Volume 45,Issue 2,2016 Table of Contents
2016, 45(2):261-266.
Abstract:
A simple and environmentally friendly method was developed for preparing colloidal silver nanoparticels in aqueous solutions using silver nitrate, sodium alginate and glucose as silver precursor, capping agents and reducing agents respectively. The formation of silver nanoparticles was observed by change of color from colorless to yellow. The silver nanoparticles were characterized by transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis) and X-ray diffraction (XRD). The TEM images showed that, the particles are small, well dispersed and spherical in shape with a narrow distribution from 3 nm to 12 nm. The XRD demonstrated that the obtained metallic nanoparticles are single crystalline silver nanoparticles. The effects of the reaction time, reaction temperature and the concentration of silver ion and reducing agent on the particle size were investigated by the UV-vis spectra. The present process is an excellent candidate for the preparation of silver nanoparticles because it is simple, pollutant free, inexpensive and easy to perform. The method may be extended to other noble metals, such as Au, Pd and Pt, for medicinal, industrial and technological applications.
A simple and environmentally friendly method was developed for preparing colloidal silver nanoparticels in aqueous solutions using silver nitrate, sodium alginate and glucose as silver precursor, capping agents and reducing agents respectively. The formation of silver nanoparticles was observed by change of color from colorless to yellow. The silver nanoparticles were characterized by transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis) and X-ray diffraction (XRD). The TEM images showed that, the particles are small, well dispersed and spherical in shape with a narrow distribution from 3 nm to 12 nm. The XRD demonstrated that the obtained metallic nanoparticles are single crystalline silver nanoparticles. The effects of the reaction time, reaction temperature and the concentration of silver ion and reducing agent on the particle size were investigated by the UV-vis spectra. The present process is an excellent candidate for the preparation of silver nanoparticles because it is simple, pollutant free, inexpensive and easy to perform. The method may be extended to other noble metals, such as Au, Pd and Pt, for medicinal, industrial and technological applications.
2016, 45(2):267-271.
Abstract:
Mn55Al45 alloy was prepared by the combined use of arc melting, high energy ball milling and tempering heat treatment process. The phase structure and the microstructure of the alloy powders were analyzed by X-ray diffraction(XRD) and scanning electron microscopy(SEM), then their microwave absorbing properties were analyzed by vector network analyzer. The results show that an increase of phase for Al2Mn3 and Al11Mn14 are accompanied by the increased milling time; the resonant frequency and absorption peak of ε″ and μ″ shifts towards lower frequency region simultaneously. A better result of electromagnetic properties was brought to the alloy powders when the ball milling time was set to 18 hours in first attempt. While the ball milling time was increased to 24 hours during later experiment, the minimum reflectivity value reached to -28 dB at a frequency of 16 GHz. The Al2Mn3 phase increase with an artificial increases of tempering temperature. The Mn55Al45 alloy dealt with 18 h ball milling time under 400 ℃ heat treatment exhibits preferably comprehensive microwave absorbing properties in the range of 6-18 GHz. The minimum reflectivity value and absorption peak frequency with the coating thickness of 2.0 mm, are -26.4 dB, 17 GHz respectively.
Mn55Al45 alloy was prepared by the combined use of arc melting, high energy ball milling and tempering heat treatment process. The phase structure and the microstructure of the alloy powders were analyzed by X-ray diffraction(XRD) and scanning electron microscopy(SEM), then their microwave absorbing properties were analyzed by vector network analyzer. The results show that an increase of phase for Al2Mn3 and Al11Mn14 are accompanied by the increased milling time; the resonant frequency and absorption peak of ε″ and μ″ shifts towards lower frequency region simultaneously. A better result of electromagnetic properties was brought to the alloy powders when the ball milling time was set to 18 hours in first attempt. While the ball milling time was increased to 24 hours during later experiment, the minimum reflectivity value reached to -28 dB at a frequency of 16 GHz. The Al2Mn3 phase increase with an artificial increases of tempering temperature. The Mn55Al45 alloy dealt with 18 h ball milling time under 400 ℃ heat treatment exhibits preferably comprehensive microwave absorbing properties in the range of 6-18 GHz. The minimum reflectivity value and absorption peak frequency with the coating thickness of 2.0 mm, are -26.4 dB, 17 GHz respectively.
3 Direct Electrochemical Formation of different phases Al–Y Alloys by codeposition in LiCl–KCl Melts
2016, 45(2):272-276.
Abstract:
Electrochemical preparation of different phases Al–Y alloys were investigated in LiCl–KCl–AlCl3–Y2O3 melts at 773 K by cyclic voltammetry, square wave voltammetry, open circuit chronopotentiometry, and polarization curve. These electrochemical measurements showed that the underpotential deposition (UPD) of yttrium on pre-deposited Al forms two Al–Y intermetallic compounds. The results of X-ray diffraction (XRD) analysis indicate that the two differrent Al–Y intermetallic compounds are Al2Y and α-Al3Y. The microstructure and micro-zone chemical analysis of Al–Y alloys were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), respectively. The results illustrate that element Y mainly distributes on nubby precipitates. Different phases Al–Y Alloys can be obtained by adjusting the concentration of AlCl3.
Electrochemical preparation of different phases Al–Y alloys were investigated in LiCl–KCl–AlCl3–Y2O3 melts at 773 K by cyclic voltammetry, square wave voltammetry, open circuit chronopotentiometry, and polarization curve. These electrochemical measurements showed that the underpotential deposition (UPD) of yttrium on pre-deposited Al forms two Al–Y intermetallic compounds. The results of X-ray diffraction (XRD) analysis indicate that the two differrent Al–Y intermetallic compounds are Al2Y and α-Al3Y. The microstructure and micro-zone chemical analysis of Al–Y alloys were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), respectively. The results illustrate that element Y mainly distributes on nubby precipitates. Different phases Al–Y Alloys can be obtained by adjusting the concentration of AlCl3.
2016, 45(2):277-281.
Abstract:
Polycrystalline bulk samples Zn0.98Fe0.02O doped with additional Sn or Cu have been fabricated at 600oC by a coprecipitation method. The XRD structure analysis shows that all samples are of single phase with the ZnO-like wurtzite structure. X-ray photoelectron spectroscopy indicates an oxidation state of 4 for Sn，while a mixed state of 1 and 2 for Cu. It is found that Zn0.98Fe0.02O without additional doping shows weak ferromagnetism at room temperature. Cu doping has induced a light increase of magnetization in low temperature of 10 K, while Sn doping has seriously suppressed the ferromagnetism in whole temperature range. This result is consistent with bound magnetic polaron model relative to hole carriers.
Polycrystalline bulk samples Zn0.98Fe0.02O doped with additional Sn or Cu have been fabricated at 600oC by a coprecipitation method. The XRD structure analysis shows that all samples are of single phase with the ZnO-like wurtzite structure. X-ray photoelectron spectroscopy indicates an oxidation state of 4 for Sn，while a mixed state of 1 and 2 for Cu. It is found that Zn0.98Fe0.02O without additional doping shows weak ferromagnetism at room temperature. Cu doping has induced a light increase of magnetization in low temperature of 10 K, while Sn doping has seriously suppressed the ferromagnetism in whole temperature range. This result is consistent with bound magnetic polaron model relative to hole carriers.
2016, 45(2):282-286.
Abstract:
By improving the method of glass denucleating combined with cycle superheating based on traditional undercooling method, a stable undercooling above 200 K of 100g bulk K4169 is obtained, and the largest undercooling goes to 281 K. The effect of denucleating agent and superheating have been discussed. Moreover, the three-dimensional numerical analysis of temperature field inside the undercooled melt is presented, it can be found that the maximum temperature deviation in different parts is only 14K before nucleation. In contrast with the as-solidified microstructure, the grain size will increase with the increment of nucleating temperature. But the difference of microstructure is tiny and the average grain size is 12?2 μm.
By improving the method of glass denucleating combined with cycle superheating based on traditional undercooling method, a stable undercooling above 200 K of 100g bulk K4169 is obtained, and the largest undercooling goes to 281 K. The effect of denucleating agent and superheating have been discussed. Moreover, the three-dimensional numerical analysis of temperature field inside the undercooled melt is presented, it can be found that the maximum temperature deviation in different parts is only 14K before nucleation. In contrast with the as-solidified microstructure, the grain size will increase with the increment of nucleating temperature. But the difference of microstructure is tiny and the average grain size is 12?2 μm.
2016, 45(2):287-291.
Abstract:
Microstructure, age hardening response and mechanical properties of Mg-4.0Sm-xCa (x=0.5, 1.0 and 1.5 wt%) alloys during extrusion and subsequent isothermal aging at 200 oC were investigated. The results indicate that with the addition of Ca, the bulk and particle-like Mg41Sm5 phases containing Ca and the needle/rod-like Mg2Ca phases form in the Mg matrix, grains of the alloy are refined and tensile mechanical properties are improved remarkably. In T5 (peak-aging) condition, the Mg-4.0Sm-1.0Ca alloy shows the smallest grain size of 5.1 μm. The amount of Mg2Ca phase increases gradually, but that of the bulk Ca-containing Mg41Sm5 phase in alloy with 1.5 wt% Ca significantly decrease, which mainly distribute at the grain boundaries. The peak-aged Mg-4.0Sm -1.0Ca alloy exhibits the highest peak hardness (82 HV) and the optimal ultimate tensile strength, yield tensile strength and elongation of 267 MPa, 189 MPa and 24%, respectively. The improved mechanical properties of the alloy are attributed to grain refinement, solution strengthening and precipitation strengthening of Mg2Ca phase and Mg41Sm5 phase.
Microstructure, age hardening response and mechanical properties of Mg-4.0Sm-xCa (x=0.5, 1.0 and 1.5 wt%) alloys during extrusion and subsequent isothermal aging at 200 oC were investigated. The results indicate that with the addition of Ca, the bulk and particle-like Mg41Sm5 phases containing Ca and the needle/rod-like Mg2Ca phases form in the Mg matrix, grains of the alloy are refined and tensile mechanical properties are improved remarkably. In T5 (peak-aging) condition, the Mg-4.0Sm-1.0Ca alloy shows the smallest grain size of 5.1 μm. The amount of Mg2Ca phase increases gradually, but that of the bulk Ca-containing Mg41Sm5 phase in alloy with 1.5 wt% Ca significantly decrease, which mainly distribute at the grain boundaries. The peak-aged Mg-4.0Sm -1.0Ca alloy exhibits the highest peak hardness (82 HV) and the optimal ultimate tensile strength, yield tensile strength and elongation of 267 MPa, 189 MPa and 24%, respectively. The improved mechanical properties of the alloy are attributed to grain refinement, solution strengthening and precipitation strengthening of Mg2Ca phase and Mg41Sm5 phase.
