shows a promising catalytic activity for the oxygen reduction. The transfer coefficient and Tafel slope are calculated to be 0.50 and 119 mV in the potential region limited by charge transfer kinetics, respectively. The catalytic activity and the electrochemical stability of the catalyst have also been compared with a commercial Pt catalyst.
A Co-based chalcogenide electrocatalyst has been synthesized by a facile one-step reaction of dodecacarbonyltetracobalt [Co4(CO)12] and elemental sulfur in 1, 6-hexanediol solvent under refluxing conditions. The characterizations of the synthesized compound are performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD shows the formation of cubic structure Co9S8 and SEM micrograph displays cauliflower-like surface morphologies. The catalyst has an open circuit potential (OCP) of 0.75 V (vs. NHE) and shows a promising catalytic activity for the oxygen reduction. The transfer coefficient and Tafel slope are calculated to be 0.50 and 119 mV in the potential region limited by charge transfer kinetics, respectively. The catalytic activity and the electrochemical stability of the catalyst have also been compared with a commercial Pt catalyst.
2017, 46(12):3583-3588.
Abstract:
Spraying complex shape parts, it’s almost impossible to maintain a fixed angle between spray flame and substrate surface. Studying the effect of spray angle on coating characteristics is necessary. The present study investigates the influence of the concave radius size on the deposition rate. As feedstock material an agglomerated and sintered WC-10Co-4Cr powder with a size distribution of 15 - 45 μm was used. For the spray experiments the process parameters were held constant, while the radii were selected of 10, 15 and 25 mm in concave profile. It has been generally shown that the spray angle has a great effect on coating deposition rate. The reduction of the spray angle results in a decrease of the deposition rate. A significant degradation of the coating properties was found less to 30°. The relationship between the coating’s distribution and spray angle with different curvature radius was deduced.
Spraying complex shape parts, it’s almost impossible to maintain a fixed angle between spray flame and substrate surface. Studying the effect of spray angle on coating characteristics is necessary. The present study investigates the influence of the concave radius size on the deposition rate. As feedstock material an agglomerated and sintered WC-10Co-4Cr powder with a size distribution of 15 - 45 μm was used. For the spray experiments the process parameters were held constant, while the radii were selected of 10, 15 and 25 mm in concave profile. It has been generally shown that the spray angle has a great effect on coating deposition rate. The reduction of the spray angle results in a decrease of the deposition rate. A significant degradation of the coating properties was found less to 30°. The relationship between the coating’s distribution and spray angle with different curvature radius was deduced.
2017, 46(12):3589-3594.
Abstract:
Uniaxial tensile tests were carried out on T2 pure copper plate and H62 copper alloy subjected to identical heat treatment. The influences of different strain states on the damage degree of both materials were analyzed. It is found that the fracture and damage of T2 pure copper and H62 copper alloy were closely related to their microstructure under tensile loading. The shape factor of the studied materials showed a similar variation trend with increasing strain, while the shape factor of H62 copper alloy was larger than that of T2 pure copper and increased rapidly as compared to T2 pure copper. The relative shape factor of the studied materials showed very similar variation. H62 copper alloy entered the plastic deformation earlier than T2 pure copper, and hence its plastic deformation stage was shorter than that of T2 pure copper. Beyond a certain threshold, damage and deformation of H62 occurs faster than T2 pure copper. By virtue of exponential function, the normalized shape factor curves of the studied materials were fitted and the fitting equations were established, which revealed the relationship between the macroscopic deformation and microstructure of materials.
Uniaxial tensile tests were carried out on T2 pure copper plate and H62 copper alloy subjected to identical heat treatment. The influences of different strain states on the damage degree of both materials were analyzed. It is found that the fracture and damage of T2 pure copper and H62 copper alloy were closely related to their microstructure under tensile loading. The shape factor of the studied materials showed a similar variation trend with increasing strain, while the shape factor of H62 copper alloy was larger than that of T2 pure copper and increased rapidly as compared to T2 pure copper. The relative shape factor of the studied materials showed very similar variation. H62 copper alloy entered the plastic deformation earlier than T2 pure copper, and hence its plastic deformation stage was shorter than that of T2 pure copper. Beyond a certain threshold, damage and deformation of H62 occurs faster than T2 pure copper. By virtue of exponential function, the normalized shape factor curves of the studied materials were fitted and the fitting equations were established, which revealed the relationship between the macroscopic deformation and microstructure of materials.
2017, 46(12):3595-3600.
Abstract:
Oxide film rupture theory has become one of the most popular models to quantitatively predict the stress corrosion cracking (SCC) rate at crack tip of nickel-based alloys in high temperature and high pressure environments, and stress intensity factor has become an important parameter to measure the stress corrosion cracking rate. In order to further understand the fracture mechanism of the oxide film and the driving force of crack growth, film-induced stress intensity factor is proposed. To understand the effect of film-induced stress intensity factor on the micro-mechanical state at the tip of EAC, the stress-strain in the base metal at the EAC tip was simulated and discussed using a commercial finite element analysis code. And then the effect of film-induced stress intensity factor on Mises stress, equivalent plastic strain, tensile stress, tensile strain and tensile plastic strain gradient of crack tip was obtained, which provides a parameter to improve the quantitative predication accuracy of EAC growth rate of nickel-based alloys and austenitic stainless steels in the important structures of nuclear power plants. Therefore the oxide film rupture theory was improved.
Oxide film rupture theory has become one of the most popular models to quantitatively predict the stress corrosion cracking (SCC) rate at crack tip of nickel-based alloys in high temperature and high pressure environments, and stress intensity factor has become an important parameter to measure the stress corrosion cracking rate. In order to further understand the fracture mechanism of the oxide film and the driving force of crack growth, film-induced stress intensity factor is proposed. To understand the effect of film-induced stress intensity factor on the micro-mechanical state at the tip of EAC, the stress-strain in the base metal at the EAC tip was simulated and discussed using a commercial finite element analysis code. And then the effect of film-induced stress intensity factor on Mises stress, equivalent plastic strain, tensile stress, tensile strain and tensile plastic strain gradient of crack tip was obtained, which provides a parameter to improve the quantitative predication accuracy of EAC growth rate of nickel-based alloys and austenitic stainless steels in the important structures of nuclear power plants. Therefore the oxide film rupture theory was improved.
2017, 46(12):3601-3605.
Abstract:
Vanadium dioxide (VO2) undergoes a Mott metal-insulator transition (MIT) close to room temperature, and has been suggested as a candidate for use in smart window and adaptive infrared camouflage. Here we report the synthesis of uniform free-standing VO2 nanowires using a novel hydrothermal method. The synthetic nanowires have typical diameters of 150±30 nm and lengths of tens of micrometer. These VO2 nanowires exhibit high crystallinity and feature a pure monoclinic phase and composition characterized by X-ray diffraction, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy and selected area electron diffraction. Moreover, reversible phase transition properties of VO2 nanowires are monitored via differential scanning calorimetry, variable temperature X-ray diffraction and temperature-dependent Raman spectroscopy. The results show VO2 nanowires obtained exhibit a reversible phase transition with an endothermic phase transition at 65.2 °C and a narrow hysteresis width of 6.5 °C. These VO2 nanowires should provide promising materials for fundamental investigations of nanoscale metal-insulator transitions.
Vanadium dioxide (VO2) undergoes a Mott metal-insulator transition (MIT) close to room temperature, and has been suggested as a candidate for use in smart window and adaptive infrared camouflage. Here we report the synthesis of uniform free-standing VO2 nanowires using a novel hydrothermal method. The synthetic nanowires have typical diameters of 150±30 nm and lengths of tens of micrometer. These VO2 nanowires exhibit high crystallinity and feature a pure monoclinic phase and composition characterized by X-ray diffraction, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy and selected area electron diffraction. Moreover, reversible phase transition properties of VO2 nanowires are monitored via differential scanning calorimetry, variable temperature X-ray diffraction and temperature-dependent Raman spectroscopy. The results show VO2 nanowires obtained exhibit a reversible phase transition with an endothermic phase transition at 65.2 °C and a narrow hysteresis width of 6.5 °C. These VO2 nanowires should provide promising materials for fundamental investigations of nanoscale metal-insulator transitions.
2017, 46(12):3606-3612.
Abstract:
Ti(C,N,O) films were deposited on Si (100), 304 stainless steel by Filtered Cathodic Vacuum Arc (FCVA) using CO2 and N2 (with ratio of 1:1) as precusors. The effect of gas flow rate on the composition, phase structure and properties of films was investigated by XPS, XRD, Raman, SEM, Tribological Test and Electrochemical workstation. The contents of C and N increase obviously, while contents of O and Ti decrease slightly as the gas flow rate increasing from 10sccm to 50sccm. The contents of C and N decrease, while content of Ti increases slightly and content of O increases dramatically as the gas flow rates from 50sccm to 80sccm. The phase structure of Ti(C,N,O) films transformed from nc-Ti(C,N,O) nanocrystal structure to nc-Ti(C,N,O)/a-CNx nanocomposite structure, a-TiO2/a-CNx and N-doped a-TiO2/a-C nanocomposite structure as gas flow rate increasing from 10sccm to 80sccm. The N-doped a-TiO2/a-C nanocomposite showed the lowest friction coefficient. Both nc-Ti(C,N,O)/ a-CNx nanocomposite structure and N-doped a-TiO2/a-C nanocomposite structure showed good anticorrosion ability in Hanks balance solution.
Ti(C,N,O) films were deposited on Si (100), 304 stainless steel by Filtered Cathodic Vacuum Arc (FCVA) using CO2 and N2 (with ratio of 1:1) as precusors. The effect of gas flow rate on the composition, phase structure and properties of films was investigated by XPS, XRD, Raman, SEM, Tribological Test and Electrochemical workstation. The contents of C and N increase obviously, while contents of O and Ti decrease slightly as the gas flow rate increasing from 10sccm to 50sccm. The contents of C and N decrease, while content of Ti increases slightly and content of O increases dramatically as the gas flow rates from 50sccm to 80sccm. The phase structure of Ti(C,N,O) films transformed from nc-Ti(C,N,O) nanocrystal structure to nc-Ti(C,N,O)/a-CNx nanocomposite structure, a-TiO2/a-CNx and N-doped a-TiO2/a-C nanocomposite structure as gas flow rate increasing from 10sccm to 80sccm. The N-doped a-TiO2/a-C nanocomposite showed the lowest friction coefficient. Both nc-Ti(C,N,O)/ a-CNx nanocomposite structure and N-doped a-TiO2/a-C nanocomposite structure showed good anticorrosion ability in Hanks balance solution.
2017, 46(12):3613-3620.
Abstract:
In this paper, an electrical contact-high speed imaging experimental system is developed to study the basic characteristics and laws of molten bridges of AgSnO2 electrical contact material under different loads. On the one hand, the quantitative measurements are investigated by high speed imaging technology. On the other hand, the microstructure and element distribution on the surface of contacts are analyzed by SEM and EDS after molten bridges behavior. Results indicate that the evolution behavior of AgSnO2 contacts can be divided into three regimes: the initial melting period, a stable period and an unstable period during which it eventually ruptures. Molten bridges and arc can exist simultaneously in which there is some cooperation and competition relationship. The dimension of molten bridges of AgSnO2 contact material is micron scale (0.027-0.295 mm), the diameter of molten bridges increases with the increase of current and the length decreases with the increase of current. In the process of the evolution behavior of molten bridges, the feature of molten bridges can be divided into three types: the pier, follow by the cylindrical and the dumbbell. The morphology and element distribution of the contacts surface are changed by the behavior of molten bridges.
In this paper, an electrical contact-high speed imaging experimental system is developed to study the basic characteristics and laws of molten bridges of AgSnO2 electrical contact material under different loads. On the one hand, the quantitative measurements are investigated by high speed imaging technology. On the other hand, the microstructure and element distribution on the surface of contacts are analyzed by SEM and EDS after molten bridges behavior. Results indicate that the evolution behavior of AgSnO2 contacts can be divided into three regimes: the initial melting period, a stable period and an unstable period during which it eventually ruptures. Molten bridges and arc can exist simultaneously in which there is some cooperation and competition relationship. The dimension of molten bridges of AgSnO2 contact material is micron scale (0.027-0.295 mm), the diameter of molten bridges increases with the increase of current and the length decreases with the increase of current. In the process of the evolution behavior of molten bridges, the feature of molten bridges can be divided into three types: the pier, follow by the cylindrical and the dumbbell. The morphology and element distribution of the contacts surface are changed by the behavior of molten bridges.
2017, 46(12):3621-3625.
Abstract:
High entropy alloy (HEA) thin coatings have been deposited on steel substrate of a mixed alloy power made of high purity elemental aluminium, cobalt, chromium, copper, iron and nickel by electron beam evaporation and effect of the Al content of the coating on its structural, surface morphology and electrical properties were investigated. The results of X-ray diffraction (XRD) showed that coatings were typical dendrite and interdendrite structures with different aluminum contents. The coatings’ surface chemistry components were basically similar composition as originally designed alloys by electron probe micro-analyzer (EPMA). Atomic force microscopy (AFM) indicated that modified the surface of all coatings were very smooth and uniform. HEA coatings exhibited wide passive regions, which extended ＞700 mV in aqueous solutions of H2SO4 and NaCl. A large corrosion potential (-129 mV) and a small corrosion current density (≈2.2×10-6 A/cm2) clearly revealed that the corrosion resistance of the Al0.5FeCoCrNiCu coating was superior to that of the coatings.
High entropy alloy (HEA) thin coatings have been deposited on steel substrate of a mixed alloy power made of high purity elemental aluminium, cobalt, chromium, copper, iron and nickel by electron beam evaporation and effect of the Al content of the coating on its structural, surface morphology and electrical properties were investigated. The results of X-ray diffraction (XRD) showed that coatings were typical dendrite and interdendrite structures with different aluminum contents. The coatings’ surface chemistry components were basically similar composition as originally designed alloys by electron probe micro-analyzer (EPMA). Atomic force microscopy (AFM) indicated that modified the surface of all coatings were very smooth and uniform. HEA coatings exhibited wide passive regions, which extended ＞700 mV in aqueous solutions of H2SO4 and NaCl. A large corrosion potential (-129 mV) and a small corrosion current density (≈2.2×10-6 A/cm2) clearly revealed that the corrosion resistance of the Al0.5FeCoCrNiCu coating was superior to that of the coatings.
2017, 46(12):3626-3632.
Abstract:
The load-displacement curves, elastic modulus, indent morphology, nanohardness and elastic recovery of high purity tungsten single crystal were investigated by nanoindentation and scanning probe microscopy. W (111) crystal plane undergoes elastic deformation and plastic deformation during the loading-unloading process, and the load-displacement curve does not show discontinuity, which demonstrates that cracks and brittle fracture are not formed in the indents. Moreover, the pile-up behavior around indents reveals that tungsten single crystal has the low work hardening tend. The nanohardness and elastic modulus of tungsten single crystal were measured by continuous stiffness measurement (CSM), and a size effect on the nanohardness and elastic modulus of tungsten single crystal was observed, which decrease with the increase of indentation depth. The Nix-Gao model was employed to analyze the nanoindentation mechanical characteristics of tungsten single crystals, and the characteristic length(h*), the intrinsic hardness in the limit of infinite depth(H0) and size effect index(m) were calculated to be 1490nm, 6.79GPa and 0.18 respectively, which indicates that tungsten single crystal has a significant size effect when the indentation depth is below about 1490nm, and the size effect becomes more insignificant when indentation depth is above 1490nm.When the impression is deeper than 2450nm, the nanoindentation size effect on the hardness will disappear.
The load-displacement curves, elastic modulus, indent morphology, nanohardness and elastic recovery of high purity tungsten single crystal were investigated by nanoindentation and scanning probe microscopy. W (111) crystal plane undergoes elastic deformation and plastic deformation during the loading-unloading process, and the load-displacement curve does not show discontinuity, which demonstrates that cracks and brittle fracture are not formed in the indents. Moreover, the pile-up behavior around indents reveals that tungsten single crystal has the low work hardening tend. The nanohardness and elastic modulus of tungsten single crystal were measured by continuous stiffness measurement (CSM), and a size effect on the nanohardness and elastic modulus of tungsten single crystal was observed, which decrease with the increase of indentation depth. The Nix-Gao model was employed to analyze the nanoindentation mechanical characteristics of tungsten single crystals, and the characteristic length(h*), the intrinsic hardness in the limit of infinite depth(H0) and size effect index(m) were calculated to be 1490nm, 6.79GPa and 0.18 respectively, which indicates that tungsten single crystal has a significant size effect when the indentation depth is below about 1490nm, and the size effect becomes more insignificant when indentation depth is above 1490nm.When the impression is deeper than 2450nm, the nanoindentation size effect on the hardness will disappear.
2017, 46(12):3633-3638.
Abstract:
In current work, commercial cerium has been zone refined by induction heating in a cold crucible against the pollution from the crucible materials. A numerical model of solute redistribution during zone refining is integrated into the genetic algorithm (GA) to search after the optimum zone length in different zone passes for increasing the redistribution efficiency of solutes, and the effect of variable distribution coefficient on purification efficiency is also considered in model. The chemical analysis results after 15 zone passes have showed that the content of Fe and Ni at center of sample bar are reduced by 50% and 90%, and the major difference of these two solutes with close effective distribution coefficient is their initial content. The main difference of experimental results and calculation results is from the instability of shorter zone during later zone passes. Experimental and calculation results show that GA is powerful tool for looking for optimum of zone lengths in zone passes, but the stability should be maintained in experiment by effective method to promote smoothly mobility of solutes in molten zone; the initial content of solutes should be kept as low as possible for getting better purification effect.
In current work, commercial cerium has been zone refined by induction heating in a cold crucible against the pollution from the crucible materials. A numerical model of solute redistribution during zone refining is integrated into the genetic algorithm (GA) to search after the optimum zone length in different zone passes for increasing the redistribution efficiency of solutes, and the effect of variable distribution coefficient on purification efficiency is also considered in model. The chemical analysis results after 15 zone passes have showed that the content of Fe and Ni at center of sample bar are reduced by 50% and 90%, and the major difference of these two solutes with close effective distribution coefficient is their initial content. The main difference of experimental results and calculation results is from the instability of shorter zone during later zone passes. Experimental and calculation results show that GA is powerful tool for looking for optimum of zone lengths in zone passes, but the stability should be maintained in experiment by effective method to promote smoothly mobility of solutes in molten zone; the initial content of solutes should be kept as low as possible for getting better purification effect.
2017, 46(12):3639-3644.
Abstract:
Recently, fabrication techniques of ultrafine-grained (UFG) pure titanium have been investigated to achieve enhanced performance. This paper reveals the process and properties of bulk ultrafine-grained pure titanium by equal-channel angular pressing (ECAP), with the influence of experimental parameters. Special attention is given to the deformation mechanisms via dislocation slip and twinning during ECAP. It is demonstrated that the change of microstructure in UFG Ti leads to significant enhancement of mechanical properties. Some mixed results about corrosion resistance of UFG Ti indicate the further investigations necessary. Special emphasis is placed on the combination of ECAP and other treatments for improving overall properties. It is shown that significant enhancement has been made in UFG commercial-purity Ti after ECAP plus thermal-mechanical treatment, suggesting promising prospects of ECAP process for titanium alloys in various industries.
Recently, fabrication techniques of ultrafine-grained (UFG) pure titanium have been investigated to achieve enhanced performance. This paper reveals the process and properties of bulk ultrafine-grained pure titanium by equal-channel angular pressing (ECAP), with the influence of experimental parameters. Special attention is given to the deformation mechanisms via dislocation slip and twinning during ECAP. It is demonstrated that the change of microstructure in UFG Ti leads to significant enhancement of mechanical properties. Some mixed results about corrosion resistance of UFG Ti indicate the further investigations necessary. Special emphasis is placed on the combination of ECAP and other treatments for improving overall properties. It is shown that significant enhancement has been made in UFG commercial-purity Ti after ECAP plus thermal-mechanical treatment, suggesting promising prospects of ECAP process for titanium alloys in various industries.
2017, 46(12):3645-3650.
Abstract:
Successive deposition of uniform metal droplet is a new kind of 3D printing and rapid prototyping (RP) technology. This paper presents a systematic numerical investigation of the transient transport phenomenon during the overlap of successive aluminum droplets impinging onto a substrate surface. The physical mechanisms of the overlap process, including the bulk liquid, capillarity effects at the liquid-solid interface, heat transfer, and solidification, are identified and quantified numerically. The 3D models based on a volume of fluid (VOF) method were developed to investigate the successive deposition of molten metal droplets on a horizontally fixed aluminum substrate surface. The numerical models are validated with experiments. The comparison between numerical simulations and experimental findings shows a good agreement. The effects of various parameters such as impact velocity, substrate temperature, droplet diameters on the maximum spread factor during impacting and spreading with solidification of a molten droplet onto an aluminum surface under different parameters was studied. Based on the above research, a semi-quantitative relationship between external morphology and internal microstructure was proposed, which was further certified by investigating the piled overlap of successive droplets. This investigation is essential to implement effective process control in metal micro-droplet deposition manufacture.
Successive deposition of uniform metal droplet is a new kind of 3D printing and rapid prototyping (RP) technology. This paper presents a systematic numerical investigation of the transient transport phenomenon during the overlap of successive aluminum droplets impinging onto a substrate surface. The physical mechanisms of the overlap process, including the bulk liquid, capillarity effects at the liquid-solid interface, heat transfer, and solidification, are identified and quantified numerically. The 3D models based on a volume of fluid (VOF) method were developed to investigate the successive deposition of molten metal droplets on a horizontally fixed aluminum substrate surface. The numerical models are validated with experiments. The comparison between numerical simulations and experimental findings shows a good agreement. The effects of various parameters such as impact velocity, substrate temperature, droplet diameters on the maximum spread factor during impacting and spreading with solidification of a molten droplet onto an aluminum surface under different parameters was studied. Based on the above research, a semi-quantitative relationship between external morphology and internal microstructure was proposed, which was further certified by investigating the piled overlap of successive droplets. This investigation is essential to implement effective process control in metal micro-droplet deposition manufacture.
2017, 46(12):3651-3657.
Abstract:
In this study, the high frequency deflection scanning of vacuum electron beam technology (DSEB) with line by line scanning mode and no overlap was employed to treat with the surface of TC18 titanium alloy, for obtaining a homogeneous hardened surface layer. The purpose of this work was to investigate the effects of critical process parameters, including beam current, focus current and treatment times, on the microstructure, hardness and treated depth of the treatment area. The treated specimens were characterized by using SEM, Optical Microscope, and Vickers hardness tester. After treated by DSEB, the hardened surface layer is formed, which is mainly consisted of the acicular martensite, and the surface hardness of the treatment area is improved. Moreover, the microstructure of the hardened zone is homogeneous and has no obvious transition at the contact parts of two adjacent electron beams scanning. The depth of the hardened zone can be more than 200 μm and basically constant. These results show that DSEB is a very promising technological solution for the surface heat treatment of titanium alloy of large area and complex components.
In this study, the high frequency deflection scanning of vacuum electron beam technology (DSEB) with line by line scanning mode and no overlap was employed to treat with the surface of TC18 titanium alloy, for obtaining a homogeneous hardened surface layer. The purpose of this work was to investigate the effects of critical process parameters, including beam current, focus current and treatment times, on the microstructure, hardness and treated depth of the treatment area. The treated specimens were characterized by using SEM, Optical Microscope, and Vickers hardness tester. After treated by DSEB, the hardened surface layer is formed, which is mainly consisted of the acicular martensite, and the surface hardness of the treatment area is improved. Moreover, the microstructure of the hardened zone is homogeneous and has no obvious transition at the contact parts of two adjacent electron beams scanning. The depth of the hardened zone can be more than 200 μm and basically constant. These results show that DSEB is a very promising technological solution for the surface heat treatment of titanium alloy of large area and complex components.
2017, 46(12):3658-3662.
Abstract:
The effect of cathodic hydrogen evolution on coercivity and thermal stability had been investigated in sintered NdFeB magnets. The magnetic properties, phase structure and morphology were systematically studied by SQUID-VSM, DSC, XRD, TEM and SEM. After cathodic hydrogen evolution, The Hcj decreased from 13 to 12.1 kOe. The temperature coefficients α declined from -0.253 %/℃ to -0.3229 %/℃, and the β declined from -0.7518 %/℃ to -0.7738 %/℃. A mechanism was proposed to explain the results. In the process of cathodic hydrogen evolution, parts of the generated hydrogen atoms reacted with the Nd2Fe14B phase and Nd-rich phase, formed Nd2Fe14BHx and NdHx, respectively. The formation of NdHx caused a volume expansion. Which resulted in intergranular cracks and stress. X-ray diffraction and morphology characterization confirmed the presence of these defects. These defects would significantly promote the nucleation of reverse magnetic domains, and further declined the coercivity and thermal stability of magnets.
The effect of cathodic hydrogen evolution on coercivity and thermal stability had been investigated in sintered NdFeB magnets. The magnetic properties, phase structure and morphology were systematically studied by SQUID-VSM, DSC, XRD, TEM and SEM. After cathodic hydrogen evolution, The Hcj decreased from 13 to 12.1 kOe. The temperature coefficients α declined from -0.253 %/℃ to -0.3229 %/℃, and the β declined from -0.7518 %/℃ to -0.7738 %/℃. A mechanism was proposed to explain the results. In the process of cathodic hydrogen evolution, parts of the generated hydrogen atoms reacted with the Nd2Fe14B phase and Nd-rich phase, formed Nd2Fe14BHx and NdHx, respectively. The formation of NdHx caused a volume expansion. Which resulted in intergranular cracks and stress. X-ray diffraction and morphology characterization confirmed the presence of these defects. These defects would significantly promote the nucleation of reverse magnetic domains, and further declined the coercivity and thermal stability of magnets.
2017, 46(12):3663-3668.
Abstract:
A SiC/MoSi2-ZrB2 ceramic coating was prepared by a magnetron sputtering method on carbon/carbon composites to protect it against oxidation. The microstructure of the coating was investigated, and its oxidation behavior at 1273K and 1773 K in air was also studied. The as-received coating exhibited outstanding uniformity in thickness and presented columnar structure. The coated C/C composites performed a superior oxidation resistance, and the weight loss of the samples after oxidation at 1273K and 1773 K for 60min in oxygen containing environment was 5.6×10-2 g/cm2 and 6.3×10-2 g/cm2 , respectively.
A SiC/MoSi2-ZrB2 ceramic coating was prepared by a magnetron sputtering method on carbon/carbon composites to protect it against oxidation. The microstructure of the coating was investigated, and its oxidation behavior at 1273K and 1773 K in air was also studied. The as-received coating exhibited outstanding uniformity in thickness and presented columnar structure. The coated C/C composites performed a superior oxidation resistance, and the weight loss of the samples after oxidation at 1273K and 1773 K for 60min in oxygen containing environment was 5.6×10-2 g/cm2 and 6.3×10-2 g/cm2 , respectively.
2017, 46(12):3669-3674.
Abstract:
In this work, Ag/AgCl nanoparticles are immobilized onto the as-prepared CoFe2O4 fibers by a facile synthesis method. The amount of Ag/AgCl nanoparticles immobilized onto CoFe2O4 fibers can be tuned. The as-synthesized Ag/AgCl@CoFe2O4 composite fibers are characterized by XRD, FESEM and EM, and employed to degradate MO (Methyl Orange) dye in wastewater under visible light. The results show that AAC-4 fiber exhibits higher efficiency for the degradation of the MO dye under visible light illumination than other Ag/AgCl@CoFe2O4 composite fibers or pure Ag/AgCl sample, and the decolorizing efficiency of MO can research 98.2%. The immobilization of Ag/AgCl nanoparticles onto CoFe2O4 fiber promotes the enhancement of photocatalytic efficiency and stability.
In this work, Ag/AgCl nanoparticles are immobilized onto the as-prepared CoFe2O4 fibers by a facile synthesis method. The amount of Ag/AgCl nanoparticles immobilized onto CoFe2O4 fibers can be tuned. The as-synthesized Ag/AgCl@CoFe2O4 composite fibers are characterized by XRD, FESEM and EM, and employed to degradate MO (Methyl Orange) dye in wastewater under visible light. The results show that AAC-4 fiber exhibits higher efficiency for the degradation of the MO dye under visible light illumination than other Ag/AgCl@CoFe2O4 composite fibers or pure Ag/AgCl sample, and the decolorizing efficiency of MO can research 98.2%. The immobilization of Ag/AgCl nanoparticles onto CoFe2O4 fiber promotes the enhancement of photocatalytic efficiency and stability.
2017, 46(12):3675-3681.
Abstract:
Coarsening kinetics of Pb phase in a nanocomposite alloy produced by mechanical alloying in immiscible Al-Pb system and the influence of Cu addition on it have been studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that when annealing at 573, 623, 673 and 723 K for different times, the relation of average particle size of Pb phase in Al-Pb nanocomposite alloys to time obeys the cube law even though the size of the constituent phase is in the nanometer range. The coarsening activation energy of Pb phase is 84.80 kJ/mol, close to the grain boundary self-diffusion activation energy of Al matrix. This indicates that the coarsening of Pb phase is controlled by grain boundary diffusion. Adding Cu decreases the coarsening rate of Pb phase, primarily by reducing the interfacial energy through Cu segregation at the Al/Pb interface. The coarsening activation energy of Pb phase is increased by the addition of Cu.
Coarsening kinetics of Pb phase in a nanocomposite alloy produced by mechanical alloying in immiscible Al-Pb system and the influence of Cu addition on it have been studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that when annealing at 573, 623, 673 and 723 K for different times, the relation of average particle size of Pb phase in Al-Pb nanocomposite alloys to time obeys the cube law even though the size of the constituent phase is in the nanometer range. The coarsening activation energy of Pb phase is 84.80 kJ/mol, close to the grain boundary self-diffusion activation energy of Al matrix. This indicates that the coarsening of Pb phase is controlled by grain boundary diffusion. Adding Cu decreases the coarsening rate of Pb phase, primarily by reducing the interfacial energy through Cu segregation at the Al/Pb interface. The coarsening activation energy of Pb phase is increased by the addition of Cu.
2017, 46(12):3682-3687.
Abstract:
Laser shock processing without coating (LSPwC) is a novel surface treatment, which can effectively increase the fatigue strength of metal materials by introducing compressive residual stress and microstructural changes. The objective of this work is to improve the fatigue resistance of K24 nickel based alloy by LSPwC. Firstly, high cycle vibration fatigue experiment was adopted to verify the LSPwC strengthening effect. Compared to the untreated samples, the results of the vibration fatigue experiments showed that the fatigue strength of K24 alloy was enhanced and improved from 282MPa to 328MPa after LSPwC. Secondly, the effects of multiple impacts on mechanical properties and fatigue fracture morphologies were investigated, which were observed and measured by scan electron microscope (SEM), X-ray diffractometer and microhardness tester. The results indicated that residual stress presented compressive state on the superficial layer with about 150μm depth and the maximum value reaches -595MPa. The microhardness is about 526 HV0.5 with about 100 μm depth from the top surface after three impacts. The fracture observation indicated that the flatness area was larger in the FCI after LSPwC, meanwhile, the growth rate of fatigue crack was decreased. Lastly, the strengthening mechanism of LSPwC on the fatigue resistance was discussed based on the experimental results.
Laser shock processing without coating (LSPwC) is a novel surface treatment, which can effectively increase the fatigue strength of metal materials by introducing compressive residual stress and microstructural changes. The objective of this work is to improve the fatigue resistance of K24 nickel based alloy by LSPwC. Firstly, high cycle vibration fatigue experiment was adopted to verify the LSPwC strengthening effect. Compared to the untreated samples, the results of the vibration fatigue experiments showed that the fatigue strength of K24 alloy was enhanced and improved from 282MPa to 328MPa after LSPwC. Secondly, the effects of multiple impacts on mechanical properties and fatigue fracture morphologies were investigated, which were observed and measured by scan electron microscope (SEM), X-ray diffractometer and microhardness tester. The results indicated that residual stress presented compressive state on the superficial layer with about 150μm depth and the maximum value reaches -595MPa. The microhardness is about 526 HV0.5 with about 100 μm depth from the top surface after three impacts. The fracture observation indicated that the flatness area was larger in the FCI after LSPwC, meanwhile, the growth rate of fatigue crack was decreased. Lastly, the strengthening mechanism of LSPwC on the fatigue resistance was discussed based on the experimental results.
2017, 46(12):3688-3692.
Abstract:
Both sequential and co-deposition methods based on electroless plating method for preparation of PdAg membranes were investigated. The morphology, phase structure, compositional homogeneity and compactness of the membranes prepared by two methods were compared. Results showed that Pd-Ag co-depositions were dendritic, inhomogeneous, poor compactness, while multi layer sequential depositions were more homogeneous and compact. The multi layer sequential depositions were required higher temperature and longer time for annealing to form Pd-Ag alloy. The Pd particles size was decreased by alternate Ag layer and the surface of Pd-Ag membrane was more smooth.