2016, 45(2):292-296.
Abstract:
The cerium modified 0.9Bi4Ti3O12–0.1K0.5Na0.5NbO3 (BTO-KNN) piezoelectric ceramics were synthesized using conventional solid state processing. The effects of cerium addition on the microstructure and electrical properties of BTO-KNN ceramics had been investigated in details. It was found that the ceramics possess a pure phase of bismuth oxide layer-type structure. The piezoelectric properties of BTO-KNN–based ceramics were significantly enhanced after cerium doping. The piezoelectric constant d33, dielectric loss tan δ, mechanical quality factor Qm and remanent polarization Pr for the BTO-KNN ceramics with 0.75 wt% CeO2 modification were found to be 28 pC/N, 0.29%, 2897, 11.83 μC/cm2, respectively, together with the high Tc ( ~ 615 °C) and stable piezoelectric properties, demonstrating that the cerium modified BTO-KNN piezoelectric ceramics are the promising candidates for high–temperature applications.
The cerium modified 0.9Bi4Ti3O12–0.1K0.5Na0.5NbO3 (BTO-KNN) piezoelectric ceramics were synthesized using conventional solid state processing. The effects of cerium addition on the microstructure and electrical properties of BTO-KNN ceramics had been investigated in details. It was found that the ceramics possess a pure phase of bismuth oxide layer-type structure. The piezoelectric properties of BTO-KNN–based ceramics were significantly enhanced after cerium doping. The piezoelectric constant d33, dielectric loss tan δ, mechanical quality factor Qm and remanent polarization Pr for the BTO-KNN ceramics with 0.75 wt% CeO2 modification were found to be 28 pC/N, 0.29%, 2897, 11.83 μC/cm2, respectively, together with the high Tc ( ~ 615 °C) and stable piezoelectric properties, demonstrating that the cerium modified BTO-KNN piezoelectric ceramics are the promising candidates for high–temperature applications.
2016, 45(2):297-302.
Abstract:
VC (Vanadium Carbide) coating was prepared on the substrate surface of Cr12MoV from the raw materials such as anhydrous borate, FeV50, FeSi45 and etc. by TD (Thermal Diffusion) process, the coating structures and chemical element contributions were characterized with SEM (Scanning Electron Microscope), XRD (X-ray Diffraction), XPS (X-ray Photoelectron Spectroscopy) and EDS (Energy Dispersive Spectrometer), respectively. The chemical element distributions of VC coating surface and interface was analyzed with plane scan of energy-dispersive spectroscopy, and the mechanism of interfacial metallurgical combine was discussed. The results show that VC coating is a compound, consisted of C and V elements, and the V atom concentration is twice as that of atom; VC coating is the single VC phase, the electron binding energy of V element is located at 512.8eV, and that of C element is located at 282.2eV; There were diffused between V, C and Fe elements each other in the coating interface, forming a interface diffusion layer, the interface of VC coating-substrate is combined with the metallurgical combine.
VC (Vanadium Carbide) coating was prepared on the substrate surface of Cr12MoV from the raw materials such as anhydrous borate, FeV50, FeSi45 and etc. by TD (Thermal Diffusion) process, the coating structures and chemical element contributions were characterized with SEM (Scanning Electron Microscope), XRD (X-ray Diffraction), XPS (X-ray Photoelectron Spectroscopy) and EDS (Energy Dispersive Spectrometer), respectively. The chemical element distributions of VC coating surface and interface was analyzed with plane scan of energy-dispersive spectroscopy, and the mechanism of interfacial metallurgical combine was discussed. The results show that VC coating is a compound, consisted of C and V elements, and the V atom concentration is twice as that of atom; VC coating is the single VC phase, the electron binding energy of V element is located at 512.8eV, and that of C element is located at 282.2eV; There were diffused between V, C and Fe elements each other in the coating interface, forming a interface diffusion layer, the interface of VC coating-substrate is combined with the metallurgical combine.
2016, 45(2):303-308.
Abstract:
The re-dissolution of zirconium diacetate- yttria shell (ZA-Y shell) and its impact were studied. The re-dissolution rate under hot water and steamin miosture condition was measured by the balance. Three-point flexural strength was measured using the universal testing machine, and the fracture index was calculated. The distribution of the surface precipitates was observed by Ooptical microscope was used to observe the distribution of the surface precipitates, and its morphology and composition were tested using scanning electron microscopy (SEM) combined with energy spectrum analysis (EDS). Composition of the ZA-Y shell was measured by X-ray fluorescence (XRF) method. The reason of the precipitates was analysed. The results suggest the re-dissolution is limited. The maximum water penetration rate is 2.5% and the dissolution rate is 0.8% in 20 min. The strength reduces 26% and fracture index reduces to 66%. The surface precipitates are due to dissolution of ammonium metatungstate (AMT) and own two reasons: drastictoo high pressure release or fast drying condition with slow heat dissipation.
The re-dissolution of zirconium diacetate- yttria shell (ZA-Y shell) and its impact were studied. The re-dissolution rate under hot water and steamin miosture condition was measured by the balance. Three-point flexural strength was measured using the universal testing machine, and the fracture index was calculated. The distribution of the surface precipitates was observed by Ooptical microscope was used to observe the distribution of the surface precipitates, and its morphology and composition were tested using scanning electron microscopy (SEM) combined with energy spectrum analysis (EDS). Composition of the ZA-Y shell was measured by X-ray fluorescence (XRF) method. The reason of the precipitates was analysed. The results suggest the re-dissolution is limited. The maximum water penetration rate is 2.5% and the dissolution rate is 0.8% in 20 min. The strength reduces 26% and fracture index reduces to 66%. The surface precipitates are due to dissolution of ammonium metatungstate (AMT) and own two reasons: drastictoo high pressure release or fast drying condition with slow heat dissipation.
2016, 45(2):309-314.
Abstract:
Sintered and aged Dy-doped NdFeB magnets was studied in this work. The magnetic properties, microstructures and compositions was investigated by hysteresis loop instrument, thermal field emission scanning electron microscopy and energy disperse spectroscopy, respectively. The result of analysis indicated that Dy element mainly distributed in the Nd-rich phase, Nd-Dy oxides and Dy-rich particles which is located at the grain boundary of the sintered magnets, in addition to the main crystal phase Nd2Fe14B. The optimized aging process is beneficial to promote a reasonable diffusion and distribution for Dy element. The Dy contents of Nd-riched phases, Nd-Dy oxide, and Dy-riched particle decreased successively in the sintered, the high temperature aged and the optimal two-stage aged Dy-doped NdFeB permanent magnets. The measurements demonstrated that the enhancement of the coercivity of the aged Dy-doped NdFeB Magnet was caused mainly by the Dy element reasonable distribution.
Sintered and aged Dy-doped NdFeB magnets was studied in this work. The magnetic properties, microstructures and compositions was investigated by hysteresis loop instrument, thermal field emission scanning electron microscopy and energy disperse spectroscopy, respectively. The result of analysis indicated that Dy element mainly distributed in the Nd-rich phase, Nd-Dy oxides and Dy-rich particles which is located at the grain boundary of the sintered magnets, in addition to the main crystal phase Nd2Fe14B. The optimized aging process is beneficial to promote a reasonable diffusion and distribution for Dy element. The Dy contents of Nd-riched phases, Nd-Dy oxide, and Dy-riched particle decreased successively in the sintered, the high temperature aged and the optimal two-stage aged Dy-doped NdFeB permanent magnets. The measurements demonstrated that the enhancement of the coercivity of the aged Dy-doped NdFeB Magnet was caused mainly by the Dy element reasonable distribution.
2016, 45(2):315-320.
Abstract:
In this study, the alumina coatings as tritium permeation barrier were deposited on 316L stainless steel by plasma electrolytic oxidation. The effects of plasma electrolytic oxidation on the coatings by different parameters were investigated, and the phase, surface morphology, thickness were characterized by XRD, SEM and eddy current method respectively. After analyzing through scratch adhesion test, thermal shock resistance test and tritium permeability test, it obtains the optimized coatings. The results show that phase, surface morphology, thickness are affected by current density, voltage and PEO (plasma electrolytic oxidation) duration time. The current density and voltage can change the phase structure of coatings, higher current density propel the transformation of Al→Al2O3 and higher voltage propel the transformation of γ- Al2O3→α-Al2O3.With increasing voltage and duration time, the pore size becomes bigger and the quantity is less so that surface morphology is worse. With current density increasing to appropriate state (9A/dm2), surface morphology is good. The coatings thickness increases with increasing density, voltage and duration time. After a series of tests, the coatings, which were obtained at 6A/dm2, 300V, 30min, has the good performance with film-substrate cohesion (86.0N) , thermal shock resistance( the coatings changed little after 280 times tests) and the tritium permeation resistance of coated sample is improved 3 orders of magnitude higher than the 316Lstainless steel bulk.
In this study, the alumina coatings as tritium permeation barrier were deposited on 316L stainless steel by plasma electrolytic oxidation. The effects of plasma electrolytic oxidation on the coatings by different parameters were investigated, and the phase, surface morphology, thickness were characterized by XRD, SEM and eddy current method respectively. After analyzing through scratch adhesion test, thermal shock resistance test and tritium permeability test, it obtains the optimized coatings. The results show that phase, surface morphology, thickness are affected by current density, voltage and PEO (plasma electrolytic oxidation) duration time. The current density and voltage can change the phase structure of coatings, higher current density propel the transformation of Al→Al2O3 and higher voltage propel the transformation of γ- Al2O3→α-Al2O3.With increasing voltage and duration time, the pore size becomes bigger and the quantity is less so that surface morphology is worse. With current density increasing to appropriate state (9A/dm2), surface morphology is good. The coatings thickness increases with increasing density, voltage and duration time. After a series of tests, the coatings, which were obtained at 6A/dm2, 300V, 30min, has the good performance with film-substrate cohesion (86.0N) , thermal shock resistance( the coatings changed little after 280 times tests) and the tritium permeation resistance of coated sample is improved 3 orders of magnitude higher than the 316Lstainless steel bulk.
2016, 45(2):321-325.