Both sequential and co-deposition methods based on electroless plating method for preparation of PdAg membranes were investigated. The morphology, phase structure, compositional homogeneity and compactness of the membranes prepared by two methods were compared. Results showed that Pd-Ag co-depositions were dendritic, inhomogeneous, poor compactness, while multi layer sequential depositions were more homogeneous and compact. The multi layer sequential depositions were required higher temperature and longer time for annealing to form Pd-Ag alloy. The Pd particles size was decreased by alternate Ag layer and the surface of Pd-Ag membrane was more smooth.
2017, 46(12):3693-3698.
Abstract:
As the key material of components used in elevated temperature of gas turbines, the mechanism of delamination and failure of thermal barrier coatings (TBCs) under service conditions has been the hot spot of research for a long time. The influences of strain ranges and phase angles on the thermomechanical fatigue (TMF) properties of samples with thermal barrier coatingsTBCs were investigated in this paper. It was is shown that under the same phase angles, the TMF lifetime decreased decreases with the increase of strain ranges. Under the same strain range, the in-phase tests had have longer TMF lifetime than out-of-phase tests. In both samples, cracks were are initiated in thermally grown oxide (TGO) layer, and then propagated along the bond coat/ceramic top coat, forming the delamination cracks. When the delamination cracks connected with the segmentation cracks initiated in ceramic coat, the TBCs spalled. A TMF lifetime model concerning strain ranges and phase angles was is established, and an exponential law exists between TMF lifetime and the maximum stress
As the key material of components used in elevated temperature of gas turbines, the mechanism of delamination and failure of thermal barrier coatings (TBCs) under service conditions has been the hot spot of research for a long time. The influences of strain ranges and phase angles on the thermomechanical fatigue (TMF) properties of samples with thermal barrier coatingsTBCs were investigated in this paper. It was is shown that under the same phase angles, the TMF lifetime decreased decreases with the increase of strain ranges. Under the same strain range, the in-phase tests had have longer TMF lifetime than out-of-phase tests. In both samples, cracks were are initiated in thermally grown oxide (TGO) layer, and then propagated along the bond coat/ceramic top coat, forming the delamination cracks. When the delamination cracks connected with the segmentation cracks initiated in ceramic coat, the TBCs spalled. A TMF lifetime model concerning strain ranges and phase angles was is established, and an exponential law exists between TMF lifetime and the maximum stress
2017, 46(12):3699-3714.
Abstract:
Based on thermodynamic calculation Pandat software and PanNi database, thermodynamic phase equilibrium calculation method was employed to investigate the effect of alloying composition on precipitation behavior of equilibrium phases in a low Re-containing nickel-based single crystal superalloy DD6. Results indicate that the equilibrium phases consist of γ, γ′, μ, MC and M23C6, and the calculated results are in excellent agreement with the experimental results. The Al, Ta and Nb content mainly control the mass fraction of γ′ precipitates. With increase of Al, Ta and Nb content, the mass fraction of γ′ precipitates is significantly enhanced, the solution temperature of γ′ precipitates is obviously increased, and the liquid starting and finishing solidification temperature is gradually decreased. The C content determines the precipitation amount of MC and M23C6. Increment of C content results in more precipitation of carbides. The precipitation of μ phase is predominantly influenced by Re, W, Mo and Cr. With the increase of Re, W, Mo and Cr content, the initial precipitation temperature of μ phase is significantly enhanced, the maximum precipitation amount of μ phase is obviously increased, and the precipitation temperature range of μ phase is markedly extended.
Based on thermodynamic calculation Pandat software and PanNi database, thermodynamic phase equilibrium calculation method was employed to investigate the effect of alloying composition on precipitation behavior of equilibrium phases in a low Re-containing nickel-based single crystal superalloy DD6. Results indicate that the equilibrium phases consist of γ, γ′, μ, MC and M23C6, and the calculated results are in excellent agreement with the experimental results. The Al, Ta and Nb content mainly control the mass fraction of γ′ precipitates. With increase of Al, Ta and Nb content, the mass fraction of γ′ precipitates is significantly enhanced, the solution temperature of γ′ precipitates is obviously increased, and the liquid starting and finishing solidification temperature is gradually decreased. The C content determines the precipitation amount of MC and M23C6. Increment of C content results in more precipitation of carbides. The precipitation of μ phase is predominantly influenced by Re, W, Mo and Cr. With the increase of Re, W, Mo and Cr content, the initial precipitation temperature of μ phase is significantly enhanced, the maximum precipitation amount of μ phase is obviously increased, and the precipitation temperature range of μ phase is markedly extended.
2017, 46(12):3715-3720.
Abstract:
The structures and mechanical properties of a new super-high strength Al-Li alloy developed by this group were investigated. The alloy possessed excellent properties, of which the tensile strength was greater than 600 MPa, and the elongation higher than 10%. After T8 aging, the strengthening precipitates in both cold-rolled sheet with 2 mm thickness and hot-rolled plate with 10 mm thickness were T1(Al2CuLi) and q￠(Al2Cu), and their fraction and size were basically same in the two plates with different thickness. The strength of T8-aged plate with 10 mm thickness was 50~70 MPa higher than that the T8-aged sheet with 2 mm thickness. This strength enhancement was originated from the texture fraction after solution treatment. The volume fraction of the deformation texture in the solutionized hot-rolled plate with 10 mm thickness was much higher.
The structures and mechanical properties of a new super-high strength Al-Li alloy developed by this group were investigated. The alloy possessed excellent properties, of which the tensile strength was greater than 600 MPa, and the elongation higher than 10%. After T8 aging, the strengthening precipitates in both cold-rolled sheet with 2 mm thickness and hot-rolled plate with 10 mm thickness were T1(Al2CuLi) and q￠(Al2Cu), and their fraction and size were basically same in the two plates with different thickness. The strength of T8-aged plate with 10 mm thickness was 50~70 MPa higher than that the T8-aged sheet with 2 mm thickness. This strength enhancement was originated from the texture fraction after solution treatment. The volume fraction of the deformation texture in the solutionized hot-rolled plate with 10 mm thickness was much higher.
2017, 46(12):3721-3727.
Abstract:
In order to promote the shape adjustment method of aluminum alloy sheet using pulsed electromagnetic force to a mature process. An appropriative equipment was developed, which can satisfy the shape adjustment of sheets not larger than 1500mm×800mm×6mm. The effect of shape adjustment times on the shape and curvature radius of 2198-T3 aluminum alloy specimens were studied based on that equipment. A flat spiral coil was used to conduct the shape adjustment experiments of specimens in different action times of pulsed electromagnetic force. The results show that the original flat specimens present double curvature surface features after shape adjustment. Curvature radius decreases with the increase of shape adjustment times while deflection increases with it and reaches a saturation value.
In order to promote the shape adjustment method of aluminum alloy sheet using pulsed electromagnetic force to a mature process. An appropriative equipment was developed, which can satisfy the shape adjustment of sheets not larger than 1500mm×800mm×6mm. The effect of shape adjustment times on the shape and curvature radius of 2198-T3 aluminum alloy specimens were studied based on that equipment. A flat spiral coil was used to conduct the shape adjustment experiments of specimens in different action times of pulsed electromagnetic force. The results show that the original flat specimens present double curvature surface features after shape adjustment. Curvature radius decreases with the increase of shape adjustment times while deflection increases with it and reaches a saturation value.
2017, 46(12):3728-3732.
Abstract:
The influence of nature aging (NA) on the Portevin-Le Chatelive (PLC) effect was investigated via tension tests in solution treated 6061 Al alloy. The yielding strength, the tensile strength, the critical strain and the serration period changed little in the NA time range of 0~1 h and then increased with increasing NA time. The serration amplitude decreased in the NA time range of 0~2 h and kept constant over 2 h. The precipitation sequence of the alloy suggests that the precipitates that can significantly strengthen the alloy formed after NA for 1 h and increased linearly with NA time. These precipitates inhibit the dislocation motion and result in shortening the waiting time. It is more difficult to produce the pinning process and thus the serration period and the critical strain increase. Moreover, the solute atoms gather to mobile dislocations by body diffusion rather than pipe diffusion in this alloy.
The influence of nature aging (NA) on the Portevin-Le Chatelive (PLC) effect was investigated via tension tests in solution treated 6061 Al alloy. The yielding strength, the tensile strength, the critical strain and the serration period changed little in the NA time range of 0~1 h and then increased with increasing NA time. The serration amplitude decreased in the NA time range of 0~2 h and kept constant over 2 h. The precipitation sequence of the alloy suggests that the precipitates that can significantly strengthen the alloy formed after NA for 1 h and increased linearly with NA time. These precipitates inhibit the dislocation motion and result in shortening the waiting time. It is more difficult to produce the pinning process and thus the serration period and the critical strain increase. Moreover, the solute atoms gather to mobile dislocations by body diffusion rather than pipe diffusion in this alloy.
25 High temperature deformation properties and the modification of constitutive model of Cu-Ag alloy
2017, 46(12):3733-3738.
Abstract:
The hot deformation behavior of Cu-6 wt.% Ag alloy was described by hot compression tests in the temperature range of 973～1123K and stain rates of 0.01～10s-1. The microstructure evolution of the alloy was investigated in this paper. The true stress-strain curves were studied to reveal the hot deformation mechanism of Cu-6 wt.% Ag alloy. A simple constitutive model was established. The Arrhenius equation and Z were quoted in this investigation to modified the model. The results show that the dynamic recovery, dynamic recrystallization occurred in Cu-6 wt.% Ag alloy during hot deformation. And twinning behavior was observed at the strain rates of 0.1s-1 and 1s-1 temperature of 1123K. This twining behavior result in sharp changing of flow stress. With the increase of flow stress, a valley of stress was observed directly. The modified model which integrated the influence of temperature, strain rates, strain on flow characteristic could predict the stress accurately and be compiled easily.
The hot deformation behavior of Cu-6 wt.% Ag alloy was described by hot compression tests in the temperature range of 973～1123K and stain rates of 0.01～10s-1. The microstructure evolution of the alloy was investigated in this paper. The true stress-strain curves were studied to reveal the hot deformation mechanism of Cu-6 wt.% Ag alloy. A simple constitutive model was established. The Arrhenius equation and Z were quoted in this investigation to modified the model. The results show that the dynamic recovery, dynamic recrystallization occurred in Cu-6 wt.% Ag alloy during hot deformation. And twinning behavior was observed at the strain rates of 0.1s-1 and 1s-1 temperature of 1123K. This twining behavior result in sharp changing of flow stress. With the increase of flow stress, a valley of stress was observed directly. The modified model which integrated the influence of temperature, strain rates, strain on flow characteristic could predict the stress accurately and be compiled easily.
26 The effect of pre-strain for the time-dependent springback of TA2 pure titanium at room temperature
2017, 46(12):3739-3743.
Abstract:
In order to reveal the effect of pre-strain for the time-dependent springback, the TA2 titanium sheets were drawn under different pre-strains by using the universal testing machine. The microstructures of the tested samples were both characterized by optical microscope and transmission electron microscope to infer the basis of the anelastic behavior. The results reveal that the time-dependent response of TA2 was obvious. The time-dependent-springback strain(TDSS) presented different exponential change laws in different plastic deformation zones. Both the TDSS and the amount of deformation twin increased as the pre-strain went up. The loading history and the interaction between dislocation and twin affected the TDSS and the relaxation-saturation time tIP.
In order to reveal the effect of pre-strain for the time-dependent springback, the TA2 titanium sheets were drawn under different pre-strains by using the universal testing machine. The microstructures of the tested samples were both characterized by optical microscope and transmission electron microscope to infer the basis of the anelastic behavior. The results reveal that the time-dependent response of TA2 was obvious. The time-dependent-springback strain(TDSS) presented different exponential change laws in different plastic deformation zones. Both the TDSS and the amount of deformation twin increased as the pre-strain went up. The loading history and the interaction between dislocation and twin affected the TDSS and the relaxation-saturation time tIP.
2017, 46(12):3744-3752.
Abstract:
2.5D woven fabric Cf/Al composites with 2.5D graphite fiber fabric as reinforcement and ZL301 as matrix alloy was fabricated by the vacuum pressure infiltration method. The density and microstructure of the composites, which were prepared with three fabric temperature level, was investigated. The crystal structure and composition of the interfacial product was revealed. The quasi-static tensile test and electron fractography was carried out to analyze the mechanical behavior of the composite along the warp and weft direction. The results indicated that the fabric structure can be maintained well, in which the fibers distributed in matrix alloy uniformly. With the increase of fabric temperature, the density of the composites was improved slightly while the relative amount of interfacial product, which was identified to be Al4C3 phase with rod shape, increased obviously, which lead to the reduction of mechanical properties both in warp and weft direction. The tensile strength in warp direction has been proven to be higher than that in weft direction. The stress-strain behavior in warp direction exhibit an significant nonlinear characteristic. The tensile deformation process both in warp and weft direction can be divided into three stages, i.e. the initial elastic deformation segment, the middle elastoplastic deformation segment and the final damage and fracture segment.
2.5D woven fabric Cf/Al composites with 2.5D graphite fiber fabric as reinforcement and ZL301 as matrix alloy was fabricated by the vacuum pressure infiltration method. The density and microstructure of the composites, which were prepared with three fabric temperature level, was investigated. The crystal structure and composition of the interfacial product was revealed. The quasi-static tensile test and electron fractography was carried out to analyze the mechanical behavior of the composite along the warp and weft direction. The results indicated that the fabric structure can be maintained well, in which the fibers distributed in matrix alloy uniformly. With the increase of fabric temperature, the density of the composites was improved slightly while the relative amount of interfacial product, which was identified to be Al4C3 phase with rod shape, increased obviously, which lead to the reduction of mechanical properties both in warp and weft direction. The tensile strength in warp direction has been proven to be higher than that in weft direction. The stress-strain behavior in warp direction exhibit an significant nonlinear characteristic. The tensile deformation process both in warp and weft direction can be divided into three stages, i.e. the initial elastic deformation segment, the middle elastoplastic deformation segment and the final damage and fracture segment.
2017, 46(12):3753-3759.
Abstract:
Single-crystal superalloys have been commonly used in modern advanced aero engines to produce high-pressure high-temperature turbine blades. In order to extend the lifetime of single-crystal turbine blades, repair of cracked and worn ones is of great interest. Laser Solid Forming (LSF) is a prospective technology that can be used to repair single-crystal blades. In this study, the microstructure of the as-deposited and heat-treated LSF single-crystal superalloy has been characterized through optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The as-deposited LSF sample showed a directionally solidified columnar dendrites growing almost parallel to the building direction. Between the dendrites, nearly round microporosity and blocky MC carbide particles were dispersed uniformly. TEM results indicated that many nano γ′ particles precipitated in γ matrix. In addition, during LSF deposition process, Stress was formed, which generated plenty of dislocations. During heat treatment, the LSF sample experienced fully recrystallization. The recrystallization grains were in different size, and twins were found in some recrystallized grains. Because the residual stress was fully released during heat treatment, the size and shape of γ′ precipitates in the recrystallized and un-recrystallized regions were similar to those in conventionally cast samples.
Single-crystal superalloys have been commonly used in modern advanced aero engines to produce high-pressure high-temperature turbine blades. In order to extend the lifetime of single-crystal turbine blades, repair of cracked and worn ones is of great interest. Laser Solid Forming (LSF) is a prospective technology that can be used to repair single-crystal blades. In this study, the microstructure of the as-deposited and heat-treated LSF single-crystal superalloy has been characterized through optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The as-deposited LSF sample showed a directionally solidified columnar dendrites growing almost parallel to the building direction. Between the dendrites, nearly round microporosity and blocky MC carbide particles were dispersed uniformly. TEM results indicated that many nano γ′ particles precipitated in γ matrix. In addition, during LSF deposition process, Stress was formed, which generated plenty of dislocations. During heat treatment, the LSF sample experienced fully recrystallization. The recrystallization grains were in different size, and twins were found in some recrystallized grains. Because the residual stress was fully released during heat treatment, the size and shape of γ′ precipitates in the recrystallized and un-recrystallized regions were similar to those in conventionally cast samples.
2017, 46(12):3760-3766.