Abstract:
The crack tip mechanical characteristic and crack propagation rates are influenced by crack length, but current research of environmentally assisted cracking (EAC) focuses on long crack and small crack is usually ignored. The mechanical characteristic nearby small crack tip for single-edge crack panel specimens during the EAC in high temperature water was studied, the specimens was made of nickel-base alloy and the finite element method was adopted. The results show that the stress and strain is much higher for small crack than that of long crack, and this lead to the higher crack propagation tendency of small crack. A corrected method is introduced to calculate the plastic zone size of small crack. The Irwin correction method can improve the accuracy of J integral of long crack, but errors still exists for small crack. So the numerical method with elastic plastic fracture method is recommended to calculated J integral for small crack under larger load condition considering the lack of mature theoretical guidance about the small crack. The crack propagation process of the EAC of structure materials serviced in nuclear power plants is suggested to divide into two small crack propagation and long crack propagation considering to the anomalous mechanical behavior of the small crack.
The crack tip mechanical characteristic and crack propagation rates are influenced by crack length, but current research of environmentally assisted cracking (EAC) focuses on long crack and small crack is usually ignored. The mechanical characteristic nearby small crack tip for single-edge crack panel specimens during the EAC in high temperature water was studied, the specimens was made of nickel-base alloy and the finite element method was adopted. The results show that the stress and strain is much higher for small crack than that of long crack, and this lead to the higher crack propagation tendency of small crack. A corrected method is introduced to calculate the plastic zone size of small crack. The Irwin correction method can improve the accuracy of J integral of long crack, but errors still exists for small crack. So the numerical method with elastic plastic fracture method is recommended to calculated J integral for small crack under larger load condition considering the lack of mature theoretical guidance about the small crack. The crack propagation process of the EAC of structure materials serviced in nuclear power plants is suggested to divide into two small crack propagation and long crack propagation considering to the anomalous mechanical behavior of the small crack.
2016, 45(2):326-328.
Abstract:
Mn-doped ZnO nanocrystal was prepared on Si substrates by cathodic electrodeposition. X-ray diffraction (XRD) study suggested Mn ions substituted Zn position in ZnO crystal. Field-emission scanning electron microscopy (SEM) images showed the morphology of ZnO nanocrystal was column-like. In photoluminescence spectrum, the visible emission band was broadened because of the doping effect. The fitted result of the temperature-dependent PL spectra in the range from 122.8K to 302.2K showed that Mn dopant could result in the decrease of the exciton binding energy.
Mn-doped ZnO nanocrystal was prepared on Si substrates by cathodic electrodeposition. X-ray diffraction (XRD) study suggested Mn ions substituted Zn position in ZnO crystal. Field-emission scanning electron microscopy (SEM) images showed the morphology of ZnO nanocrystal was column-like. In photoluminescence spectrum, the visible emission band was broadened because of the doping effect. The fitted result of the temperature-dependent PL spectra in the range from 122.8K to 302.2K showed that Mn dopant could result in the decrease of the exciton binding energy.
2016, 45(2):329-332.
Abstract:
WCu composites were fabricated by infiltrating Cu alloys doped with Zr and Cr into W skeleton in order to strengthen the W/Cu interfaces. The effect of Zr and Cr on the mechanical behaviours including flexural strength and impact toughness, and thermal shock resistance of WCu composites was investigated. The results show that the addition of a small amount of Zr and Cr increase the flexural strength and impact toughness of WCu composites. With the increase of thermal shock temperature, the flexural strength of WCu composites decreases. However, the addition of Zr and Cr in WCu composite can reduce the effect of thermal shock on mechanical behaviours obviously.
WCu composites were fabricated by infiltrating Cu alloys doped with Zr and Cr into W skeleton in order to strengthen the W/Cu interfaces. The effect of Zr and Cr on the mechanical behaviours including flexural strength and impact toughness, and thermal shock resistance of WCu composites was investigated. The results show that the addition of a small amount of Zr and Cr increase the flexural strength and impact toughness of WCu composites. With the increase of thermal shock temperature, the flexural strength of WCu composites decreases. However, the addition of Zr and Cr in WCu composite can reduce the effect of thermal shock on mechanical behaviours obviously.
2016, 45(2):333-338.
Abstract:
Effect of Si on the brazability and microstructure of Al-40Zn-xSi filler metal was studied, the microstructure and the mechanical properties of the joints which brazed with Al-40Zn-xSi filler metal were investigated respectively. The results indicate that the Al-40Zn-xSi filler metal presents the best wettability on 6061 aluminum alloy when Si content is at 4.0 wt. %. The microstructure of the filler metal indicates that the primary silicon particles could be found when the silicon content exceeds 4.0 wt. %. Al-Si eutectic, mixed with Zn-Al eutectoid, locate at α-Al interdendritic regions in the brazing seam after cooled with water. Moreover, the Al-40Zn-4Si joint possesses the optimum shear strength at 142.28 MPa. However, excess Si would increase the amount of brittle eutectic structures and primary silicon particles in the brazed joints, and thereby decrease the mechanical properties.
Effect of Si on the brazability and microstructure of Al-40Zn-xSi filler metal was studied, the microstructure and the mechanical properties of the joints which brazed with Al-40Zn-xSi filler metal were investigated respectively. The results indicate that the Al-40Zn-xSi filler metal presents the best wettability on 6061 aluminum alloy when Si content is at 4.0 wt. %. The microstructure of the filler metal indicates that the primary silicon particles could be found when the silicon content exceeds 4.0 wt. %. Al-Si eutectic, mixed with Zn-Al eutectoid, locate at α-Al interdendritic regions in the brazing seam after cooled with water. Moreover, the Al-40Zn-4Si joint possesses the optimum shear strength at 142.28 MPa. However, excess Si would increase the amount of brittle eutectic structures and primary silicon particles in the brazed joints, and thereby decrease the mechanical properties.
2016, 45(2):339-345.
Abstract:
Compression tests were done at temperature ranging from 250 to 450℃,strain-rate from 0.005 to 5 s-1 and the rolling tests were conducted. Combined with the modified peak strain model , peak stress model and quadratic equation and linear equation which were commonly used in mathematics, a new model of deformation resistance was established. Analyzing the rolling characteristics of magnesium plate, a geometric model in rolling deformation region was solved. Considering the factors of regional deformation spread and material characteristics, based on the principle of heat transfer and rolling theory, the rolling force model of different deformation areas and total rolling force model were established. The results showed that: The Sellars peak strain model after simplified of high precision was relatively simple in the form. The solution of peak stress model in reasonable temperature range improved the predicted accuracy effectively. The new model of resistance to deformation, not only had a easy form to apply to the actual production, but could accurately predict the deformation mechanism of a wide range of deformation under the conditions. Width elongation factors can not be ignored in rolling deformation zone and edge cracks and other defects were mainly produced in the backward slide area, so rolling force models should be established in the backward slide area and the forward slide area. Under different rolling conditions, the results of the model solution were consistent with the rolling tests of hot rolling process.
Compression tests were done at temperature ranging from 250 to 450℃,strain-rate from 0.005 to 5 s-1 and the rolling tests were conducted. Combined with the modified peak strain model , peak stress model and quadratic equation and linear equation which were commonly used in mathematics, a new model of deformation resistance was established. Analyzing the rolling characteristics of magnesium plate, a geometric model in rolling deformation region was solved. Considering the factors of regional deformation spread and material characteristics, based on the principle of heat transfer and rolling theory, the rolling force model of different deformation areas and total rolling force model were established. The results showed that: The Sellars peak strain model after simplified of high precision was relatively simple in the form. The solution of peak stress model in reasonable temperature range improved the predicted accuracy effectively. The new model of resistance to deformation, not only had a easy form to apply to the actual production, but could accurately predict the deformation mechanism of a wide range of deformation under the conditions. Width elongation factors can not be ignored in rolling deformation zone and edge cracks and other defects were mainly produced in the backward slide area, so rolling force models should be established in the backward slide area and the forward slide area. Under different rolling conditions, the results of the model solution were consistent with the rolling tests of hot rolling process.
2016, 45(2):346-352.
Abstract:
The tensile stress-strain curves and creep curves of commercial pure titanium TA2 at service temperature range (room temperature, 353K, 423K) were observed by tensile testing and creep testing. Based on the creep testing results, the significant creep phenomenon was observed at the service temperature range, and the creep feature was changing with temperature. Then, the tensile constitutive equation and the creep constitutive equation were constructed for TA2. Combining the tensile and the creep constitutive equations, the isochronous stress-strain curves were generated. The isochronous stress-strain curves of TA2 were much lower than the tensile stress-strain curves, and the isochronous stress-strain curves are decreasing with design life. Moreover, the variation feature of isochronous stress-strain curves with design life is changing with temperature. Based on the isochronous stress-strain curves, allowable limit strain and design life, the time dependent allowable stress of CP-Ti was proposed.
The tensile stress-strain curves and creep curves of commercial pure titanium TA2 at service temperature range (room temperature, 353K, 423K) were observed by tensile testing and creep testing. Based on the creep testing results, the significant creep phenomenon was observed at the service temperature range, and the creep feature was changing with temperature. Then, the tensile constitutive equation and the creep constitutive equation were constructed for TA2. Combining the tensile and the creep constitutive equations, the isochronous stress-strain curves were generated. The isochronous stress-strain curves of TA2 were much lower than the tensile stress-strain curves, and the isochronous stress-strain curves are decreasing with design life. Moreover, the variation feature of isochronous stress-strain curves with design life is changing with temperature. Based on the isochronous stress-strain curves, allowable limit strain and design life, the time dependent allowable stress of CP-Ti was proposed.
2016, 45(2):353-357.
Abstract:
This paper is the use of X-ray diffraction (XRD) techniques and electron backscatter diffraction (EBSD) technique to research the variation of polycrystalline pure cobalt tissue which is annealed at different temperatures. The results showed that:∑3 twin boundaries were observed in the retained FCC phase and we also find the number of grains having such a characteristic is not changed with annealing temperature, basically stable. Meanwhile, having a hexagonal close-packed (HCP) structure formed large grains of 71.4°/<11﹣20> special boundaries during the annealing process. Through analysis showed that the reasons and causes the formation of 71.4°/<11﹣20> special boundaries are not the same as the ∑3 twin boundaries which were formed in the retained FCC phase; 71.4°/<11﹣20> is formed as a result of phase transformation from FCC to HCP, following the Shoji-Nishiyama orientation relationship.
This paper is the use of X-ray diffraction (XRD) techniques and electron backscatter diffraction (EBSD) technique to research the variation of polycrystalline pure cobalt tissue which is annealed at different temperatures. The results showed that:∑3 twin boundaries were observed in the retained FCC phase and we also find the number of grains having such a characteristic is not changed with annealing temperature, basically stable. Meanwhile, having a hexagonal close-packed (HCP) structure formed large grains of 71.4°/<11﹣20> special boundaries during the annealing process. Through analysis showed that the reasons and causes the formation of 71.4°/<11﹣20> special boundaries are not the same as the ∑3 twin boundaries which were formed in the retained FCC phase; 71.4°/<11﹣20> is formed as a result of phase transformation from FCC to HCP, following the Shoji-Nishiyama orientation relationship.
2016, 45(2):358-362.
Abstract:
Fe40Co40Zr(10-x)MoxB9Cu1(x=0,2,4) amorphous alloys were prepared by the single roller melt-spinning and isothermally annealed at different temperatures. Microstructures, thermal properties and magnetic properties of the samples were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA) and vibrating sample magnetometer (VSM). The results show that the apparent activation energies of Fe40Co40Zr(10-x)MoxB9Cu1(x=0,2,4) alloys decreases with the increase of the Mo content. Mo addition reduces the thermal property of the alloys. The increase of Mo content inhibits the precipitation of ZrCo3B2 compounds and refines the grain size of the alloys. Coercivity (Hc) of Fe40Co40MoxZr(10-x)B9Cu1(x=0,2,4) alloys increases with the increasing of annealing temperature gradually. Mo addition reduces the Hc obviously.
Fe40Co40Zr(10-x)MoxB9Cu1(x=0,2,4) amorphous alloys were prepared by the single roller melt-spinning and isothermally annealed at different temperatures. Microstructures, thermal properties and magnetic properties of the samples were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA) and vibrating sample magnetometer (VSM). The results show that the apparent activation energies of Fe40Co40Zr(10-x)MoxB9Cu1(x=0,2,4) alloys decreases with the increase of the Mo content. Mo addition reduces the thermal property of the alloys. The increase of Mo content inhibits the precipitation of ZrCo3B2 compounds and refines the grain size of the alloys. Coercivity (Hc) of Fe40Co40MoxZr(10-x)B9Cu1(x=0,2,4) alloys increases with the increasing of annealing temperature gradually. Mo addition reduces the Hc obviously.
2016, 45(2):363-368.
Abstract:
Abstract: The hot deformation behavior was investigated at the temperature of 1080~1180℃ and strain rate of 0.01~10 S-1 for GH4720Li alloy, by using the hot compression tests. True stress-true strain curves and deformation microstructures were investigated. Constitutive equation and processing map for hot working were established. The results show that dynamic recrystallization is the dominant softening mechanism during hot deformation. Fully recrystallized grain is obtained at strain of 0.7, temperature of 1120~1180℃ and strain rate of 0.1~1 S-1. The optimum hot deformation temperature is 1120~1140℃. The behavior of γ′ phrase precipitation is the reason for the prominent change of the peak value of stress and the hot deformation activation energy. The hot deformation activation energy value 602KJ/mol is the minimum at the temperature of 1160℃. When the strain rate is greater than 1 S-1, the alloy will occur to the flow instability.
Abstract: The hot deformation behavior was investigated at the temperature of 1080~1180℃ and strain rate of 0.01~10 S-1 for GH4720Li alloy, by using the hot compression tests. True stress-true strain curves and deformation microstructures were investigated. Constitutive equation and processing map for hot working were established. The results show that dynamic recrystallization is the dominant softening mechanism during hot deformation. Fully recrystallized grain is obtained at strain of 0.7, temperature of 1120~1180℃ and strain rate of 0.1~1 S-1. The optimum hot deformation temperature is 1120~1140℃. The behavior of γ′ phrase precipitation is the reason for the prominent change of the peak value of stress and the hot deformation activation energy. The hot deformation activation energy value 602KJ/mol is the minimum at the temperature of 1160℃. When the strain rate is greater than 1 S-1, the alloy will occur to the flow instability.
2016, 45(2):369-374.
Abstract:
Atmospheric corrosion behaviour of cast and as-extruded AM60 Mg alloy was studied in this paper. The results showed that the corrosion rate of cast alloy was higher than that of as-extruded alloy. α-Mg-Mg17Al12 eutectics in cast alloy had better corrosion resistance than α-Mg phase in outdoor atmospheric environment, which would lead to the α-Mg phase being corroded seriously than the nearby eutectics. Then, the corrosion films on as-extruded alloy would not be uniform and had a poor protective effect. The maxium depth of corrosion pit in as-extruded alloy was deeper than that in cast alloy. The as-extruded alloy had much uniform mircrostructures and did not contain eutectics than cast alloy, which caused the corrosion film formed on surface of the former had better protection effect than that on the latter’s surface. Extruded process can not lead to a decrease in atmospheric corrosion resistance of AM60 Mg alloy.
Atmospheric corrosion behaviour of cast and as-extruded AM60 Mg alloy was studied in this paper. The results showed that the corrosion rate of cast alloy was higher than that of as-extruded alloy. α-Mg-Mg17Al12 eutectics in cast alloy had better corrosion resistance than α-Mg phase in outdoor atmospheric environment, which would lead to the α-Mg phase being corroded seriously than the nearby eutectics. Then, the corrosion films on as-extruded alloy would not be uniform and had a poor protective effect. The maxium depth of corrosion pit in as-extruded alloy was deeper than that in cast alloy. The as-extruded alloy had much uniform mircrostructures and did not contain eutectics than cast alloy, which caused the corrosion film formed on surface of the former had better protection effect than that on the latter’s surface. Extruded process can not lead to a decrease in atmospheric corrosion resistance of AM60 Mg alloy.
2016, 45(2):375-380.
Abstract:
Ni-W-Si intermetallic composite coatings with W5Si3 compound phase as the reinforcing phase were fabricated on AISI 304 stainless steel by laser alloying process using Ni-W-Si powers. The microstructure and composition of the coatings was characterized by SEM, XRD and EDS. The effect of the W、Si content on the hardness and wear resistance of coatings was investigated. Results indicate that a great deal of petaloid or cellular compound phase of W5Si3、CrSi2 and (Fe, Ni) solid solution were found after laser alloying process. Unmelted W particles were found particularly in the coatings with high proportion of tungsten. New alloy phase nucleated and grown into petaloid structure around W. The wear mechanism was mainly abrasive wear. Attributed to the high hardness and toughness of W5Si3, coatings had high hardness (the highest being 1040HV) and the wear resistance was elevated to 4~8 times higher.
Ni-W-Si intermetallic composite coatings with W5Si3 compound phase as the reinforcing phase were fabricated on AISI 304 stainless steel by laser alloying process using Ni-W-Si powers. The microstructure and composition of the coatings was characterized by SEM, XRD and EDS. The effect of the W、Si content on the hardness and wear resistance of coatings was investigated. Results indicate that a great deal of petaloid or cellular compound phase of W5Si3、CrSi2 and (Fe, Ni) solid solution were found after laser alloying process. Unmelted W particles were found particularly in the coatings with high proportion of tungsten. New alloy phase nucleated and grown into petaloid structure around W. The wear mechanism was mainly abrasive wear. Attributed to the high hardness and toughness of W5Si3, coatings had high hardness (the highest being 1040HV) and the wear resistance was elevated to 4~8 times higher.
2016, 45(2):381-386.
Abstract:
The flow stress curve of Nickel base Alloy Hastelloy C-276 during hot deformation was investigated by compression test under varying temperature and strain rates up to a true strain of 0.7 on Gleeble 3500 simulator. Dynamic recrystallization(DRX) occurred during hot deformation. The recrystallization critical conditions were determined by relationships between work hardening rate and stress curve. Adopt Johnson-Mehl-Avrami(JMA) equation to calculate recrystallization volume fraction experimental value, established the dynamic recrystallization volume fraction model and grain growth forecast model of Hastelloy C-276 alloy. The results show that the increasement of recrystallization volume fraction presents the typical "S" type curve with the increase of strain. The equation of critical strain conditions was established ．The equation of recrystallization volume fraction is ，and the average error of the predicted values and experimental values was 2.16%. The grain growth equation is , the average error was 6.63%.
The flow stress curve of Nickel base Alloy Hastelloy C-276 during hot deformation was investigated by compression test under varying temperature and strain rates up to a true strain of 0.7 on Gleeble 3500 simulator. Dynamic recrystallization(DRX) occurred during hot deformation. The recrystallization critical conditions were determined by relationships between work hardening rate and stress curve. Adopt Johnson-Mehl-Avrami(JMA) equation to calculate recrystallization volume fraction experimental value, established the dynamic recrystallization volume fraction model and grain growth forecast model of Hastelloy C-276 alloy. The results show that the increasement of recrystallization volume fraction presents the typical "S" type curve with the increase of strain. The equation of critical strain conditions was established ．The equation of recrystallization volume fraction is ，and the average error of the predicted values and experimental values was 2.16%. The grain growth equation is , the average error was 6.63%.
2016, 45(2):387-392.
Abstract:
Nb-Si based ultrahigh temperature alloys were prepared by vacuum non-consumable arc melting and the effects of Ti addition contents on their microstructure and phase composition were investigated. The results showed that Ti addition contents could exert an obvious influence on the types, sizes and area fractions of primary (Nb,X)5Si3 in the microstructure. When Ti addition content was relatively low (0-10 at.%), the primary silicides were α-(Nb,X)5Si3 and its area fraction increased significantly with increase in Ti addition content. When the Ti addition content was ranged from 18-20 at.%, the primary silicides were of two types: respectively α-(Nb,X)5Si3 and γ-(Nb,X)5Si3. However, the amount of α-(Nb,X)5Si3 decreased with increase in the Ti addition content in the alloy. When Ti addition content in the alloy varied from 22-30 at.%, there was only one form of primary silicides i.e., γ-(Nb,X)5Si3 left. Moreover, as the Ti addition content in the alloy increased, the size of α-(Nb,X)5Si3 increased while the size of γ-(Nb,X)5Si3 was less affected. In addition, as the Ti addition content in the alloy increased, Ti concentration in both Nbss and γ-(Nb,X)5Si3 increased while that in α-(Nb,X)5Si3 was lower and did not change obviously. It should also be noticed that Ti atoms only replaced Nb atoms in various phases while had no obvious effects on the solution tendency of other alloying elements such as Al, Cr and Hf.