Abstract:
Polycrystal plasticity model can reflect the material’s microstructure and various mechanical response, but it is too complecate for great computation. The phenomenological elasto-plastic constitutive model is relatively simple, as yet based on the additive decomposition of deformation rate tensor of phenomenological elasto-plastic constitutive model under the condition of large deformation will bring error. In this paper, the uniaxial tensile test process of pure aluminium and single crystal aluminium have carried on the calculation based on the polycrystal plasticity finite deformation elasto-plastic finite element method(CPFEM) and phenomenological elasto-plastic constitutive model, and compared the results of two models. It is researched that effect of calculation error about the deformation amount to the phenomenological elasto-plastic constitutive model. The results show that the stress-strain curve of pure aluminium calculated by phenomenological elasto-plastic constitutive model began to cause error when true strain exceeds 25.5%, and increases with increasing of strain. Polycrystal plasticity model reflect the anisotropy of deformation, texture and residual stress during large drformation of pure aluminium and single crystal aluminium.
Polycrystal plasticity model can reflect the material’s microstructure and various mechanical response, but it is too complecate for great computation. The phenomenological elasto-plastic constitutive model is relatively simple, as yet based on the additive decomposition of deformation rate tensor of phenomenological elasto-plastic constitutive model under the condition of large deformation will bring error. In this paper, the uniaxial tensile test process of pure aluminium and single crystal aluminium have carried on the calculation based on the polycrystal plasticity finite deformation elasto-plastic finite element method(CPFEM) and phenomenological elasto-plastic constitutive model, and compared the results of two models. It is researched that effect of calculation error about the deformation amount to the phenomenological elasto-plastic constitutive model. The results show that the stress-strain curve of pure aluminium calculated by phenomenological elasto-plastic constitutive model began to cause error when true strain exceeds 25.5%, and increases with increasing of strain. Polycrystal plasticity model reflect the anisotropy of deformation, texture and residual stress during large drformation of pure aluminium and single crystal aluminium.
2017, 46(12):3767-3772.
Abstract:
Ion chromatography and flame atomic absorption were used to analysis condensates collected in various temperature and slag. The results show that the main components of slag were FeCl2/FeCl3、NiCl2、CrCl2/CrCl3; the condensates were made up of CaCl2、HCl、HClO、H2O and metal chlorides. So the gas in reactor included Cl2、HCl、HClO、H2O、Ar and metal chlorides. The 1.0 L/min argon flow in reactor at 850 °C was simlated to find that it was very difficult to vent the HCl、HClO, et al., so these gases were reacted with reactor wall to produced metal chlorides, which led to seriously corroded, at the same time, HCl、HClO could impact in electrodeoxidation. Based on simlation and tail gas absorption experiment, argon flow increased to 5.0 L/min in 2 h of pre-electrolysis could effectively vent the HCl、HClO, et al. This improvement could enhance the electrolysis velocity and resolve the corrosion problem.
Ion chromatography and flame atomic absorption were used to analysis condensates collected in various temperature and slag. The results show that the main components of slag were FeCl2/FeCl3、NiCl2、CrCl2/CrCl3; the condensates were made up of CaCl2、HCl、HClO、H2O and metal chlorides. So the gas in reactor included Cl2、HCl、HClO、H2O、Ar and metal chlorides. The 1.0 L/min argon flow in reactor at 850 °C was simlated to find that it was very difficult to vent the HCl、HClO, et al., so these gases were reacted with reactor wall to produced metal chlorides, which led to seriously corroded, at the same time, HCl、HClO could impact in electrodeoxidation. Based on simlation and tail gas absorption experiment, argon flow increased to 5.0 L/min in 2 h of pre-electrolysis could effectively vent the HCl、HClO, et al. This improvement could enhance the electrolysis velocity and resolve the corrosion problem.
2017, 46(12):3773-3778.
Abstract:
:The change rule of friction and thermal properties of the alloy after thermal cycling was study by internal friction method combined with DSC, SEM and XRD. The change rule is that the alloy’s internal friction and DSC peak shift to high temperature when experiencing an increasing number of thermal cycles.The results show that this variation is attributed to the occurrence of Spinodal decomposition of the alloy, which formed Mn rich and Cu rich areas.We combine the mechanism of microstructure analyzed the internal friction peak .We calculated the activation energy(Ea) and the pre-exponential factor of relaxation (t0) of the low temperature side internal friction peak. Ea=0.66 eV(heating), Ea=0.74 eV(cooling),t0=1.4×10-15s(heating),t0=3.2×10-18s(cooling). Using the peak separation method to isolate the internal friction peak,which is caused bySmutual coupling of martensitic transformation and antiferromagnetic transition. According to the fitting results, the experimental phenomena can be explained reasonably.
:The change rule of friction and thermal properties of the alloy after thermal cycling was study by internal friction method combined with DSC, SEM and XRD. The change rule is that the alloy’s internal friction and DSC peak shift to high temperature when experiencing an increasing number of thermal cycles.The results show that this variation is attributed to the occurrence of Spinodal decomposition of the alloy, which formed Mn rich and Cu rich areas.We combine the mechanism of microstructure analyzed the internal friction peak .We calculated the activation energy(Ea) and the pre-exponential factor of relaxation (t0) of the low temperature side internal friction peak. Ea=0.66 eV(heating), Ea=0.74 eV(cooling),t0=1.4×10-15s(heating),t0=3.2×10-18s(cooling). Using the peak separation method to isolate the internal friction peak,which is caused bySmutual coupling of martensitic transformation and antiferromagnetic transition. According to the fitting results, the experimental phenomena can be explained reasonably.
2017, 46(12):3779-3784.
Abstract:
Choosing Al86Ni6Y4.5Co2La1.5 amorphous powder and adopting self-developed low-temperature supersonic spray system, the paper has prepared the aluminum-based metallic glass coating on ZM5 surface with good corrosion resistance, analyzed the pores’ types and causes in the coating, selected the X-ray three-dimensional imaging method for the determination of the coating’s porosity and the characterization of the pores’ geometry features, clarified the influence of pores on the corrosion behavior of the coating. The results show that the coating consists mainly of four types of conventional porosity defects，which are macro-type、layer-type、 microsphere-type and microscopic-type; The porosities are substantially less than 1% and have little change along the thickness direction, the pores are nearly spherical, and their average sizes are less than 10μm, especially about 5μm; different porosities in the coating are shown a wide range of self passivation interval, closer self corrosion potentials and positive correlation between the corrosion current densities and porosities. Individual special pores with the characteristics of large-size, through-type and at the border are the root cause of coating’s corrosion failure.
Choosing Al86Ni6Y4.5Co2La1.5 amorphous powder and adopting self-developed low-temperature supersonic spray system, the paper has prepared the aluminum-based metallic glass coating on ZM5 surface with good corrosion resistance, analyzed the pores’ types and causes in the coating, selected the X-ray three-dimensional imaging method for the determination of the coating’s porosity and the characterization of the pores’ geometry features, clarified the influence of pores on the corrosion behavior of the coating. The results show that the coating consists mainly of four types of conventional porosity defects，which are macro-type、layer-type、 microsphere-type and microscopic-type; The porosities are substantially less than 1% and have little change along the thickness direction, the pores are nearly spherical, and their average sizes are less than 10μm, especially about 5μm; different porosities in the coating are shown a wide range of self passivation interval, closer self corrosion potentials and positive correlation between the corrosion current densities and porosities. Individual special pores with the characteristics of large-size, through-type and at the border are the root cause of coating’s corrosion failure.
2017, 46(12):3785-3791.
Abstract:
In this paper, cobalt nanoparticles were deposited on the surface of graphene by electroless plating,first sensitization and then activation using stannous chloride and palladium chloride respectively. XRD and TEM results showed that the concentrations of cobalt precursor and reductant affected the structures and yield of cobalt crystals. Electromagnetic tests results showed that the increasing cobalt content and reduction of graphene both improved the conductivity of Co-RGO. Meanwhile, Co-RGO nanocomposites had excellent absorbing properties because of magnetic loss and dielectric loss by lots of interfaces. For instance, the bandwidth of reflection below -10dB for Co-RGO*1 during 1~18GHz was about 4GHz, and the reflection for Co-RGO*2 was below -23dB from 26.5 to 40 GHz.
In this paper, cobalt nanoparticles were deposited on the surface of graphene by electroless plating,first sensitization and then activation using stannous chloride and palladium chloride respectively. XRD and TEM results showed that the concentrations of cobalt precursor and reductant affected the structures and yield of cobalt crystals. Electromagnetic tests results showed that the increasing cobalt content and reduction of graphene both improved the conductivity of Co-RGO. Meanwhile, Co-RGO nanocomposites had excellent absorbing properties because of magnetic loss and dielectric loss by lots of interfaces. For instance, the bandwidth of reflection below -10dB for Co-RGO*1 during 1~18GHz was about 4GHz, and the reflection for Co-RGO*2 was below -23dB from 26.5 to 40 GHz.
2017, 46(12):3792-3798.
Abstract:
The micro crack propagation process and the fracture propagation mechanism of the single crystal γ-TiAl alloy of different crystallographic orientation on the microstructure has been studied. The prefabricated micro crack propagation process was simulated of three different crack crystallographic orientations of [100]、[110]and[111] for the single crystal γ-TiAl alloy by the molecular dynamics method. It showed that: The crack stress value is the minimum of [100] crystal orientation, and the crack intensity is the lowest so that it is easy to extend in the form of brittle cleavage extension. The stress has always focused on the crack tip in the process of the extension,and the system of stress decreasesed with time increased,The crack stress value of the [111] orientation is the largest. And the larger the crack strength, the more difficult to extend. The crack propagation process showed the obvious orientation effect. The micro crack extended by the way of crack tip slip dislocation and twin slip was formed on the crack tip. The stress distribution mainly focused on the crack tip and twinning plane in the process of extension, and decreased with time increased. The crack stress value of [110] orientation between two other crystallographic orientations,The Early extension is brittle cleavage extension and the crack tip atoms into chaos after expanded to a certain time and after the crack tip launch dislocation makes the crack tip passivation .As load continued, one the end of passivation crack tip sharp again and sub crack initiation which is not a flat surface with the main crack. At last,the main crack and the sub crack connected to form the micro cracks of step extension. The extension process showed some effect of orientation. The stress always focused on the crack tip, and decreased with time increased. The different crystallographic orientation has great influence to the micro crack propagation.
The micro crack propagation process and the fracture propagation mechanism of the single crystal γ-TiAl alloy of different crystallographic orientation on the microstructure has been studied. The prefabricated micro crack propagation process was simulated of three different crack crystallographic orientations of [100]、[110]and[111] for the single crystal γ-TiAl alloy by the molecular dynamics method. It showed that: The crack stress value is the minimum of [100] crystal orientation, and the crack intensity is the lowest so that it is easy to extend in the form of brittle cleavage extension. The stress has always focused on the crack tip in the process of the extension,and the system of stress decreasesed with time increased,The crack stress value of the [111] orientation is the largest. And the larger the crack strength, the more difficult to extend. The crack propagation process showed the obvious orientation effect. The micro crack extended by the way of crack tip slip dislocation and twin slip was formed on the crack tip. The stress distribution mainly focused on the crack tip and twinning plane in the process of extension, and decreased with time increased. The crack stress value of [110] orientation between two other crystallographic orientations,The Early extension is brittle cleavage extension and the crack tip atoms into chaos after expanded to a certain time and after the crack tip launch dislocation makes the crack tip passivation .As load continued, one the end of passivation crack tip sharp again and sub crack initiation which is not a flat surface with the main crack. At last,the main crack and the sub crack connected to form the micro cracks of step extension. The extension process showed some effect of orientation. The stress always focused on the crack tip, and decreased with time increased. The different crystallographic orientation has great influence to the micro crack propagation.
2017, 46(12):3799-3804.
Abstract:
The discontinuous and continuous precipitation behavior, and the interaction between them during the aging process in a Cu-20Ni-20Mn alloy have been investigated in the temperature range 573 K-698 K by scanning electron microscope (SEM), transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The results show that discontinuous precipitation is the predominant mechanism at 623 K and below, whereas both discontinuous and continuous precipitations occur when the temperature is higher than 673 K. The discontinuous precipitations with a lamellar mixed structure, consisting of alternate lamellae of matrix and NiMn phase, nucleate and grow preferentially on grain boundaries during the aging process. Continuous precipitations can either partially or completely inhibit the growth of discontinuous precipitation colonies. Obvious inhibition action on the migration of reaction front of discontinuous precipitation colonies are found by experimental results, owing to the continuous precipitates when their diameters reach up to about 5 nm or larger. The grain boundary chemical diffusion triple product sδDb is calculated according to an Aaronson-Liu model. In addition, the activation energy for discontinuous precipitation is determined to be in range between 106.7 to 113.5 kJ/mol based on Arrhenius equation, well below the activation energy for volume-bulk diffusion of Ni and Mn in Cu-rich alloy, indicating that discontinuous precipitation is easy to occur in grain boundaries.
The discontinuous and continuous precipitation behavior, and the interaction between them during the aging process in a Cu-20Ni-20Mn alloy have been investigated in the temperature range 573 K-698 K by scanning electron microscope (SEM), transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The results show that discontinuous precipitation is the predominant mechanism at 623 K and below, whereas both discontinuous and continuous precipitations occur when the temperature is higher than 673 K. The discontinuous precipitations with a lamellar mixed structure, consisting of alternate lamellae of matrix and NiMn phase, nucleate and grow preferentially on grain boundaries during the aging process. Continuous precipitations can either partially or completely inhibit the growth of discontinuous precipitation colonies. Obvious inhibition action on the migration of reaction front of discontinuous precipitation colonies are found by experimental results, owing to the continuous precipitates when their diameters reach up to about 5 nm or larger. The grain boundary chemical diffusion triple product sδDb is calculated according to an Aaronson-Liu model. In addition, the activation energy for discontinuous precipitation is determined to be in range between 106.7 to 113.5 kJ/mol based on Arrhenius equation, well below the activation energy for volume-bulk diffusion of Ni and Mn in Cu-rich alloy, indicating that discontinuous precipitation is easy to occur in grain boundaries.
2017, 46(12):3805-3810.
Abstract:
The TiB-TiC Reinforced Titanium matrix composites (TMCs) were manufactured by Laser Deposition Manufacturing (LDM) technique with the ball milled TA15+B4C powders with different compositions of B and C elements. The microstructure and wear-resistant properties of the prepared TMCs were studied by XRD, SEM, EDS, hardness test and wear resistance test. The obtained results revealed that in the prepared TMCs, there were two types of the reinforcement, namely the TiC reinforcement with the near-equiaxed shape and the TiB reinforcement with the whisker or prismatic shape. With the increase in the reinforcement content, the hardness of TMCs improved, the friction coefficient might be unchangable and the wear mass loss increased first and then decreased. Compared with the substrate, the TMC containing 1.2 wt% boron and 0.84 wt % carbon showed better wear-resistant properties. The wear mechanism of the prepared TMCs involved the abrasive wear and a small amount of oxidation wear.
The TiB-TiC Reinforced Titanium matrix composites (TMCs) were manufactured by Laser Deposition Manufacturing (LDM) technique with the ball milled TA15+B4C powders with different compositions of B and C elements. The microstructure and wear-resistant properties of the prepared TMCs were studied by XRD, SEM, EDS, hardness test and wear resistance test. The obtained results revealed that in the prepared TMCs, there were two types of the reinforcement, namely the TiC reinforcement with the near-equiaxed shape and the TiB reinforcement with the whisker or prismatic shape. With the increase in the reinforcement content, the hardness of TMCs improved, the friction coefficient might be unchangable and the wear mass loss increased first and then decreased. Compared with the substrate, the TMC containing 1.2 wt% boron and 0.84 wt % carbon showed better wear-resistant properties. The wear mechanism of the prepared TMCs involved the abrasive wear and a small amount of oxidation wear.
2017, 46(12):3811-3817.
Abstract:
In order to improve the understanding of the effectSmechanism of rare earth yttrium (Y) element on the plastic deformation of as-cast ZK30 magnesium alloy, and to use it more effectively, carried out a series of isothermal compressive tests of specimens were performed in the deformation temperature range of 573~723 K, and the strain rate range of 0.001~1 s-1 on thermo-mechanical simulator. Combing with the microstructure observation, the effects of Y (1.5wt %) on the microstructure, flow behavior, constitutive parameters and high temperature plastic properties of the ZK30 magnesium alloy were investigated. According to the hyperbolic function, constitutive parameters of the alloy were obtained by linear fitting, a nonlinear flow model and its constitutive equation have been established and employed for studying the plastic deformation behavior and the relationship between temperature, strain rate and flow stress. The results showed that Y could refine the as-cast grain and increase the amount of eutectic intermetallic compound in grain boundaries. The Y doping could effectively enhance the flow stress level and peak stress, but the change trend of true stress-strain curves are less affected. The average activation energy (Q=181.082KJ.mol-1) and stressSexponent (n=5.778) for the plastic deformation have been determinded, enlarged by 14.2% and 21.6%, respectively. The resultsSshow that theSplastic deformationSresistanceSof theSalloySis enhanced. Combined with metallurgy microstructure of these samples after deformation, Y could refine the grain and increase the amount of the dynamic recrystallization in triangle boundaries. The results showed that Y was facilitatingSdynamicSrecrystallization occur, and it was influencing theSmechanism of interface migration.
In order to improve the understanding of the effectSmechanism of rare earth yttrium (Y) element on the plastic deformation of as-cast ZK30 magnesium alloy, and to use it more effectively, carried out a series of isothermal compressive tests of specimens were performed in the deformation temperature range of 573~723 K, and the strain rate range of 0.001~1 s-1 on thermo-mechanical simulator. Combing with the microstructure observation, the effects of Y (1.5wt %) on the microstructure, flow behavior, constitutive parameters and high temperature plastic properties of the ZK30 magnesium alloy were investigated. According to the hyperbolic function, constitutive parameters of the alloy were obtained by linear fitting, a nonlinear flow model and its constitutive equation have been established and employed for studying the plastic deformation behavior and the relationship between temperature, strain rate and flow stress. The results showed that Y could refine the as-cast grain and increase the amount of eutectic intermetallic compound in grain boundaries. The Y doping could effectively enhance the flow stress level and peak stress, but the change trend of true stress-strain curves are less affected. The average activation energy (Q=181.082KJ.mol-1) and stressSexponent (n=5.778) for the plastic deformation have been determinded, enlarged by 14.2% and 21.6%, respectively. The resultsSshow that theSplastic deformationSresistanceSof theSalloySis enhanced. Combined with metallurgy microstructure of these samples after deformation, Y could refine the grain and increase the amount of the dynamic recrystallization in triangle boundaries. The results showed that Y was facilitatingSdynamicSrecrystallization occur, and it was influencing theSmechanism of interface migration.
2017, 46(12):3818-3824.
Abstract:
A micromechanical was established based on the microstructure and the fracture mechanism of TiC-TiB2 ceramic prepared by combustion synthesis under high gravity. Two different failure modes were assumed in the micromechanical model to analysis the influence of alumina inclusions to ceramic strength. The equivalent stiffness of TiC-TiB2 matrix was calculated using the Interaction Direct Derivative (IDD) estimate. The alumina particles were considered sparse distribution in the TiC-TiB2 equivalent matrix, stress field contained residual stress in and around alumina particle was obtained by the equivalent inclusion method. According to the stress field around the particles, Al2O3 particles failure was considered as the origin of the composite fracture. Interface debonding and particle fracture were assumed as the two failure modes of particle failure, micro strength mechanical models based on these two modes were established and the minimum strength was defined as the composite strength. Composite strength variation with microstructure parameters and property parameters of different micro components was obtained, and the calculated strength was compared to the experimental data. The result shows that the strength model is reasonable in reflecting the composites failure mechanism; relative elastic and thermal properties between the particle and matrix, particle size and the equivalent matrix toughness can change the particle failure mode, and the particle size increasing and the equivalent matrix toughness decreasing result in composite strength necessarily. For TiC-TiB2 combustion synthesis composite with alumina inclusions, particle interface debonding is the primary fracture mechanism.
A micromechanical was established based on the microstructure and the fracture mechanism of TiC-TiB2 ceramic prepared by combustion synthesis under high gravity. Two different failure modes were assumed in the micromechanical model to analysis the influence of alumina inclusions to ceramic strength. The equivalent stiffness of TiC-TiB2 matrix was calculated using the Interaction Direct Derivative (IDD) estimate. The alumina particles were considered sparse distribution in the TiC-TiB2 equivalent matrix, stress field contained residual stress in and around alumina particle was obtained by the equivalent inclusion method. According to the stress field around the particles, Al2O3 particles failure was considered as the origin of the composite fracture. Interface debonding and particle fracture were assumed as the two failure modes of particle failure, micro strength mechanical models based on these two modes were established and the minimum strength was defined as the composite strength. Composite strength variation with microstructure parameters and property parameters of different micro components was obtained, and the calculated strength was compared to the experimental data. The result shows that the strength model is reasonable in reflecting the composites failure mechanism; relative elastic and thermal properties between the particle and matrix, particle size and the equivalent matrix toughness can change the particle failure mode, and the particle size increasing and the equivalent matrix toughness decreasing result in composite strength necessarily. For TiC-TiB2 combustion synthesis composite with alumina inclusions, particle interface debonding is the primary fracture mechanism.
2017, 46(12):3825-3831.
Abstract:
Using WB powder and WC-Co powder as raw materials, the cemented carbides with different volume fraction of WB additives were prepared by hot isostatic pressing (HIP) method. Then, the phase constitution, microstructure and mechanical properties of the prepared cemented carbides have been studied. The results show that the super hard WCoB phase is formed by the reaction of WB and Co. With the decrease of Co phase, less WC grains were seperated.. With the increase of the WB addition, the prepared cemented carbides have a lower frictionScoefficients and a better wear resistance and hardness. When the WB addition is 30wt%, the hardness of 1900kg/mm2 can beattained. The abrasion loss of the sample is 1/10 of that of the WC-Co cemented carbide. However, the fracture toughness of the cemented carbide with WB addition is about 83%-91% of that of the conventional WC-Co cemented carbides.
Using WB powder and WC-Co powder as raw materials, the cemented carbides with different volume fraction of WB additives were prepared by hot isostatic pressing (HIP) method. Then, the phase constitution, microstructure and mechanical properties of the prepared cemented carbides have been studied. The results show that the super hard WCoB phase is formed by the reaction of WB and Co. With the decrease of Co phase, less WC grains were seperated.. With the increase of the WB addition, the prepared cemented carbides have a lower frictionScoefficients and a better wear resistance and hardness. When the WB addition is 30wt%, the hardness of 1900kg/mm2 can beattained. The abrasion loss of the sample is 1/10 of that of the WC-Co cemented carbide. However, the fracture toughness of the cemented carbide with WB addition is about 83%-91% of that of the conventional WC-Co cemented carbides.
2017, 46(12):3832-3837.
Abstract:
In this research, the effect of phytic acid on bioactivity of the surface of SLA-titanium was studied, through modification with phytic acid and subsequent mineralization in the simulated body fluid (SBF). The microstructure, chemical properties and wettability was demonstrated, using SEM、EDS and contact angle analysis. Human bone marrow stromal cells (hBMSCs) were cultured on different surfaces to investigate the proliferation, adhesion and differentiation. The results demonstrate that the contact angle of surface modified with phytic acid is 0°, which means it is superhydrophilicity. The ability to induce apatite deposition, as well as the proliferation, adhesion differentiation of cells are improved obviously on SLA-surface, which reflect a better bioactivation treatment as a result of using phytic acid solution.
In this research, the effect of phytic acid on bioactivity of the surface of SLA-titanium was studied, through modification with phytic acid and subsequent mineralization in the simulated body fluid (SBF). The microstructure, chemical properties and wettability was demonstrated, using SEM、EDS and contact angle analysis. Human bone marrow stromal cells (hBMSCs) were cultured on different surfaces to investigate the proliferation, adhesion and differentiation. The results demonstrate that the contact angle of surface modified with phytic acid is 0°, which means it is superhydrophilicity. The ability to induce apatite deposition, as well as the proliferation, adhesion differentiation of cells are improved obviously on SLA-surface, which reflect a better bioactivation treatment as a result of using phytic acid solution.
2017, 46(12):3838-3842.
Abstract:
Coatings for preventing hydrogen escaping were formed on disk-type ZrH1.8 by in-situ oxidation method. Urea was placed and in vacuum chamber and decomposed into complicated chemical compound including carbon, nitrogen, oxygen source. The phase structure and morphology of coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The composition and depth of elements, bond states were tested by auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) technique. The results indicate that weight of coatings increased with temperatures rised. XRD shows the phase structure of coatings consists mainly of ZrN and ZrO2, including monoclinic ZrO2 (m-ZrO2) and tetragonal ZrO2 (t-ZrO2). SEM depicts coatings were accumulated and combined densely with substrate. AES indicates that the coating is mainly composed of carbon, nitrogen, oxygen and zirconium, which show that the atomic concentration of carbon and nitrogen decreased continuously, while, oxygen and zirconium increased with sputter time incresing. XPS shows that coating was including Zr-O、Zr-C、Zr-N-O、Zr-N、O-H bonds. It is possible the C, N, O atoms synergistic effect, making the coating has good resistance hydrogen permeation.
Coatings for preventing hydrogen escaping were formed on disk-type ZrH1.8 by in-situ oxidation method. Urea was placed and in vacuum chamber and decomposed into complicated chemical compound including carbon, nitrogen, oxygen source. The phase structure and morphology of coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The composition and depth of elements, bond states were tested by auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) technique. The results indicate that weight of coatings increased with temperatures rised. XRD shows the phase structure of coatings consists mainly of ZrN and ZrO2, including monoclinic ZrO2 (m-ZrO2) and tetragonal ZrO2 (t-ZrO2). SEM depicts coatings were accumulated and combined densely with substrate. AES indicates that the coating is mainly composed of carbon, nitrogen, oxygen and zirconium, which show that the atomic concentration of carbon and nitrogen decreased continuously, while, oxygen and zirconium increased with sputter time incresing. XPS shows that coating was including Zr-O、Zr-C、Zr-N-O、Zr-N、O-H bonds. It is possible the C, N, O atoms synergistic effect, making the coating has good resistance hydrogen permeation.
42 Effect of TiAl3 Phase on Dry Wear Behaviorof In-situ TiC/Al-4.5Cu Composites at Elevated Temperature
2017, 46(12):3843-3848.
Abstract:
In-situ TiC/Al-4.5Cu composites were made by direct reaction synthesis (DRS) and the effect of TiAl3 phase on the dry wear behavior of the in-situ TiC/Al-4.5Cu composites from 100℃ to 250℃ was studied. The results show that the wear loss of in-situ TiC/Al-4.5Cu increases with the load increasing from 15 to 55N at elevated temperature. The wear loss of the composites containing TiAl3 phase is always larger. There is a critical transition temperature (CTT) of severe wear when the load excesses 35N and the composites with TiAl3 phase possess lower CTT. TiAl3 phase degrades the wear resistance of in-situ TiC/Al-4.5Cu composites.
In-situ TiC/Al-4.5Cu composites were made by direct reaction synthesis (DRS) and the effect of TiAl3 phase on the dry wear behavior of the in-situ TiC/Al-4.5Cu composites from 100℃ to 250℃ was studied. The results show that the wear loss of in-situ TiC/Al-4.5Cu increases with the load increasing from 15 to 55N at elevated temperature. The wear loss of the composites containing TiAl3 phase is always larger. There is a critical transition temperature (CTT) of severe wear when the load excesses 35N and the composites with TiAl3 phase possess lower CTT. TiAl3 phase degrades the wear resistance of in-situ TiC/Al-4.5Cu composites.
2017, 46(12):3849-3852.
Abstract:
Diffusion bonding of pure aluminum to pure nickel by organic solvent surface protection has been investigated at various temperatures. The interfacial microstructure of Al/Ni diffusion bonded joint was confirmed to be Al/Al3Ni2/Ni by scanning electron microscope, energy spectrum analysis and X-ray diffraction (XRD) analysis method. The organic solvent was used to protect the "clean surface" against re-oxidation prior to diffusion bonding. Under optimum conditions, the joints with higher shear strength were obtained. As the temperature increased, the thickness of the reaction layers increased gradually. The highest shear strength obtained by organic solvent surface protection bonding was17.83MPa under a pressure of 2MPa for 60 min at temperatures of 490°C, which was 55% higher than those obtained by conventional diffusion bonding.
Diffusion bonding of pure aluminum to pure nickel by organic solvent surface protection has been investigated at various temperatures. The interfacial microstructure of Al/Ni diffusion bonded joint was confirmed to be Al/Al3Ni2/Ni by scanning electron microscope, energy spectrum analysis and X-ray diffraction (XRD) analysis method. The organic solvent was used to protect the "clean surface" against re-oxidation prior to diffusion bonding. Under optimum conditions, the joints with higher shear strength were obtained. As the temperature increased, the thickness of the reaction layers increased gradually. The highest shear strength obtained by organic solvent surface protection bonding was17.83MPa under a pressure of 2MPa for 60 min at temperatures of 490°C, which was 55% higher than those obtained by conventional diffusion bonding.
2017, 46(12):3853-3857.
Abstract:
:TiO2 nanopore array was firstly prepared by three-stepped anodization process, and subsequently Ag nanoparticles with sizes of 30 nm were deposited on TiO2 nanoarray through a continuous ion layer adsorption. The resulting Ag/TiO2 nanopore array was then used as a surface enhanced Raman scattering (SERS) active substrate, and their uniformity, stability and recyclability were investigated. The results showed that the Ag/TiO2 substrates delivered a detection limit of up to ~10-7 mol/L under excitation at 532 nm. Moreover, the substrates exhibited outstanding uniformity and stability. The Ag/TiO2 nanoarray also conducted photocatalysis decomposition of adsorbed R6G molecules after 30 min irradiation under simulated solar light, exhibiting high recyclability. Such a Ag/TiO2 nanopore array has great potential as an ideal SERS active substrate due to its highly ordered structure and excellent properties.
:TiO2 nanopore array was firstly prepared by three-stepped anodization process, and subsequently Ag nanoparticles with sizes of 30 nm were deposited on TiO2 nanoarray through a continuous ion layer adsorption. The resulting Ag/TiO2 nanopore array was then used as a surface enhanced Raman scattering (SERS) active substrate, and their uniformity, stability and recyclability were investigated. The results showed that the Ag/TiO2 substrates delivered a detection limit of up to ~10-7 mol/L under excitation at 532 nm. Moreover, the substrates exhibited outstanding uniformity and stability. The Ag/TiO2 nanoarray also conducted photocatalysis decomposition of adsorbed R6G molecules after 30 min irradiation under simulated solar light, exhibiting high recyclability. Such a Ag/TiO2 nanopore array has great potential as an ideal SERS active substrate due to its highly ordered structure and excellent properties.
2017, 46(12):3858-3861.
Abstract:
Cold spray was used to prepare the AgSnO2 coating on copper substrates with high energy ball milled Ag-SnO2 composite powders. The increased density, migration of Ag-rich phase toward the boundaries of original composite powders and decreased hardness occurred for the cold sprayed coatings during annealing at 850 ℃. It was found by the arcing and electrical contact experiments that there is low and stable contact resistance for the AgSnO2 coating, which can be used in the low voltage apparatus.
Cold spray was used to prepare the AgSnO2 coating on copper substrates with high energy ball milled Ag-SnO2 composite powders. The increased density, migration of Ag-rich phase toward the boundaries of original composite powders and decreased hardness occurred for the cold sprayed coatings during annealing at 850 ℃. It was found by the arcing and electrical contact experiments that there is low and stable contact resistance for the AgSnO2 coating, which can be used in the low voltage apparatus.
2017, 46(12):3862-3867.
Abstract:
Novel graphene reinforced CuCr25 matrix composites (GCMC) with high hardness and conductivity are successfully prepared by spark plasma sintering (SPS) under high pressure and low temperature after low speed ball-milling mix. It is confirmed that the graphene is remained and no new phase is found by X-ray diffraction and Raman spectroscopy. Structural characterization of GCMC is performed using field emission scanning electron microscope（SEM） and energy dispersive spectroscopy（EDS）, which reveals that the graphene is homogeneously distributed in matrix after sintering process. The hardness of GCMC with 1wt.% graphene sintered under 300MPa and 600°C is increased by 11.3% than the values of CuCr25 alloys fabricated by the same method, though the conductivity is decreased by 4.2%. Comparing with the CuCr25 alloys consolidated by conventional method, the conductivity and hardness of new-type GCMC are about 1.35 and 1.48 times higher respectively, which indicates that the additional phase and new process all make contributions to the enhancement of GCMC.