Nb-Si based ultrahigh temperature alloys were prepared by vacuum non-consumable arc melting and the effects of Ti addition contents on their microstructure and phase composition were investigated. The results showed that Ti addition contents could exert an obvious influence on the types, sizes and area fractions of primary (Nb,X)5Si3 in the microstructure. When Ti addition content was relatively low (0-10 at.%), the primary silicides were α-(Nb,X)5Si3 and its area fraction increased significantly with increase in Ti addition content. When the Ti addition content was ranged from 18-20 at.%, the primary silicides were of two types: respectively α-(Nb,X)5Si3 and γ-(Nb,X)5Si3. However, the amount of α-(Nb,X)5Si3 decreased with increase in the Ti addition content in the alloy. When Ti addition content in the alloy varied from 22-30 at.%, there was only one form of primary silicides i.e., γ-(Nb,X)5Si3 left. Moreover, as the Ti addition content in the alloy increased, the size of α-(Nb,X)5Si3 increased while the size of γ-(Nb,X)5Si3 was less affected. In addition, as the Ti addition content in the alloy increased, Ti concentration in both Nbss and γ-(Nb,X)5Si3 increased while that in α-(Nb,X)5Si3 was lower and did not change obviously. It should also be noticed that Ti atoms only replaced Nb atoms in various phases while had no obvious effects on the solution tendency of other alloying elements such as Al, Cr and Hf.
2016, 45(2):393-398.
Abstract:
In order to study the deformation resistance problem of a pure titanium coil of the finishing rolling section of hot continuous rolling process, according to the actual rolling process of industrial production, a hot compression test on pure titanium was carried out in the following conditions: the deformation temperature range was 700~800℃, the strain rate was 5~25s-1, the maximum deformation was 0.8. The results show that the flow stress of pure titanium decreases with the increase of deformation temperature, while increases with the increase of strain rate. The effect of temperature and strain rateon thedeformation mechanism was higher. The deformation was mainly dynamic recovery when the temperature was 700℃and the strain rate was 1s-1. The degree of dynamic recrystallizationincreased continuouslywith the increase of temperature and strain rate. the dynamic recrystallizationwas the most complete at the temperature of 800 ℃and the strain rate of 20s-1, whose microstructure wasthe most homogeneous. According to the true stress-strain data obtained from thermal simulation experiment, as well as considering the influence of chemical composition, and based on the deformation resistance model of Johnson-Cook model, a deformation resistance model was developed, which can reflect many factors. Comparing the calculated value of rolling force based on the deformation resistance model with the actual value verified the reliability of the model. The model provides an effective basis for finishing rolling technical control of pure titanium coil in the hot continuous rolling process.
In order to study the deformation resistance problem of a pure titanium coil of the finishing rolling section of hot continuous rolling process, according to the actual rolling process of industrial production, a hot compression test on pure titanium was carried out in the following conditions: the deformation temperature range was 700~800℃, the strain rate was 5~25s-1, the maximum deformation was 0.8. The results show that the flow stress of pure titanium decreases with the increase of deformation temperature, while increases with the increase of strain rate. The effect of temperature and strain rateon thedeformation mechanism was higher. The deformation was mainly dynamic recovery when the temperature was 700℃and the strain rate was 1s-1. The degree of dynamic recrystallizationincreased continuouslywith the increase of temperature and strain rate. the dynamic recrystallizationwas the most complete at the temperature of 800 ℃and the strain rate of 20s-1, whose microstructure wasthe most homogeneous. According to the true stress-strain data obtained from thermal simulation experiment, as well as considering the influence of chemical composition, and based on the deformation resistance model of Johnson-Cook model, a deformation resistance model was developed, which can reflect many factors. Comparing the calculated value of rolling force based on the deformation resistance model with the actual value verified the reliability of the model. The model provides an effective basis for finishing rolling technical control of pure titanium coil in the hot continuous rolling process.
2016, 45(2):399-403.
Abstract:
The ductile fracture of metal materials, which is the most common failure mode and important factor for hot workability in plastic forming, is always the research focus in the field of advanced plastic processing. A new fracture criterion is thus necessary to accurately predict the hot deformation fracture for the optimization of processes and improvement of products. In present study, a novel high-speed photography is introduced to determine the critical fracture strain of Ti60 high-temperature titanium alloy during hot compression deformation. This method can precisely captures the nucleation site and propagation process of cracking by two high-speed cameras fixed on opposite sides of the specimens, and thus is an efficient method to determination of the critical fracture strain in hot deformation processes. Based on Oh criterion, a new hot deformation fracture criterion considering strain rate and temperature effects is built and can be modeled as the function of Zener-Holloman parameter. By combining the DEFORM-3D simulation software and FROTRAN language, fracture initiation in the upsetting of large size Ti60 ingot can be precisely predicted which shows that the proposed prediction model is effective and practicable.
The ductile fracture of metal materials, which is the most common failure mode and important factor for hot workability in plastic forming, is always the research focus in the field of advanced plastic processing. A new fracture criterion is thus necessary to accurately predict the hot deformation fracture for the optimization of processes and improvement of products. In present study, a novel high-speed photography is introduced to determine the critical fracture strain of Ti60 high-temperature titanium alloy during hot compression deformation. This method can precisely captures the nucleation site and propagation process of cracking by two high-speed cameras fixed on opposite sides of the specimens, and thus is an efficient method to determination of the critical fracture strain in hot deformation processes. Based on Oh criterion, a new hot deformation fracture criterion considering strain rate and temperature effects is built and can be modeled as the function of Zener-Holloman parameter. By combining the DEFORM-3D simulation software and FROTRAN language, fracture initiation in the upsetting of large size Ti60 ingot can be precisely predicted which shows that the proposed prediction model is effective and practicable.
2016, 45(2):404-408.
Abstract:
This paper deals with the evolution law of microstructure and formation process of intracrystalline liquid pool of extruded AZ80 magnesium alloy after being treated through semi-solid isothermal treatment (SST) for different time. The result show that, with the semi-solid isothermal process, merger of grain coarsening occurs firstly, and then liquid phase appeares and expansion; with the increase of isothermal holding time, the α-Mg grains separated by liquid phase and tend to spheroid constantly, Ostwald ripening and grain coalescing will become the main mechanism with continue increase holding time. And the liquid pool inside the α-Mg grain is caused with the main mechanism of intracrystalline partial melting priority due to elements enrichment. And the partial zone with low melting cased with the solution elements enrichment melting priority is the main mechanism of intracrystalline liquid pool inside the α-Mg grain.
This paper deals with the evolution law of microstructure and formation process of intracrystalline liquid pool of extruded AZ80 magnesium alloy after being treated through semi-solid isothermal treatment (SST) for different time. The result show that, with the semi-solid isothermal process, merger of grain coarsening occurs firstly, and then liquid phase appeares and expansion; with the increase of isothermal holding time, the α-Mg grains separated by liquid phase and tend to spheroid constantly, Ostwald ripening and grain coalescing will become the main mechanism with continue increase holding time. And the liquid pool inside the α-Mg grain is caused with the main mechanism of intracrystalline partial melting priority due to elements enrichment. And the partial zone with low melting cased with the solution elements enrichment melting priority is the main mechanism of intracrystalline liquid pool inside the α-Mg grain.
28 Ultra-coarse Grain WC-Co Cemented Carbide from Chemical Coated Powder by One-step Hydrogen Reduction
2016, 45(2):409-414.
Abstract:
The ultra-coarse grain WC-8w%Co cemented carbide with an average grain size of 8.9μm was prepared from WC-Co chemical coated powders produced by merging the preparation of Co powder with the mixing of WC and Co. The tungsten carbide powder with Fiss particle size of 4.1μm, cobalt chloride and ammonium oxalate were used as the raw materials. Microstructures，phase constitutes and properties of composite powders as well as cemented carbides were characterized by Scanning electron microscopy (SEM), Chemical element analysis, X-ray diffractometry (XRD) and so on．The results shows that, in the WC-Co chemical coated powders, cobalt exists in fcc and hcp structure and exhibits the irregular shapes on the surface of WC particles. The cemented carbide prepared from carbide WC-Co chemical coated powders has a homogeneous microstructure and excellent mechanical properties while density, hardness, transverse rupture strength and fracture toughness is 14.63g?cm-3，87.6HRA, 2438MPa and 20.92 MPa?m1/2,respectively.The chemical coated method does not only overcome the defect of wet mixing reducing WC grain size remarkably, but also has advantage of low cost and simple technological process.
The ultra-coarse grain WC-8w%Co cemented carbide with an average grain size of 8.9μm was prepared from WC-Co chemical coated powders produced by merging the preparation of Co powder with the mixing of WC and Co. The tungsten carbide powder with Fiss particle size of 4.1μm, cobalt chloride and ammonium oxalate were used as the raw materials. Microstructures，phase constitutes and properties of composite powders as well as cemented carbides were characterized by Scanning electron microscopy (SEM), Chemical element analysis, X-ray diffractometry (XRD) and so on．The results shows that, in the WC-Co chemical coated powders, cobalt exists in fcc and hcp structure and exhibits the irregular shapes on the surface of WC particles. The cemented carbide prepared from carbide WC-Co chemical coated powders has a homogeneous microstructure and excellent mechanical properties while density, hardness, transverse rupture strength and fracture toughness is 14.63g?cm-3，87.6HRA, 2438MPa and 20.92 MPa?m1/2,respectively.The chemical coated method does not only overcome the defect of wet mixing reducing WC grain size remarkably, but also has advantage of low cost and simple technological process.
2016, 45(2):415-420.
Abstract:
Al-Mg alloy plates with 10mm thick were welded by multipass MIG welding with the self-made wire as filler material, and microstructure of the welded joint were examined by metallographic, scanning electron microscope (SEM), X-ray diffraction and electron backscatter diffraction (EBSD). The results show that weld zone is typical of casting microstructure, and no obvious preferred orientation. Comparatively, grains are more inclined to epitaxial growth, and the texture in reheating coarse grain heat-affected zone is more obvious than fine grain layer and weld zone because of the comprehensive additive effect of welding thermal cycle and the structural similarity on the interface during multipass welding, grain growth is more apparent, microhardness is more low, and the residual stress value is only second to weld bottom, which is the weakest link.
Al-Mg alloy plates with 10mm thick were welded by multipass MIG welding with the self-made wire as filler material, and microstructure of the welded joint were examined by metallographic, scanning electron microscope (SEM), X-ray diffraction and electron backscatter diffraction (EBSD). The results show that weld zone is typical of casting microstructure, and no obvious preferred orientation. Comparatively, grains are more inclined to epitaxial growth, and the texture in reheating coarse grain heat-affected zone is more obvious than fine grain layer and weld zone because of the comprehensive additive effect of welding thermal cycle and the structural similarity on the interface during multipass welding, grain growth is more apparent, microhardness is more low, and the residual stress value is only second to weld bottom, which is the weakest link.
2016, 45(2):421-425.
Abstract:
Ag-Cu-Ge eutectic solder ribbons were prepared by single roller rapid solidification. Melting temperature and phase composition of solder alloys were determined by DSC and XRD. The microstructure and morphology of solder alloys and brazing joints were observed by scanning electron microscope (SEM), and the chemical composition was analyzed by energy dispersive spectrometer (EDS). The results show that the liquidus temperature of rapidly solidified Ag-Cu-Ge solder decreases 4.8℃ and its melting temperature range reduces 4.4℃. The microstructure of cast solder is massive and heavy segregation, while rapidly solidified solder has finer microstructures and higher composition homogeneity; Rapidly solidified Ag-Cu-Ge solder has a better wettability and spreadability, wider transition layer thickness and higher shear strength of brazed joints with Cu and Ni substrate compared with the same constituent common solder. Congruent compounds which grows up as a layer is found on the interface of solder alloy with copper substrate, while incongruent compounds which grows up as bamboo shoot form is found on the interfaces of solder alloy and substrate. This embedded structure is helpful to improve the strength of brazed joints
Ag-Cu-Ge eutectic solder ribbons were prepared by single roller rapid solidification. Melting temperature and phase composition of solder alloys were determined by DSC and XRD. The microstructure and morphology of solder alloys and brazing joints were observed by scanning electron microscope (SEM), and the chemical composition was analyzed by energy dispersive spectrometer (EDS). The results show that the liquidus temperature of rapidly solidified Ag-Cu-Ge solder decreases 4.8℃ and its melting temperature range reduces 4.4℃. The microstructure of cast solder is massive and heavy segregation, while rapidly solidified solder has finer microstructures and higher composition homogeneity; Rapidly solidified Ag-Cu-Ge solder has a better wettability and spreadability, wider transition layer thickness and higher shear strength of brazed joints with Cu and Ni substrate compared with the same constituent common solder. Congruent compounds which grows up as a layer is found on the interface of solder alloy with copper substrate, while incongruent compounds which grows up as bamboo shoot form is found on the interfaces of solder alloy and substrate. This embedded structure is helpful to improve the strength of brazed joints
2016, 45(2):426-430.
Abstract:
The industrial nickel alloy N6 was experimentally studied by Plasma arc welding with filler wire and without filler wire process. The effects of welding on microstructure, hardness, electricity, corrosion resistance and electrical conductivity of nickel alloy N6 were investigated by microstructure observation、XRD analysis、hardness、corrosion weight loss and resistivity testing.The results showed that the effects of welding procedure on corrosion resistance and electrical conductivity.The corrosion resistance of the weld with filler wire and without filler wire deceased compared with the base metal. The corrosion rate and resistivity of welded joints without filler wire is larger than that welded joints with filler wire. The corrosion resistance of the base metal and welded metal is mainly dependent on microstructure, hardness and inclusions；The resistivity is associated with such factors as grain size and inclusions.
The industrial nickel alloy N6 was experimentally studied by Plasma arc welding with filler wire and without filler wire process. The effects of welding on microstructure, hardness, electricity, corrosion resistance and electrical conductivity of nickel alloy N6 were investigated by microstructure observation、XRD analysis、hardness、corrosion weight loss and resistivity testing.The results showed that the effects of welding procedure on corrosion resistance and electrical conductivity.The corrosion resistance of the weld with filler wire and without filler wire deceased compared with the base metal. The corrosion rate and resistivity of welded joints without filler wire is larger than that welded joints with filler wire. The corrosion resistance of the base metal and welded metal is mainly dependent on microstructure, hardness and inclusions；The resistivity is associated with such factors as grain size and inclusions.
2016, 45(2):431-435.
Abstract:
The microstructures of Mg-10Gd-3Y-1.2Zn-0.5Zr alloys after solution heat treatment at different temperatures comparing with the as-cast conditions were studied by using the optical microscope, XRD, SEM and TEM. The results showed that the LPSO lamellar phase grew with time increasing under the conditions of isothermal solution. At same time, the lamellar phase extending into grain which induced the lamellar to become widen. The original cast lamellar phase dissolution with the temperature increasing, however, a wider lamellar phase produced along compound located at the grain boundary. The new lamellar phase width increased with time. The alloy after solution treatment at 525℃ the sample hardness could reach 115 HV.
The microstructures of Mg-10Gd-3Y-1.2Zn-0.5Zr alloys after solution heat treatment at different temperatures comparing with the as-cast conditions were studied by using the optical microscope, XRD, SEM and TEM. The results showed that the LPSO lamellar phase grew with time increasing under the conditions of isothermal solution. At same time, the lamellar phase extending into grain which induced the lamellar to become widen. The original cast lamellar phase dissolution with the temperature increasing, however, a wider lamellar phase produced along compound located at the grain boundary. The new lamellar phase width increased with time. The alloy after solution treatment at 525℃ the sample hardness could reach 115 HV.
2016, 45(2):436-438.
Abstract:
The pure anatase phase nanometer TiO2 powder were prepared by sol–gel method using tetrabutyl titanate, absolute ethyl alcohol and glacial acetic acid as starting materials, and using anhydrous potassium pyrophosphate and sodium pyrophosphate as dispersants. TEM micrographs and XRD results show that the particle-size distribution range is between 25 and 40 nm. The pure anatase phase nanometer TiO2 powder exhibit good ultraviolet shielding properties in a wavelength range of 280~380nm and good permeability in the visible region, which can be used to prepare ultraviolet shielding materials in low cost and high performance.
The pure anatase phase nanometer TiO2 powder were prepared by sol–gel method using tetrabutyl titanate, absolute ethyl alcohol and glacial acetic acid as starting materials, and using anhydrous potassium pyrophosphate and sodium pyrophosphate as dispersants. TEM micrographs and XRD results show that the particle-size distribution range is between 25 and 40 nm. The pure anatase phase nanometer TiO2 powder exhibit good ultraviolet shielding properties in a wavelength range of 280~380nm and good permeability in the visible region, which can be used to prepare ultraviolet shielding materials in low cost and high performance.
2016, 45(2):439-444.
Abstract:
In the process of laser micro cladding deposition manufacturing of TC4, the influence of the laser power and scanning speed on the microstructure and micro-hardness were analyzed. The results indicate that the prior β columnar grains dominate the entire cladding layer or the columnar are epitaxial growth with a thin layer of fine dendritic microstructure in the top. There are two regions of bright region and dark region in the macrostructure. When P/V is less than 40 W?s?mm-1, the bright region is in the top and the dark region is below it. The microstructure of the two regions is acicular martensite and it is finer in bright region than in dark region. The micro-hardness of the bright region is higher than the dark region and at the same time, when the laser power increased or the scanning speed reduced, the height of the bright region increased and the micro-hardness of the bright and dark region all decreased. Otherwise, the bright region is under the dark region. In this case the microstructure of the bright region is still acicular martensite, and the microstructure of the dark region is coarsened from acicular martensite by a solution and aging treatment of the repeated heating，at the same time the micro-hardness of the dark region is higher than the bright region .
In the process of laser micro cladding deposition manufacturing of TC4, the influence of the laser power and scanning speed on the microstructure and micro-hardness were analyzed. The results indicate that the prior β columnar grains dominate the entire cladding layer or the columnar are epitaxial growth with a thin layer of fine dendritic microstructure in the top. There are two regions of bright region and dark region in the macrostructure. When P/V is less than 40 W?s?mm-1, the bright region is in the top and the dark region is below it. The microstructure of the two regions is acicular martensite and it is finer in bright region than in dark region. The micro-hardness of the bright region is higher than the dark region and at the same time, when the laser power increased or the scanning speed reduced, the height of the bright region increased and the micro-hardness of the bright and dark region all decreased. Otherwise, the bright region is under the dark region. In this case the microstructure of the bright region is still acicular martensite, and the microstructure of the dark region is coarsened from acicular martensite by a solution and aging treatment of the repeated heating，at the same time the micro-hardness of the dark region is higher than the bright region .
2016, 45(2):445-448.
Abstract:
Selecting appropriate wall material is the key to reduce the consumption of precursor in the hot wall chemical vapour deposition process that is used to prepare platinum films so that the partial press of precursor could be maintained. The ease of Pt fimls deposition was compared in this paper. The compared substrates were nickel-based superalloy, copper with oxide layer for the candidate of depositon chamber material and pure copper. The result shows that the copper with oxide layer is the hardest deposited in these experiments. Although the copper with oxide layer could be used as the substrate material in hot wall CVD, it can be only used one time.
Selecting appropriate wall material is the key to reduce the consumption of precursor in the hot wall chemical vapour deposition process that is used to prepare platinum films so that the partial press of precursor could be maintained. The ease of Pt fimls deposition was compared in this paper. The compared substrates were nickel-based superalloy, copper with oxide layer for the candidate of depositon chamber material and pure copper. The result shows that the copper with oxide layer is the hardest deposited in these experiments. Although the copper with oxide layer could be used as the substrate material in hot wall CVD, it can be only used one time.
2016, 45(2):449-453.
Abstract:
Brittle intermetallic compounds in brazing joint of Titanium and steel easily make its weld organization and mechanical properties worsen. In order to solve this problem, we do a series of contrast test that the Ni layer is plated on matching surface of base metal or not. On this basis, the influencing mechanism of atomic diffusion behavior, microstructure and mechanical properties of the brazing joint were researched. The test results show that, the Ni layer blocks the atoms diffusion of brazing joint. Moreover, the degree of obstruction are differences among Fe,Ti and other atoms. Further, this differential is in close relationship with physical location of Ni layer in the joint region. The hinder of Ni layer alters osmotic concentration of the atoms, slows the metallurgical reaction degree, and reduces the content of brittle intermetallic compounds .Consequently, the microstructure and mechanical properties of brazing joint can be effectively improved because of the existence of Ni layer.