Novel graphene reinforced CuCr25 matrix composites (GCMC) with high hardness and conductivity are successfully prepared by spark plasma sintering (SPS) under high pressure and low temperature after low speed ball-milling mix. It is confirmed that the graphene is remained and no new phase is found by X-ray diffraction and Raman spectroscopy. Structural characterization of GCMC is performed using field emission scanning electron microscope（SEM） and energy dispersive spectroscopy（EDS）, which reveals that the graphene is homogeneously distributed in matrix after sintering process. The hardness of GCMC with 1wt.% graphene sintered under 300MPa and 600°C is increased by 11.3% than the values of CuCr25 alloys fabricated by the same method, though the conductivity is decreased by 4.2%. Comparing with the CuCr25 alloys consolidated by conventional method, the conductivity and hardness of new-type GCMC are about 1.35 and 1.48 times higher respectively, which indicates that the additional phase and new process all make contributions to the enhancement of GCMC.
2017, 46(12):3868-3874.
Abstract:
An artificial-neural-network (ANN) model which is used for the prediction of properties of the as-milled powder is developed for the analysis and prediction of correlations between processing (high-energy planetary ball milling) parameters and the morphological characteristics of Ti2AlNb-based alloy powder by applying the back-propagation (BP) neural network technique.In the BP model, the input parameters of the neural network model are milling speed, milling time and ball-to-powder weight ratio. The output of the model is the properties of the as-milled powder (specifically crystallite size). The number of node in the hidden layer is 9. Input and output functions are tansig and purelin, respectively. The accuracy of the established artificial neural network model was tested by the test data sample. It is shown that the predicted values coincide well with the test results owe to the advantages in fault-tolerance and commonality. Not only can the trained neural network model be used to predict the crystallite size of the as-milled Ti2AlNb-based alloy powder, but also can make up for deficiency of all kinds of physical model for ball milling process in application and expression, which has application value and far-reaching significance for the research work of the actual powder metallurgy process.
An artificial-neural-network (ANN) model which is used for the prediction of properties of the as-milled powder is developed for the analysis and prediction of correlations between processing (high-energy planetary ball milling) parameters and the morphological characteristics of Ti2AlNb-based alloy powder by applying the back-propagation (BP) neural network technique.In the BP model, the input parameters of the neural network model are milling speed, milling time and ball-to-powder weight ratio. The output of the model is the properties of the as-milled powder (specifically crystallite size). The number of node in the hidden layer is 9. Input and output functions are tansig and purelin, respectively. The accuracy of the established artificial neural network model was tested by the test data sample. It is shown that the predicted values coincide well with the test results owe to the advantages in fault-tolerance and commonality. Not only can the trained neural network model be used to predict the crystallite size of the as-milled Ti2AlNb-based alloy powder, but also can make up for deficiency of all kinds of physical model for ball milling process in application and expression, which has application value and far-reaching significance for the research work of the actual powder metallurgy process.
2017, 46(12):3875-3881.
Abstract:
The radial forging strain-induced melt activation (RFSIMA) is adopted to process the as-extruded 6063 aluminum alloy. In this research, the influence of radial forging on the microstructure of as-extruded 6063 aluminum alloy has been investigated. The semi-solid microstructural evolution generated by the directly semi-solid isothermal treatment, and initially radial forging predeformation and then semi-solid isothermal treatment have been analyzed. The results indicated that the compaction degree of RF-deformed 6063 aluminum alloy microstructure gradually increases as the area reduction increases. However, this increasing pattern is not obviously when the area reduction increases from 70% to 85%. In addition, the more ideal semi-solid microstructure can be obtained through RFSIMA as compared with the directly semi-solid isothermal treatment.
The radial forging strain-induced melt activation (RFSIMA) is adopted to process the as-extruded 6063 aluminum alloy. In this research, the influence of radial forging on the microstructure of as-extruded 6063 aluminum alloy has been investigated. The semi-solid microstructural evolution generated by the directly semi-solid isothermal treatment, and initially radial forging predeformation and then semi-solid isothermal treatment have been analyzed. The results indicated that the compaction degree of RF-deformed 6063 aluminum alloy microstructure gradually increases as the area reduction increases. However, this increasing pattern is not obviously when the area reduction increases from 70% to 85%. In addition, the more ideal semi-solid microstructure can be obtained through RFSIMA as compared with the directly semi-solid isothermal treatment.
2017, 46(12):3882-3886.
Abstract:
Graphene reinforced titanium composites were prepared by spark plasma sintering at 850℃ following a powder metallurgy process. The compressive properties of the composites at room temperature and 850℃were examined using a Gleeble-1500D. It is found that graphene is well dispersed in titanium matrix, refining the matrix microstructure and improving the compressive strength and hardness of the matrix at the room and high temperatures. In particular, the yield strength at room and temeperature increases by 22.87% and 23.07% respectively; compressive strength increases by 13.91% and 28.57% respectively; hardness increases by 16.4% and 10% respectively. Meanwhile, the result indicates small portion of graphene react with titanium matrix and leads to the formation of titanium carbides and reinforce the matrix. The results presented in this work denmonstrates the graphene/titanium composite is a type of high performance material and can have potential engineering applications.
Graphene reinforced titanium composites were prepared by spark plasma sintering at 850℃ following a powder metallurgy process. The compressive properties of the composites at room temperature and 850℃were examined using a Gleeble-1500D. It is found that graphene is well dispersed in titanium matrix, refining the matrix microstructure and improving the compressive strength and hardness of the matrix at the room and high temperatures. In particular, the yield strength at room and temeperature increases by 22.87% and 23.07% respectively; compressive strength increases by 13.91% and 28.57% respectively; hardness increases by 16.4% and 10% respectively. Meanwhile, the result indicates small portion of graphene react with titanium matrix and leads to the formation of titanium carbides and reinforce the matrix. The results presented in this work denmonstrates the graphene/titanium composite is a type of high performance material and can have potential engineering applications.
2017, 46(12):3887-3892.
Abstract:
Using tungsten oxide, cobalt oxide and carbon black as the raw materials. The nano WC-Co composite powders with pure phases was synthesized by in-situ reduction and carburization reactions. The particle size of prepared WC-Co composite powders is about 80 nm. In this work, the effects of preparation conditions on the phase formation, particle size and oxygen content of the composite powders and on the microstructure and mechanical property of the sintered bulk were investigated. The results indicate that the decarburization reaction will happen in the process of sintering when the oxygen content of the composite powders is higher, leading to a decrease in density and mechanical property of the sintered bulk. The oxygen content declines significantly, with heat treated for two and a half hours, under the heat treatment temperature of 800 oC. Meanwhile, the mean particle size with heat-treated is 85 nm, without markedly increase. Using heat-treated composite powders with the addition of 1.1%TiC and 0.9%VC grain growth inhibitors, the nano-grained WC-Co bulk by SPS was obtained, with an average grain size of 105nm. The hardness values and fracture toughness obtained are 2145Hv30 and 9.81MPam1/2 , superior to unheated sample.
Using tungsten oxide, cobalt oxide and carbon black as the raw materials. The nano WC-Co composite powders with pure phases was synthesized by in-situ reduction and carburization reactions. The particle size of prepared WC-Co composite powders is about 80 nm. In this work, the effects of preparation conditions on the phase formation, particle size and oxygen content of the composite powders and on the microstructure and mechanical property of the sintered bulk were investigated. The results indicate that the decarburization reaction will happen in the process of sintering when the oxygen content of the composite powders is higher, leading to a decrease in density and mechanical property of the sintered bulk. The oxygen content declines significantly, with heat treated for two and a half hours, under the heat treatment temperature of 800 oC. Meanwhile, the mean particle size with heat-treated is 85 nm, without markedly increase. Using heat-treated composite powders with the addition of 1.1%TiC and 0.9%VC grain growth inhibitors, the nano-grained WC-Co bulk by SPS was obtained, with an average grain size of 105nm. The hardness values and fracture toughness obtained are 2145Hv30 and 9.81MPam1/2 , superior to unheated sample.
2017, 46(12):3893-3896.
Abstract:
W-Ni-Cu compound materials were?obtained?by?using?fused-salt?electrolysis?method?and?aqueous?solution?electrolysis?method. W-Ni-Cu?functional?graded?materials?(FGM)?characterized?with?different?thickness?(25 μm,?35 μm?and?45 μm) were obtained from its compound materials after annealing at?800 ℃ for?60min,?120min?and?180min, respectively, Ni plays a role in bridging Cu and W. Cracks and abscission were not presented?in?the?surface?of?samples?after?thermal?shock?and?thermal?fatigue,?which?indicates?the?material?has?good?bonding?properties. Thermal ?conductivity?tests?were?also?conducted,?the?result?shows?that?the?thermal?conductivity?of?pure?W?plate?and?W-Ni-Cu FGM decrease with increasing temperature (25～800 ℃). The thermal conductivity of pure W plate is higher than that of W-Ni-Cu FGM at the same temperature. The thermal conductivity of W-Ni-Cu FGM decreases with increasing gradient thickness.
W-Ni-Cu compound materials were?obtained?by?using?fused-salt?electrolysis?method?and?aqueous?solution?electrolysis?method. W-Ni-Cu?functional?graded?materials?(FGM)?characterized?with?different?thickness?(25 μm,?35 μm?and?45 μm) were obtained from its compound materials after annealing at?800 ℃ for?60min,?120min?and?180min, respectively, Ni plays a role in bridging Cu and W. Cracks and abscission were not presented?in?the?surface?of?samples?after?thermal?shock?and?thermal?fatigue,?which?indicates?the?material?has?good?bonding?properties. Thermal ?conductivity?tests?were?also?conducted,?the?result?shows?that?the?thermal?conductivity?of?pure?W?plate?and?W-Ni-Cu FGM decrease with increasing temperature (25～800 ℃). The thermal conductivity of pure W plate is higher than that of W-Ni-Cu FGM at the same temperature. The thermal conductivity of W-Ni-Cu FGM decreases with increasing gradient thickness.
2017, 46(12):3897-3902.
Abstract:
The addition of proper amount of calcium to magnesium alloys can refine grain size, enhance strength and heat-resistant. The influence of different contents of calcium (Ca) on the grain size, texture and mechanical properties of Mg-2Al-xCa-0.2Gd (x=0.2, 0.5, 1.0, 2.0; mass%) were investigated in this paper through the OM, SEM，EBSD and XRD techniques. The results showed that with the increase of the Ca content the grain size gradually decreased which leads to the improvement of strength. However, the texture evolution had different characterization such as the decrease of {0001}<11 0> texture, the firstly increase and then decrease of the pyramidal texture components containing the <11 3> direction, which resulted in the corresponding change of elongation and Erichsen value. The magnesium alloy with 0.5% calcium content exhibited bimodal texture characterization and showed the best mechanical properties with the maximal tensile strength of 238MPa, the total elongation of 22% and the Erichsen value of 4.31mm.
The addition of proper amount of calcium to magnesium alloys can refine grain size, enhance strength and heat-resistant. The influence of different contents of calcium (Ca) on the grain size, texture and mechanical properties of Mg-2Al-xCa-0.2Gd (x=0.2, 0.5, 1.0, 2.0; mass%) were investigated in this paper through the OM, SEM，EBSD and XRD techniques. The results showed that with the increase of the Ca content the grain size gradually decreased which leads to the improvement of strength. However, the texture evolution had different characterization such as the decrease of {0001}<11 0> texture, the firstly increase and then decrease of the pyramidal texture components containing the <11 3> direction, which resulted in the corresponding change of elongation and Erichsen value. The magnesium alloy with 0.5% calcium content exhibited bimodal texture characterization and showed the best mechanical properties with the maximal tensile strength of 238MPa, the total elongation of 22% and the Erichsen value of 4.31mm.
2017, 46(12):3903-3909.
Abstract:
Ultrafine WC powder was chosed and ultrafine crystalline gradient cemented carbides was prepared by a two-step sintering process, where the cemented carbides is first lower pressure pre-sintered and then subjected to a gradient sintering. The influences of cubic phase on microstructure and property of ultrafine crystalline gradient cemented carbides have been studied. The results show that the thicker gradient layer can be form in alloy with only adding Ti(C,N), but the mean WC grains size has a large value after gradient sintering. The thinner gradient layer has been formed when (W,Ti)C or (Nb,Ta)C was added, but the mean WC grains size is smaller than the alloy with only adding Ti(C,N). Some WC grains with size above 1 μm has been formed in the alloy with adding (W,Ti)C after gradient sintering. The formation of the core-rim structure cubic phase can be prevent by adding (Ta,Nb)C.
Ultrafine WC powder was chosed and ultrafine crystalline gradient cemented carbides was prepared by a two-step sintering process, where the cemented carbides is first lower pressure pre-sintered and then subjected to a gradient sintering. The influences of cubic phase on microstructure and property of ultrafine crystalline gradient cemented carbides have been studied. The results show that the thicker gradient layer can be form in alloy with only adding Ti(C,N), but the mean WC grains size has a large value after gradient sintering. The thinner gradient layer has been formed when (W,Ti)C or (Nb,Ta)C was added, but the mean WC grains size is smaller than the alloy with only adding Ti(C,N). Some WC grains with size above 1 μm has been formed in the alloy with adding (W,Ti)C after gradient sintering. The formation of the core-rim structure cubic phase can be prevent by adding (Ta,Nb)C.
2017, 46(12):3910-3915.
Abstract:
The effect of Cu content on the corrosion resistance of Zr-1Nb-xCu alloys (x=0~0.5, mass fraction, %) was investigated in superheated steam at 400 ℃ and 10.3 MPa by autoclave tests. The microstructure of the alloys and the fracture surface of oxide films on the corroded specimens were observed by TEM and SEM, respectively. The results show that when the addition of Cu in the Zr-1Nb alloys is below 0.2%, the main second phase particles (SPPs) are β-Nb in smaller size, and Cu mainly dissolved in the α-Zr matrix, the corrosion resistance of the alloys is improved markedly with the increase of Cu content. When the addition of Cu is above 0.2%, the SPPs of Zr2Cu are precipitated. The size and amount of Zr2Cu particles become larger with the increase of Cu content. The Zr-1Nb-0.35Cu alloy, in which the SPPs of Zr2Cu are moderate in size and amount, shows the best corrosion resistance. However, the Zr-1Nb-0.5Cu alloy, in which the SPPs of Zr2Cu are larger and more, shows the worst corrosion resistance and nodular corrosion appeares during the autoclave tests in superheated steam at 400 ℃.
The effect of Cu content on the corrosion resistance of Zr-1Nb-xCu alloys (x=0~0.5, mass fraction, %) was investigated in superheated steam at 400 ℃ and 10.3 MPa by autoclave tests. The microstructure of the alloys and the fracture surface of oxide films on the corroded specimens were observed by TEM and SEM, respectively. The results show that when the addition of Cu in the Zr-1Nb alloys is below 0.2%, the main second phase particles (SPPs) are β-Nb in smaller size, and Cu mainly dissolved in the α-Zr matrix, the corrosion resistance of the alloys is improved markedly with the increase of Cu content. When the addition of Cu is above 0.2%, the SPPs of Zr2Cu are precipitated. The size and amount of Zr2Cu particles become larger with the increase of Cu content. The Zr-1Nb-0.35Cu alloy, in which the SPPs of Zr2Cu are moderate in size and amount, shows the best corrosion resistance. However, the Zr-1Nb-0.5Cu alloy, in which the SPPs of Zr2Cu are larger and more, shows the worst corrosion resistance and nodular corrosion appeares during the autoclave tests in superheated steam at 400 ℃.
2017, 46(12):3916-3921.
Abstract:
cBN-WC-12Co cemented carbides were prepared by spark plasma sintering (SPS) technique in this paper. The thermal stability of cBN was analyzed. The effect of cBN content and sintering temperature on the hardness and density of the cemented carbides were discussed, and the strengthening mechanism of cBN was discussed. The results show that the thermal stability temperature of cBN is 1335℃. The lowest dense sintering temperature of cBN-WC-12Co cemented carbides is about 1150℃, and cBN keeps an ideal thermal stability with no phase transition at 1250℃. The density of cBN-WC-12Co cemented carbides is better than WC-12Co at the same sintering temperature; The alloy C15 sintered at 1150℃ is with the highest density and hardness (HV10), which are 99.7% and1997,respectively; The increase of cBN content is beneficial to inhibit the growth of WC grains, to a certain degree, when the content of cBN is lower than 15vol%. The smaller WC grain is helpful to promote the densification of the cemented carbides through its capillary adsorption ,while the cBN can prevent the spread of crack and other defects, then to improve the mechanical properties of the cemented carbides.
cBN-WC-12Co cemented carbides were prepared by spark plasma sintering (SPS) technique in this paper. The thermal stability of cBN was analyzed. The effect of cBN content and sintering temperature on the hardness and density of the cemented carbides were discussed, and the strengthening mechanism of cBN was discussed. The results show that the thermal stability temperature of cBN is 1335℃. The lowest dense sintering temperature of cBN-WC-12Co cemented carbides is about 1150℃, and cBN keeps an ideal thermal stability with no phase transition at 1250℃. The density of cBN-WC-12Co cemented carbides is better than WC-12Co at the same sintering temperature; The alloy C15 sintered at 1150℃ is with the highest density and hardness (HV10), which are 99.7% and1997,respectively; The increase of cBN content is beneficial to inhibit the growth of WC grains, to a certain degree, when the content of cBN is lower than 15vol%. The smaller WC grain is helpful to promote the densification of the cemented carbides through its capillary adsorption ,while the cBN can prevent the spread of crack and other defects, then to improve the mechanical properties of the cemented carbides.
2017, 46(12):3922-3927.
Abstract:
Zirconium alloy fuel cladding picks up hydrogen during operation through a corrosion reaction with coolant water, which reduces the ductility of the cladding. However, there is a connection between the extent of hydride embrittlement and hydrogen concentration. The effect of hydrides formed by the gas hydrogen charging method with hydrogen content between 100~1000 μg/g on the ring tensile properties of N36 zirconium alloy cladding tubes of was investigated. It was found that the ductility reduced with the increasing of hydrogen concentration when exceeding 150 μg/g hydrogen content level, the ductility reduced to 9% when the hydrogen content was about 1000 μg/g, still remain a certain ductility. But the hydrogen concentration had little effect on the tensile strength and yield strength. The fracture pattern was found to depend strongly on the hydrogen concentration . With the increase of hydrogen , the fracture types were45°shear type fracture, cup and cone type fracture and chisel edge type fracture.
Zirconium alloy fuel cladding picks up hydrogen during operation through a corrosion reaction with coolant water, which reduces the ductility of the cladding. However, there is a connection between the extent of hydride embrittlement and hydrogen concentration. The effect of hydrides formed by the gas hydrogen charging method with hydrogen content between 100~1000 μg/g on the ring tensile properties of N36 zirconium alloy cladding tubes of was investigated. It was found that the ductility reduced with the increasing of hydrogen concentration when exceeding 150 μg/g hydrogen content level, the ductility reduced to 9% when the hydrogen content was about 1000 μg/g, still remain a certain ductility. But the hydrogen concentration had little effect on the tensile strength and yield strength. The fracture pattern was found to depend strongly on the hydrogen concentration . With the increase of hydrogen , the fracture types were45°shear type fracture, cup and cone type fracture and chisel edge type fracture.
2017, 46(12):3928-3934.
Abstract:
TNZS, TiO2/TNZS, HA/TNZS titanium-based biomedical materials were prepared by powder Metallurgy comebining high-energy ball milling, conventional vacuum and non-pressure sintering. The tribological properties and microhardness of the three sintering bodies were investigated. The results show that under the condition of room temperature, load of 100 g, frequency of 10 HZ, dry friction and Si3N4 ceramic ball for 15 min, HA/TNZS titanium-based biomedical material has low friction coefficient and the best wear resistance; friction coefficients are 0.4323, 0.5643 and 0.4338, and the average width of wear scars are 0.33 mm, 0.26 mm and 0.18 mm, respectively ; wear mechanism of all is abrasive wear, supplemented with oxidation wear and adhesive wear; the average friction coefficients and wear of all materials under artificial body fluid are better than those under dry friction , and wear resistence of HA/TNZS is better than the other two; the average friction coefficient of all are 0.3309, 0.4301 and 0.3840, and the average width of wear scars are 0.27 mm,0.19 mm and 0.17 mm, respectively; wear mechanism are abrasive wear, accompanied by mild oxidation wear and adhesive wear；TiO2/TNZS has the highest microhardness value, and the microhardness values of the three are 525.43 HV, 551.23 HV and 479.27 HV.
TNZS, TiO2/TNZS, HA/TNZS titanium-based biomedical materials were prepared by powder Metallurgy comebining high-energy ball milling, conventional vacuum and non-pressure sintering. The tribological properties and microhardness of the three sintering bodies were investigated. The results show that under the condition of room temperature, load of 100 g, frequency of 10 HZ, dry friction and Si3N4 ceramic ball for 15 min, HA/TNZS titanium-based biomedical material has low friction coefficient and the best wear resistance; friction coefficients are 0.4323, 0.5643 and 0.4338, and the average width of wear scars are 0.33 mm, 0.26 mm and 0.18 mm, respectively ; wear mechanism of all is abrasive wear, supplemented with oxidation wear and adhesive wear; the average friction coefficients and wear of all materials under artificial body fluid are better than those under dry friction , and wear resistence of HA/TNZS is better than the other two; the average friction coefficient of all are 0.3309, 0.4301 and 0.3840, and the average width of wear scars are 0.27 mm,0.19 mm and 0.17 mm, respectively; wear mechanism are abrasive wear, accompanied by mild oxidation wear and adhesive wear；TiO2/TNZS has the highest microhardness value, and the microhardness values of the three are 525.43 HV, 551.23 HV and 479.27 HV.
2017, 46(12):3935-3940.
Abstract:
In this paper, the evolution of cavitation corrosion of Ti-6Al-4V alloy in LiBr solution was discussed by means of SEM, roughness profiler, three-dimensional video microscope and electrochemical measurement. The results of the variation of surface roughness value (Rq), mean cavitation corrosion depth and morphological features indicate that there are three stages of cavitation corrosion process of Ti-6Al-4V alloy. At initial stage, the value of Rq increases linearly with time; at transition stage, the growth rate of Rq decreases; when the steady-state stage reaches, the value of Rq tends to stabilize. Plastic deformation of the low intensive α phase of Ti-6Al-4V alloy occurs preferentially due to absorption of impact energy generated by bubble collapse, causing uneven deformation of material surface. Passive film on the surface of α phase in local area is easily attacked and fresh titanium alloy substrate is exposed. Small anode and large cathode form due to relatively low electric potential of α phase in comparison with β phase, meanwhile corrosives and corrosion products diffuse fast with the aid of agitation of cavitation, leading to the acceleration of the corrosion dissolution. The growth of pits causes the concentration of local internal stress, which strengthens the mechanical factor, accordingly increases the degree of surface concave and convex. The synergetic effect of mechanics and electrochemical corrosion results in the development of the existing pits and emergence of new pits. Eventually β phase distributed at the boundary of pits falls off and the degree of surface concave and convex becomes small. At the initial stage, electrochemical corrosion promotes mechanical effect of cavitation.
In this paper, the evolution of cavitation corrosion of Ti-6Al-4V alloy in LiBr solution was discussed by means of SEM, roughness profiler, three-dimensional video microscope and electrochemical measurement. The results of the variation of surface roughness value (Rq), mean cavitation corrosion depth and morphological features indicate that there are three stages of cavitation corrosion process of Ti-6Al-4V alloy. At initial stage, the value of Rq increases linearly with time; at transition stage, the growth rate of Rq decreases; when the steady-state stage reaches, the value of Rq tends to stabilize. Plastic deformation of the low intensive α phase of Ti-6Al-4V alloy occurs preferentially due to absorption of impact energy generated by bubble collapse, causing uneven deformation of material surface. Passive film on the surface of α phase in local area is easily attacked and fresh titanium alloy substrate is exposed. Small anode and large cathode form due to relatively low electric potential of α phase in comparison with β phase, meanwhile corrosives and corrosion products diffuse fast with the aid of agitation of cavitation, leading to the acceleration of the corrosion dissolution. The growth of pits causes the concentration of local internal stress, which strengthens the mechanical factor, accordingly increases the degree of surface concave and convex. The synergetic effect of mechanics and electrochemical corrosion results in the development of the existing pits and emergence of new pits. Eventually β phase distributed at the boundary of pits falls off and the degree of surface concave and convex becomes small. At the initial stage, electrochemical corrosion promotes mechanical effect of cavitation.
2017, 46(12):3941-3946.
Abstract:
MoFeCrTiWSix (x=0, 0.2, 0.4, 0.6, 0.8, 1.0) multi-principal element alloy coatings were fabricated on Q235 steel by laser cladding. The effect of silicon on the microstructure, phases, microhardness and high-temperature oxidation resistance were investigated systematically by X-ray diffraction (XRD), scanning electron microscopy (SEM) and microhardness tester etc. The results show that, the phase of laser cladding MoFeCrTiW multi-principal element alloy coating is single BCC structure and its microstructure is equiaxed grains. The main phase is still BCC structure after adding different content of silicon into coating. When the content of silicon is no less than 0.4 moles, there exits small intermetallic compound in the coatings, the microstructures of coatings are composed of proeutectic BCC phase and eutectic structure of BCC phase and Cr5Fe50Mo8.9Si5.2Ti20.4 phase. With the content of silicon increasing, the morphology of proeutectic phase changes from cystiform-dendritic to columnar dendrites and equiaxed dendrites, while the content of eutectic structure is increased gradually. From the surface to bonding zone of coatings, the distribution of the mixing entropy changes from high entropy to medium entropy. With the addition of silicon, the microhardness and high-temperature oxidation at 900℃ of coatings are increased. When x is 1.0 mole, both the microhardness and the high-temperature oxidation resistance are the highest.
MoFeCrTiWSix (x=0, 0.2, 0.4, 0.6, 0.8, 1.0) multi-principal element alloy coatings were fabricated on Q235 steel by laser cladding. The effect of silicon on the microstructure, phases, microhardness and high-temperature oxidation resistance were investigated systematically by X-ray diffraction (XRD), scanning electron microscopy (SEM) and microhardness tester etc. The results show that, the phase of laser cladding MoFeCrTiW multi-principal element alloy coating is single BCC structure and its microstructure is equiaxed grains. The main phase is still BCC structure after adding different content of silicon into coating. When the content of silicon is no less than 0.4 moles, there exits small intermetallic compound in the coatings, the microstructures of coatings are composed of proeutectic BCC phase and eutectic structure of BCC phase and Cr5Fe50Mo8.9Si5.2Ti20.4 phase. With the content of silicon increasing, the morphology of proeutectic phase changes from cystiform-dendritic to columnar dendrites and equiaxed dendrites, while the content of eutectic structure is increased gradually. From the surface to bonding zone of coatings, the distribution of the mixing entropy changes from high entropy to medium entropy. With the addition of silicon, the microhardness and high-temperature oxidation at 900℃ of coatings are increased. When x is 1.0 mole, both the microhardness and the high-temperature oxidation resistance are the highest.
2017, 46(12):3947-3952.
Abstract:
A simple approach was proposed to fabricate tungsten carbides/graphitic carbon（WxC/GC） composites by using ion-exchange resin as carbon resource，ammonium metatungstate(AMT) as tungsten source and the potassium ferrocyanide（K4Fe(CN)6·3H2O）as catalyst. The resin-based precursor was prepared via the ion-exchange method and underwent reduction and synchronous carbonization at high temperature under N2 atmosphere to fabricate WxC/GC composites. Furthermore, the WxC/GC supported platinum nanoparticle (Pt/WxC/GC) was prepared by microwave-assisted polyol method. The crystalline phase，structure and morphology of samples were characterized with X—ray diffraction(XRD)，transmission electronic microscope(TEM)，and energy dispersive X-ray spectroscopy(EDS)．The electro-catalytic activity of Pt/WxC/GC in acidic media was investigated using cyclic voltammetry. The results indicated that WxC particles were uniformly distributed in the as-synthesized WxC/GC composites with the size of 2～30nm. Pt/WxC/GC with 10wt% Pt exhibits attractive catalytic activity and stability, the oxidation current density of methanol can reach 39mA·cm-2.
A simple approach was proposed to fabricate tungsten carbides/graphitic carbon（WxC/GC） composites by using ion-exchange resin as carbon resource，ammonium metatungstate(AMT) as tungsten source and the potassium ferrocyanide（K4Fe(CN)6·3H2O）as catalyst. The resin-based precursor was prepared via the ion-exchange method and underwent reduction and synchronous carbonization at high temperature under N2 atmosphere to fabricate WxC/GC composites. Furthermore, the WxC/GC supported platinum nanoparticle (Pt/WxC/GC) was prepared by microwave-assisted polyol method. The crystalline phase，structure and morphology of samples were characterized with X—ray diffraction(XRD)，transmission electronic microscope(TEM)，and energy dispersive X-ray spectroscopy(EDS)．The electro-catalytic activity of Pt/WxC/GC in acidic media was investigated using cyclic voltammetry. The results indicated that WxC particles were uniformly distributed in the as-synthesized WxC/GC composites with the size of 2～30nm. Pt/WxC/GC with 10wt% Pt exhibits attractive catalytic activity and stability, the oxidation current density of methanol can reach 39mA·cm-2.
2017, 46(12):3953-3960.
Abstract:
In order to improve high temperature oxidation resistance of niobium alloy, electroless plating combined with pack cementation technologies was used to obtain composite coatings with or without CeO2 particles. The microstructure and high temperature oxidation resistance of the composite coatings were investigated. Al/Ni coating contains NiAl phase, while Al/Ni-CeO2 coating is made up of NiAl, NiAl3, Al3Nb and CeO2, etc. The oxidation test of the composite coatings was carried out at 1000℃. The results show after 50 h oxidation mass gain of the Al/Ni composite coating was 8.0 mg/cm2, with the formation of Al2O3 and AlNbO4 phase; The mass gain of the Al/Ni-CeO2 composite coating after 50 h oxidation was 4.0 mg/cm2, with Al2O3, CeO2, NiAl, NiAl3, Al3Nb and AlNbO4 phase. On the surface of two coating systems continuous dense Al2O3 scales were detected with good adhesion to the coating. CeO2 particles were mainly aggregated in the interdiffusion zone under the drag force of Ni. The addition of CeO2 particles refines the coating structure, reduces the consumption of Al element in the coating, fills the holes, and enhances the adhesion of the scales to the coating, so as to improve the oxidation resistance of the coating.
In order to improve high temperature oxidation resistance of niobium alloy, electroless plating combined with pack cementation technologies was used to obtain composite coatings with or without CeO2 particles. The microstructure and high temperature oxidation resistance of the composite coatings were investigated. Al/Ni coating contains NiAl phase, while Al/Ni-CeO2 coating is made up of NiAl, NiAl3, Al3Nb and CeO2, etc. The oxidation test of the composite coatings was carried out at 1000℃. The results show after 50 h oxidation mass gain of the Al/Ni composite coating was 8.0 mg/cm2, with the formation of Al2O3 and AlNbO4 phase; The mass gain of the Al/Ni-CeO2 composite coating after 50 h oxidation was 4.0 mg/cm2, with Al2O3, CeO2, NiAl, NiAl3, Al3Nb and AlNbO4 phase. On the surface of two coating systems continuous dense Al2O3 scales were detected with good adhesion to the coating. CeO2 particles were mainly aggregated in the interdiffusion zone under the drag force of Ni. The addition of CeO2 particles refines the coating structure, reduces the consumption of Al element in the coating, fills the holes, and enhances the adhesion of the scales to the coating, so as to improve the oxidation resistance of the coating.
2017, 46(12):3961-3966.
Abstract:
Researched the corrosion behavior of TZM and La doped TZM alloy in acid and alkaline medium. Designed four corrosion period stages as 10days, 30days, 50days, 70days for respectively. Investigated and compared mass loss condition, weight loss condition, average corrosion rate and corrosion morphology. Anlysis the corrosion mechanism in acid and alkaline of TZM alloy and the effect of La doped on corrosion resistance of TZM alloy. The study shows TZM alloy corroded in acid major set off cell reaction and anode dissolved while cathode hydrogen evolution. Corrosion prior occurred at surface defect, impurty, grain boundary and dislocation. Crevice corrosion morphology was observed at the narrow slit which formed by scratch and width less than 0.0001 inch (0.025~0.1mm). Corrosion hardly occurred in alkaline medium. La doping could slightly rising the corrosion resistance of TZM alloy, but the improvement is not significant
Researched the corrosion behavior of TZM and La doped TZM alloy in acid and alkaline medium. Designed four corrosion period stages as 10days, 30days, 50days, 70days for respectively. Investigated and compared mass loss condition, weight loss condition, average corrosion rate and corrosion morphology. Anlysis the corrosion mechanism in acid and alkaline of TZM alloy and the effect of La doped on corrosion resistance of TZM alloy. The study shows TZM alloy corroded in acid major set off cell reaction and anode dissolved while cathode hydrogen evolution. Corrosion prior occurred at surface defect, impurty, grain boundary and dislocation. Crevice corrosion morphology was observed at the narrow slit which formed by scratch and width less than 0.0001 inch (0.025~0.1mm). Corrosion hardly occurred in alkaline medium. La doping could slightly rising the corrosion resistance of TZM alloy, but the improvement is not significant
2017, 46(12):3967-3971.