Brittle intermetallic compounds in brazing joint of Titanium and steel easily make its weld organization and mechanical properties worsen. In order to solve this problem, we do a series of contrast test that the Ni layer is plated on matching surface of base metal or not. On this basis, the influencing mechanism of atomic diffusion behavior, microstructure and mechanical properties of the brazing joint were researched. The test results show that, the Ni layer blocks the atoms diffusion of brazing joint. Moreover, the degree of obstruction are differences among Fe,Ti and other atoms. Further, this differential is in close relationship with physical location of Ni layer in the joint region. The hinder of Ni layer alters osmotic concentration of the atoms, slows the metallurgical reaction degree, and reduces the content of brittle intermetallic compounds .Consequently, the microstructure and mechanical properties of brazing joint can be effectively improved because of the existence of Ni layer.
2016, 45(2):454-458.
Abstract:
A ultra-fine grain 9Cr-oxide dispersion strengthened (ODS) steel was prepared by spark plasma sintering (SPS) method, instead of the traditional hot isostatic pressing (HIP). The microstructure and density of SPS-ODS steels with different sintering temperatures (900癈，950癈，1050癈) were analyzed by SEM and Archimedes' Principle, respectively. The grain size and precipitates characterization of SPS-ODS steel were analyzed by HRTEM, STEM-HAADF and EDS. The results showed that 950癈 is the optimal SPS temperature and the relative density reaches up to 97.7%. The mixture of ultra-fine nano grains (≤200nm) and coarsen grains (≥1μm) is observed in SPS ODS steel; High-density nano-sized Y-Ti-O clusters and Y2Ti2O7 phases are dispersed homogenously in the ODS steel. Large size spinel structured Mn(Ti)Cr2O4 precipitates (30-100nm) are formed mainly at grain boundaries.
A ultra-fine grain 9Cr-oxide dispersion strengthened (ODS) steel was prepared by spark plasma sintering (SPS) method, instead of the traditional hot isostatic pressing (HIP). The microstructure and density of SPS-ODS steels with different sintering temperatures (900癈，950癈，1050癈) were analyzed by SEM and Archimedes' Principle, respectively. The grain size and precipitates characterization of SPS-ODS steel were analyzed by HRTEM, STEM-HAADF and EDS. The results showed that 950癈 is the optimal SPS temperature and the relative density reaches up to 97.7%. The mixture of ultra-fine nano grains (≤200nm) and coarsen grains (≥1μm) is observed in SPS ODS steel; High-density nano-sized Y-Ti-O clusters and Y2Ti2O7 phases are dispersed homogenously in the ODS steel. Large size spinel structured Mn(Ti)Cr2O4 precipitates (30-100nm) are formed mainly at grain boundaries.
2016, 45(2):459-464.
Abstract:
Amorphous-Nanocrystalline powders of Ni79.3W20.7 and Ni55.1W17.9B27 were prepared by mechanically alloyed method. The microstructure characteristics and structure parameters of powders for different milling times were studied by SEM and XRD, respectively, and the effect of B additive on the progress of amorphization was analyzed. The research results showed that, during MA, the Ni79.3W20.7 was not amorphized, while the Ni55.1W17.9B27 was amorphized after 80 hours. It suggested that the addition of B improved the glass-forming ability of the Ni-W alloy systems. The amorphization progress was that W/B first dissolved in Ni to form Ni(W, B) supersaturated solid solution during MA, and then amorphization of Ni(W, B) supersaturated solid solution occurred. Furthermore, grain size and internal strain of Ni in Ni79.3W20.7 powder were 32.9nm and 0.48 pct after 30 hours of milling, whereas those of Ni55.1W17.9B27 powder were 9nm and 0.62 pct after 10 hours of milling.
Amorphous-Nanocrystalline powders of Ni79.3W20.7 and Ni55.1W17.9B27 were prepared by mechanically alloyed method. The microstructure characteristics and structure parameters of powders for different milling times were studied by SEM and XRD, respectively, and the effect of B additive on the progress of amorphization was analyzed. The research results showed that, during MA, the Ni79.3W20.7 was not amorphized, while the Ni55.1W17.9B27 was amorphized after 80 hours. It suggested that the addition of B improved the glass-forming ability of the Ni-W alloy systems. The amorphization progress was that W/B first dissolved in Ni to form Ni(W, B) supersaturated solid solution during MA, and then amorphization of Ni(W, B) supersaturated solid solution occurred. Furthermore, grain size and internal strain of Ni in Ni79.3W20.7 powder were 32.9nm and 0.48 pct after 30 hours of milling, whereas those of Ni55.1W17.9B27 powder were 9nm and 0.62 pct after 10 hours of milling.
2016, 45(2):465-469.
Abstract:
The effect of pre-deformation artificial aging on mocrostructure and properties of a novel aluminum-lithium alloy was investigated to achieve the superior combinations of strength and toughness. The mechanical properties were evaluated by tensile and tear test, and the precipitation behabiour was primarily characterized by TEM. The results indicated that the samples after a pre-deformation artificial aging possessed a preferable strength and toughness, owing to the precipitation of well-dispersed T1 (Al2CuLi) phases promoted by the plastic deformation. The formation and coarsening of PFZ were also effectively avoided in thie condition. The better combination of strength and toughness was obtained with the route of 4.5% pre-deformation 145℃, 35h aging.
The effect of pre-deformation artificial aging on mocrostructure and properties of a novel aluminum-lithium alloy was investigated to achieve the superior combinations of strength and toughness. The mechanical properties were evaluated by tensile and tear test, and the precipitation behabiour was primarily characterized by TEM. The results indicated that the samples after a pre-deformation artificial aging possessed a preferable strength and toughness, owing to the precipitation of well-dispersed T1 (Al2CuLi) phases promoted by the plastic deformation. The formation and coarsening of PFZ were also effectively avoided in thie condition. The better combination of strength and toughness was obtained with the route of 4.5% pre-deformation 145℃, 35h aging.
2016, 45(2):470-476.
Abstract:
Near-Equiatomic TiNi alloys were successfully produced by powder metallurgy (P/M) method using Ti and Ni powders in different temperatures(950℃，1000℃，1050℃，1100℃).To obtain a material surface having excellent affinity to bone, hydroxyapatite coatings were conducted in a simulated body fluid (SBF). Phase composition and surface structure of Ca-P coatings were characterized by X-ray diffractometry (XRD), Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDS) attached to SEM. Results indicated that porosity of TiNi alloys produced by P/M method is high and peaks of hydroxyapatite is sharp. In the same experimental condition, more apatite coatings formed on TiNi samples sintered at 1050℃ and 1100℃ due to their high porosity and pure TiNi phase that is beneficial to heterogeneous nucleation.
Near-Equiatomic TiNi alloys were successfully produced by powder metallurgy (P/M) method using Ti and Ni powders in different temperatures(950℃，1000℃，1050℃，1100℃).To obtain a material surface having excellent affinity to bone, hydroxyapatite coatings were conducted in a simulated body fluid (SBF). Phase composition and surface structure of Ca-P coatings were characterized by X-ray diffractometry (XRD), Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDS) attached to SEM. Results indicated that porosity of TiNi alloys produced by P/M method is high and peaks of hydroxyapatite is sharp. In the same experimental condition, more apatite coatings formed on TiNi samples sintered at 1050℃ and 1100℃ due to their high porosity and pure TiNi phase that is beneficial to heterogeneous nucleation.
2016, 45(2):477-481.
Abstract:
VC was added to the raw oxide materials which were synthesized to the nanocrystalline WC-Co composite powder by the in-situ reduction and carbonization process. The nanocrystalline WC-Co alloys were fabricated by the spark plasma sintering technique using the prepared WC-Co composite powder. The phase constitution microstructure characteristics and mechanical properties of the sintered cemented carbides were analyzed. The study proposed that VC plays a significant role in decrease the grain size of the prepared WC-Co alloy. The nanocrystalline WC-Co alloy with high hardness and good fracture toughness properties can be obtained as the amount of VC addition is appropriate.
VC was added to the raw oxide materials which were synthesized to the nanocrystalline WC-Co composite powder by the in-situ reduction and carbonization process. The nanocrystalline WC-Co alloys were fabricated by the spark plasma sintering technique using the prepared WC-Co composite powder. The phase constitution microstructure characteristics and mechanical properties of the sintered cemented carbides were analyzed. The study proposed that VC plays a significant role in decrease the grain size of the prepared WC-Co alloy. The nanocrystalline WC-Co alloy with high hardness and good fracture toughness properties can be obtained as the amount of VC addition is appropriate.
2016, 45(2):482-486.
Abstract:
Basic magnesium chloride whiskers were prepared with saltworks brine and Sodium Hydroxide as starting raw. Morphology and crystal Structure of products were investigated by SEM and SAED. The whiskers were single crystal material with the average Diameter of 0.5-1μm and length of more than 150μm. Crystalline structure of the samples were characterized by XRD, and product is 9Mg(OH)2?MgCl2?5H2O. It’s functional groups of different magnesium ion concentration were investigated by FT-IR. Magnesium oxide whiskers were program calcinated high temperature at heating rate of 2-5℃/min, Keeping the morphology and single crystal structure of magnesium oxide whiskers well. The possible mechanism of thermal decomposition process was speculated also.
Basic magnesium chloride whiskers were prepared with saltworks brine and Sodium Hydroxide as starting raw. Morphology and crystal Structure of products were investigated by SEM and SAED. The whiskers were single crystal material with the average Diameter of 0.5-1μm and length of more than 150μm. Crystalline structure of the samples were characterized by XRD, and product is 9Mg(OH)2?MgCl2?5H2O. It’s functional groups of different magnesium ion concentration were investigated by FT-IR. Magnesium oxide whiskers were program calcinated high temperature at heating rate of 2-5℃/min, Keeping the morphology and single crystal structure of magnesium oxide whiskers well. The possible mechanism of thermal decomposition process was speculated also.
Xing Qingyuan
,
Meng Linggang
,
Deng Liang
,
Yang Hongshuo
,
Zhen Liling
,
Liu Hongwei
,
Fan Canfeng
,
Fan Jianxun
,
Zhang Xingguo
2016, 45(2):487-492.