Abstract:
Both of the α′ and α+α′ martensite microstructures of Ti60 alloy as high temperature titanium alloy used up to 600°C can be obtained by solution treatments at different temperatures. The morphologies of the two microsturctures are compared as well as the tensile properties at room temperature, 300°C and 600°C. The results indicate that all the β phase transforms to α′ phase during quenching, and only about 10% primary α phase retains in the α+α′ microstructure. The little decrease of strength and great increase of ductility can be attributed to the partial solution of primary α phase. The size of dimple observed on the fracture of specimens with α+α′ microstructure at room temperature is larger than that with α′ microstructure. Because the retained primary α phase dedicates to the refinement of β grains, leading to the disturbance of expansion of cracks by increasing the length of grain boundaries. The influence of the primary α phase on the tensile properties decreases with the increasing of the tensile temperature.
Both of the α′ and α+α′ martensite microstructures of Ti60 alloy as high temperature titanium alloy used up to 600°C can be obtained by solution treatments at different temperatures. The morphologies of the two microsturctures are compared as well as the tensile properties at room temperature, 300°C and 600°C. The results indicate that all the β phase transforms to α′ phase during quenching, and only about 10% primary α phase retains in the α+α′ microstructure. The little decrease of strength and great increase of ductility can be attributed to the partial solution of primary α phase. The size of dimple observed on the fracture of specimens with α+α′ microstructure at room temperature is larger than that with α′ microstructure. Because the retained primary α phase dedicates to the refinement of β grains, leading to the disturbance of expansion of cracks by increasing the length of grain boundaries. The influence of the primary α phase on the tensile properties decreases with the increasing of the tensile temperature.
2017, 46(12):3972-3976.
Abstract:
The nternational thermonuclear experimental reactor (ITER) project W-Cu divertor component model was made by hot isostatic pressing (HIP) diffusion welding method under three HIP diffusion welding processes with the temperature of 950℃, 980℃ and 1050℃ respectively，and the model is studied by analyzing a module using the magnetron sputtering method to deposit a 40μm-thick copper coating as the interlayer. This paper aims to study effect of the magnetron sputtering method to deposit a 40μm-thick copper coating as the interlayer of W-Cu divertor component model properties. The morphology and composition of the tungsten and Cu-Cr-Zr alloy joints investigated by SEM and EDS, the joint defects were detected by ultrasonic non-destructive testing(NDT) equipment, the bond strength of joints were mearsured by mechanical tensile tester. The results show that magnetron sputtering method to deposit a 40μm-thick copper coating as the interlayer,it can significantly help to improve properties of Hot Isostatic Pressing Joining. Especially at 980 ℃, the welding module is fully prepared to meet the requirements of the ITER divertor.
The nternational thermonuclear experimental reactor (ITER) project W-Cu divertor component model was made by hot isostatic pressing (HIP) diffusion welding method under three HIP diffusion welding processes with the temperature of 950℃, 980℃ and 1050℃ respectively，and the model is studied by analyzing a module using the magnetron sputtering method to deposit a 40μm-thick copper coating as the interlayer. This paper aims to study effect of the magnetron sputtering method to deposit a 40μm-thick copper coating as the interlayer of W-Cu divertor component model properties. The morphology and composition of the tungsten and Cu-Cr-Zr alloy joints investigated by SEM and EDS, the joint defects were detected by ultrasonic non-destructive testing(NDT) equipment, the bond strength of joints were mearsured by mechanical tensile tester. The results show that magnetron sputtering method to deposit a 40μm-thick copper coating as the interlayer,it can significantly help to improve properties of Hot Isostatic Pressing Joining. Especially at 980 ℃, the welding module is fully prepared to meet the requirements of the ITER divertor.
2017, 46(12):3977-3982.
Abstract:
Using ammonium metatungstate, soluble cobalt salt, soluble carbon as the raw materials, ultrafine WC-Co composite powder was synthesized by spraying conversion, calcination, in-situ reduction and carbonization route. The composite powder fabricated by the similar route, only increased a short-time ball milling process after the calcination, was more disperse. Ultrafine WC-Co cemented carbides were prepared by spark plasma sintering with this two kinds of powders. The morphology, microstructure and mechanical properties of composite powders and cemented carbides were characterized by SEM, XRD, Vickers hardness tester and so on . The results show that the composite powder fabricated via the route without short-time ball milling process is spherical and has obvious sintering characteristics. WC particles are bonded together, the sintering neck and abnormal grain growth can be observed obviously. Powder fabricated via the route with a short-time ball milling process is more disperse. The fcc-Co and hcp-Co were existed in all two kinds of powders, the grain size of WC is 0.26 μm. There are a few pores exists in the alloy prepared by the spherical composited powder. The density is lower and the WC has abnormal growth. The mechanical properties of the alloy prepared by the dispersed composite powder are better.
Using ammonium metatungstate, soluble cobalt salt, soluble carbon as the raw materials, ultrafine WC-Co composite powder was synthesized by spraying conversion, calcination, in-situ reduction and carbonization route. The composite powder fabricated by the similar route, only increased a short-time ball milling process after the calcination, was more disperse. Ultrafine WC-Co cemented carbides were prepared by spark plasma sintering with this two kinds of powders. The morphology, microstructure and mechanical properties of composite powders and cemented carbides were characterized by SEM, XRD, Vickers hardness tester and so on . The results show that the composite powder fabricated via the route without short-time ball milling process is spherical and has obvious sintering characteristics. WC particles are bonded together, the sintering neck and abnormal grain growth can be observed obviously. Powder fabricated via the route with a short-time ball milling process is more disperse. The fcc-Co and hcp-Co were existed in all two kinds of powders, the grain size of WC is 0.26 μm. There are a few pores exists in the alloy prepared by the spherical composited powder. The density is lower and the WC has abnormal growth. The mechanical properties of the alloy prepared by the dispersed composite powder are better.
2017, 46(12):3983-3988.
Abstract:
Elements diffusion across the interface will result in poor performance during service, so it’s important to put a barrier layer between thermoelectric materials and electrode, and get them bonded perfectly as well. In this work, with copper as electrode and nickel foil as barrier layer, Cu/Ni/Mg2Si thermoelectric joint was prepared by the field-activated pressure-assisted synthesis (FAPAS) method, in which the in situ synthesis of Mg2Si and bonding between different layers were accomplished in one step. SEM, EDS and XRD were used to observe the microstructure, determine phase component and forming process of new phases, and obtain element distribution across the interface; thermal shock test and four probe method were used to evaluate the mechanical properties and electrical resistivity of the joint. The results show that the synthesized Mg2Si has high purity and stable coefficient of thermal expansion (CTE) at high temperatures. The nickel layer blocks the mutual element diffusion effectively in interface and gets bonded well with copper and the synthesized Mg2Si, respectively, accompanied by the formation of new phase, Mg2SiNi3 and Mg2Ni, in turn in the former interface. Based on good match of CTE in Cu/Ni/Mg2Si interfaces, the joint stays intact even experiencing 60 thermal shock cycles. With the increase of aging time, the thickness of interfacial diffusion layer gets wider, and the contact resistance increases subsequently, which roughly fits the linear relation with . The minimum contact resistivity of the joint is 112 μΩ?cm2 when the bonding temperature is 700℃.
Elements diffusion across the interface will result in poor performance during service, so it’s important to put a barrier layer between thermoelectric materials and electrode, and get them bonded perfectly as well. In this work, with copper as electrode and nickel foil as barrier layer, Cu/Ni/Mg2Si thermoelectric joint was prepared by the field-activated pressure-assisted synthesis (FAPAS) method, in which the in situ synthesis of Mg2Si and bonding between different layers were accomplished in one step. SEM, EDS and XRD were used to observe the microstructure, determine phase component and forming process of new phases, and obtain element distribution across the interface; thermal shock test and four probe method were used to evaluate the mechanical properties and electrical resistivity of the joint. The results show that the synthesized Mg2Si has high purity and stable coefficient of thermal expansion (CTE) at high temperatures. The nickel layer blocks the mutual element diffusion effectively in interface and gets bonded well with copper and the synthesized Mg2Si, respectively, accompanied by the formation of new phase, Mg2SiNi3 and Mg2Ni, in turn in the former interface. Based on good match of CTE in Cu/Ni/Mg2Si interfaces, the joint stays intact even experiencing 60 thermal shock cycles. With the increase of aging time, the thickness of interfacial diffusion layer gets wider, and the contact resistance increases subsequently, which roughly fits the linear relation with . The minimum contact resistivity of the joint is 112 μΩ?cm2 when the bonding temperature is 700℃.
2017, 46(12):3989-3993.
Abstract:
In this paper, the fine silver, silver-graphite and fine silver/silver graphite composite coatings were prepared on copper substrate by the electro-deposition method. The influence of treatment temperature on the contact resistance of three types of composite coating was particularly investigated. At room temperature, the contact resistance of the composite coatings has lower than that of the fine silver coating under the same torque. After heat treatment from 25 ℃ to 240 ℃, there are no significant differences of contact resistance for three types of coating. With the increase of treatment temperature from 240 ℃ to 600 ℃, the contact resistance of the fine silver coating and silver/silver-graphite composite coating gradually increased, and achieved the values of 54.3 μΩ and 42.6 μΩ under the 5 N m torque, respectively. However, the contact resistance of the silver-graphite composite coating rapidly increased with treatment temperature from 240 ℃ to 600 ℃, and achieved the values of 125.5 μΩ at 480 ℃ with the phenomenon of serious desquamate on the coating surface.
In this paper, the fine silver, silver-graphite and fine silver/silver graphite composite coatings were prepared on copper substrate by the electro-deposition method. The influence of treatment temperature on the contact resistance of three types of composite coating was particularly investigated. At room temperature, the contact resistance of the composite coatings has lower than that of the fine silver coating under the same torque. After heat treatment from 25 ℃ to 240 ℃, there are no significant differences of contact resistance for three types of coating. With the increase of treatment temperature from 240 ℃ to 600 ℃, the contact resistance of the fine silver coating and silver/silver-graphite composite coating gradually increased, and achieved the values of 54.3 μΩ and 42.6 μΩ under the 5 N m torque, respectively. However, the contact resistance of the silver-graphite composite coating rapidly increased with treatment temperature from 240 ℃ to 600 ℃, and achieved the values of 125.5 μΩ at 480 ℃ with the phenomenon of serious desquamate on the coating surface.
2017, 46(12):3994-3999.
Abstract:
Niobium acts as a main alloying element in the third generation zirconium alloys. The role of Nb element in the alloys is greatly concerned. The influences of Nb content on the microstructure and recrystallization process of Zr-xNb (x=0, 0.3, 0.7, 1.0) alloys were studied by means of transmission electron microscopy (TEM), optical microscopy (OM) and Vickers micro-hardness testing. The results show that with increasing Nb content the quantity of the precipitates increases and the mean size of the precipitate particles decreases. Meanwhile, the recrystallization process is slowed down by the precipitates, especially in the case of Zr-1Nb alloy. The main precipitates were found to be Zr(Nb,Fe,Cr)2 and β-Nb in Zr-0.3Nb and Zr-1Nb, respectively.
Niobium acts as a main alloying element in the third generation zirconium alloys. The role of Nb element in the alloys is greatly concerned. The influences of Nb content on the microstructure and recrystallization process of Zr-xNb (x=0, 0.3, 0.7, 1.0) alloys were studied by means of transmission electron microscopy (TEM), optical microscopy (OM) and Vickers micro-hardness testing. The results show that with increasing Nb content the quantity of the precipitates increases and the mean size of the precipitate particles decreases. Meanwhile, the recrystallization process is slowed down by the precipitates, especially in the case of Zr-1Nb alloy. The main precipitates were found to be Zr(Nb,Fe,Cr)2 and β-Nb in Zr-0.3Nb and Zr-1Nb, respectively.
2017, 46(12):4000-4005.
Abstract:
Thermal oxidation (TO) process was applied to treat TC4 alloy. Microstructural characteristics of the TO layer were analyzed using scanning electron microscope (SEM), energy dispersive spectrometer (EDS), optical microscope (OM), glow discharge optical emission spectrometer analysis (GDOES) and X-ray diffraction (XRD). Erosive wear behaviors of the TO treated TC4 alloy in CO2-saturated simulated oilfield medium were investigated. The results showed that the obtained TO layer was mainly composed of rutile TiO2 phase. The TO layer presented higher surface hardness and lower mass loss values. TO treatment had significantly improve the resistance to erosive wear of TC4 alloy.
Thermal oxidation (TO) process was applied to treat TC4 alloy. Microstructural characteristics of the TO layer were analyzed using scanning electron microscope (SEM), energy dispersive spectrometer (EDS), optical microscope (OM), glow discharge optical emission spectrometer analysis (GDOES) and X-ray diffraction (XRD). Erosive wear behaviors of the TO treated TC4 alloy in CO2-saturated simulated oilfield medium were investigated. The results showed that the obtained TO layer was mainly composed of rutile TiO2 phase. The TO layer presented higher surface hardness and lower mass loss values. TO treatment had significantly improve the resistance to erosive wear of TC4 alloy.
2017, 46(12):4006-4011.
Abstract:
Four simple methods of fabricating a super-hydrophobic film on magnesium alloy through the employment of two chemical reagents and two surface modifiers are reported in the paper. The Mg alloys are chemically etched by CuCl2 or ZnSO4 first and then modified with low surface energy material of oleic acid or stearic acid. After modification, the obtained samples show super-hydrophobicity with static contact angle to reach more than 150 ° and the sliding angle of about 6.5 °. The super-hydrophobicity of obtained samples are stable; the water contact angle remains above 150 ° after being exposed in air for six months. Compared with the electrochemical properties of four super-hydrophobic samples, it can be found that the sample that is etched by CuCl2 and then self-assembled by stearic acid has the best corrosion resistance with the corrosion potential Ecorr improved by 0.33V, reaching to -1.11V. The diameter of capacitive arc is also 6-7 times than substrate.
Four simple methods of fabricating a super-hydrophobic film on magnesium alloy through the employment of two chemical reagents and two surface modifiers are reported in the paper. The Mg alloys are chemically etched by CuCl2 or ZnSO4 first and then modified with low surface energy material of oleic acid or stearic acid. After modification, the obtained samples show super-hydrophobicity with static contact angle to reach more than 150 ° and the sliding angle of about 6.5 °. The super-hydrophobicity of obtained samples are stable; the water contact angle remains above 150 ° after being exposed in air for six months. Compared with the electrochemical properties of four super-hydrophobic samples, it can be found that the sample that is etched by CuCl2 and then self-assembled by stearic acid has the best corrosion resistance with the corrosion potential Ecorr improved by 0.33V, reaching to -1.11V. The diameter of capacitive arc is also 6-7 times than substrate.
2017, 46(12):4012-4020.
Abstract:
Single-walled carbon nanotubes (SWNTs) are the ideal candidates for making next-generation electronic circuits because of their high strength, high toughness, high thermal stability, and superior electrical conductivity . However, achieving these goals is extremely challenging because the as-grown SWNTs contains mixtures of semiconducting (s-) and metallic- (m-) SWNTs, typically inadequate for integrated circuits. How to separate these two spcies according to their electronic structure and chemical activity has attracted much recent attention. Herein, this review focuses on the “in situ” metheds and techniques for the selective growth of s- and m-SWNT. Based on the understanding of the growth mechanism of those strategies, we try to propose the general guideline on that how can we develop the optimal condition for large-scaled growth of s- and m-SWNTs.
Single-walled carbon nanotubes (SWNTs) are the ideal candidates for making next-generation electronic circuits because of their high strength, high toughness, high thermal stability, and superior electrical conductivity . However, achieving these goals is extremely challenging because the as-grown SWNTs contains mixtures of semiconducting (s-) and metallic- (m-) SWNTs, typically inadequate for integrated circuits. How to separate these two spcies according to their electronic structure and chemical activity has attracted much recent attention. Herein, this review focuses on the “in situ” metheds and techniques for the selective growth of s- and m-SWNT. Based on the understanding of the growth mechanism of those strategies, we try to propose the general guideline on that how can we develop the optimal condition for large-scaled growth of s- and m-SWNTs.