Abstract:
The effects of the different power, casting rate, quantity of cooling water and trace amount of Sc to 5356-Al alloy are investigated. The experiment shows 5356-Al alloy has the optimal surface and internal quality and tensile properties with the process parameters which the power is 10kw, the casting speed is 8-9cm/ min, the quantity of cooling water is 1.7m3/h. The tensile strength and elongation of 5356-Al alloy can be up to 310.0MPa and 16.3%, and the surface has no obvious casting defects. At the same time, the microstructure of the edge is equiaxed crystals basically, while the center is broken dendrite crystals with an uniform distribution of the second phases. Besides, the homogenization heat-treatment of 5356-Al alloy has also been established: 440℃?30h with the air cooling. After the homogenization heat-treatment, the micro-segregation of Mg has been eliminated basically and the phase Al8Mg5 which is distributing along the grain boundaries continuously dissolves significantly. In addition, trace amount of Sc can significantly improve the strength and plasticity of 5356-Al alloy. The experiment proves 5356-Al 0.4wt. %Sc alloy can refine the grain size and reduce the number of the second phase, the tensile strength and elongation can be up to 330.0MPa and 29.0%, which increased by 6.5% and 77.9% respectively.
The effects of the different power, casting rate, quantity of cooling water and trace amount of Sc to 5356-Al alloy are investigated. The experiment shows 5356-Al alloy has the optimal surface and internal quality and tensile properties with the process parameters which the power is 10kw, the casting speed is 8-9cm/ min, the quantity of cooling water is 1.7m3/h. The tensile strength and elongation of 5356-Al alloy can be up to 310.0MPa and 16.3%, and the surface has no obvious casting defects. At the same time, the microstructure of the edge is equiaxed crystals basically, while the center is broken dendrite crystals with an uniform distribution of the second phases. Besides, the homogenization heat-treatment of 5356-Al alloy has also been established: 440℃?30h with the air cooling. After the homogenization heat-treatment, the micro-segregation of Mg has been eliminated basically and the phase Al8Mg5 which is distributing along the grain boundaries continuously dissolves significantly. In addition, trace amount of Sc can significantly improve the strength and plasticity of 5356-Al alloy. The experiment proves 5356-Al 0.4wt. %Sc alloy can refine the grain size and reduce the number of the second phase, the tensile strength and elongation can be up to 330.0MPa and 29.0%, which increased by 6.5% and 77.9% respectively.
2016, 45(2):493-497.
Abstract:
The effect of isothermal heat treatment on the microstructure of semi-solid AZ91D Ce magnesium alloy was investigated and the ideal globular and near-globular microstructure was obtained. The results show that the rare earth Ce can hider aggregating and associating of the primary solid particles, inhibit growing of the solid particles and form fine well-distributed round semi-solid microstructure. During higher isothermal heat treatment temperature, there is more liquid phase due to the stronger movability of atoms and faster melting rate of solid particles. The size of solid particles is decreased first and then increased. The size of solid particles is mainly decided by melting in initial stage of isothermal heat treatment. Therefore, the size of solid particles is decreased. With further increasing of the isothermal heat treatment time, the size of solid particles is mainly decided by coarsening mechanism and Ostwald ripening and then the size of solid particles is increased.
The effect of isothermal heat treatment on the microstructure of semi-solid AZ91D Ce magnesium alloy was investigated and the ideal globular and near-globular microstructure was obtained. The results show that the rare earth Ce can hider aggregating and associating of the primary solid particles, inhibit growing of the solid particles and form fine well-distributed round semi-solid microstructure. During higher isothermal heat treatment temperature, there is more liquid phase due to the stronger movability of atoms and faster melting rate of solid particles. The size of solid particles is decreased first and then increased. The size of solid particles is mainly decided by melting in initial stage of isothermal heat treatment. Therefore, the size of solid particles is decreased. With further increasing of the isothermal heat treatment time, the size of solid particles is mainly decided by coarsening mechanism and Ostwald ripening and then the size of solid particles is increased.
45 Influence of modulation periods on microstructure and mechanical properties of Ti/TiB2 multilayers
2016, 45(2):498-502.
Abstract:
Ti/TiB2 multilayers with various modulation periods were prepared by magnetron sputtering system. An X-ray diffraction was used to characterize the phase and a scanning electron microscope was applied to observe the surface and fracture cross-sectional morphologies of multilayers. The mechanical properties of the multilayers such as nano-hardness, elastic modulus, adhesion and fracture toughness were evaluated with nanoindentation, universal micro materials tester and microhardness meter, respectively. The results show that the surface of multilayers is even, compact and smooth with clear nano-modulate structure and presents a good physical bonding between the coating and substrate. With the increase of the modulation periods of multilayers, the hardness and elastic modulus increases and attains the maximum value of 35.8 GPa and 349 GPa at the modulation period T=12. However, the fracture toughness of multilayers increases firstly and reaches maximum value (2.17 MPa?m1/2) at the modulation period T=6 and then decreases subsequently. Passivation effect occurs at the crack tip due to the insertion of Ti sub-layer in the multilayers, which leads to a path deflection of the crack propagation, as a result, improving the fracture toughness of the multilayers.
Ti/TiB2 multilayers with various modulation periods were prepared by magnetron sputtering system. An X-ray diffraction was used to characterize the phase and a scanning electron microscope was applied to observe the surface and fracture cross-sectional morphologies of multilayers. The mechanical properties of the multilayers such as nano-hardness, elastic modulus, adhesion and fracture toughness were evaluated with nanoindentation, universal micro materials tester and microhardness meter, respectively. The results show that the surface of multilayers is even, compact and smooth with clear nano-modulate structure and presents a good physical bonding between the coating and substrate. With the increase of the modulation periods of multilayers, the hardness and elastic modulus increases and attains the maximum value of 35.8 GPa and 349 GPa at the modulation period T=12. However, the fracture toughness of multilayers increases firstly and reaches maximum value (2.17 MPa?m1/2) at the modulation period T=6 and then decreases subsequently. Passivation effect occurs at the crack tip due to the insertion of Ti sub-layer in the multilayers, which leads to a path deflection of the crack propagation, as a result, improving the fracture toughness of the multilayers.
2016, 45(2):503-506.
Abstract:
The BCN thin films with TiN interlayer were deposited on HSS and silicon (100) substrates by an arc enhanced reactive magnetron sputtering (AEMS). Microstructure of the thin films was characterized by meanings of XRD and FTIR. Adhersion to the sustrate of the thin films were characterized by scrach test. Hardness and tribological behavior of the thin films were explored by microhardness indenter and pin on disc tribometer. The present result shows that micro-hardness of the BCN thin films with TiN interlayer is 23GPa. Friction coefficient of the thin films against GCr15 steel balls is about 0.3, adhersion and tribological properties of the BCN thin films with TiN interlayer are obviously better than the BCN monolayer thin films.
The BCN thin films with TiN interlayer were deposited on HSS and silicon (100) substrates by an arc enhanced reactive magnetron sputtering (AEMS). Microstructure of the thin films was characterized by meanings of XRD and FTIR. Adhersion to the sustrate of the thin films were characterized by scrach test. Hardness and tribological behavior of the thin films were explored by microhardness indenter and pin on disc tribometer. The present result shows that micro-hardness of the BCN thin films with TiN interlayer is 23GPa. Friction coefficient of the thin films against GCr15 steel balls is about 0.3, adhersion and tribological properties of the BCN thin films with TiN interlayer are obviously better than the BCN monolayer thin films.
2016, 45(2):507-514.
Abstract:
Octadecyltrichlorosilane (OTS) was grafted on titanium using self-assembly technique, after UV irradiation, its hydrophobic nature was changing. The calcium phosphate coatings was tunablely prepared by electrochemical deposition on functionalized titanium surface with different experiment conditions. The correlative structure and morphology of CaP coatings on titanium were characterized by X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM) under the preparation parameters. Its grain size under different conditions was calculated by Scherrer formula. The results indicated that the morphology of CaP coatings under different conditions were significant difference, and the grain sizes were ranged 12.46nm from 190.1nm. The study demonstrated that OTS functionalized titanium surface could be a controllable preparation of uniform and orderly nano CaP coatings, which is expected to improve the biocompatibility of implant materials.
Octadecyltrichlorosilane (OTS) was grafted on titanium using self-assembly technique, after UV irradiation, its hydrophobic nature was changing. The calcium phosphate coatings was tunablely prepared by electrochemical deposition on functionalized titanium surface with different experiment conditions. The correlative structure and morphology of CaP coatings on titanium were characterized by X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM) under the preparation parameters. Its grain size under different conditions was calculated by Scherrer formula. The results indicated that the morphology of CaP coatings under different conditions were significant difference, and the grain sizes were ranged 12.46nm from 190.1nm. The study demonstrated that OTS functionalized titanium surface could be a controllable preparation of uniform and orderly nano CaP coatings, which is expected to improve the biocompatibility of implant materials.
2016, 45(2):515-521.
Abstract:
During the complex parts of 3D printing processing, many processing defects, such as cracks, burr, and collapse, are beginning to form in the scanning around the corner. To reduce the scanning defects of different angle corners, the thermo–mechanical coupling field of different parts are simulated and the thermal and stress cloud pictures are analyzed. The relationshape about the machine tool's acceleration, the size of angle, the temperature of angle, temperature gradient and thermal stress are gained. The simulation results show that the thermal stress of corners not only rely on the machine tool's acceleration, but also contact closely with the angle of corners with both sides. The temperature results of simulation and the forming quality of the different angle of corners are verified by the experiment.
During the complex parts of 3D printing processing, many processing defects, such as cracks, burr, and collapse, are beginning to form in the scanning around the corner. To reduce the scanning defects of different angle corners, the thermo–mechanical coupling field of different parts are simulated and the thermal and stress cloud pictures are analyzed. The relationshape about the machine tool's acceleration, the size of angle, the temperature of angle, temperature gradient and thermal stress are gained. The simulation results show that the thermal stress of corners not only rely on the machine tool's acceleration, but also contact closely with the angle of corners with both sides. The temperature results of simulation and the forming quality of the different angle of corners are verified by the experiment.
2016, 45(2):522-528.
Abstract:
FeAl/Al2O3 composite coating is the most promising candidate for the tritium permeation barrier (TPB) of structural materials in the tritium breading blanket and auxiliary tritium handling system in fusion reactors. The preparation process of the FeAl/Al2O3 coating generally involves two steps of aluminization and oxidation. Interdiffusion occurs between Al atoms and Fe atoms on the base surface to form (Fe,Al) solid solution or Fe-Al intermetallic transition layer in the aluminization step. In the oxidation step, the aluminide layer surface is selectively oxidized to form Al2O3 film. FeAl/Al2O3 coating can be prepared by the technique of physical vapor deposition (PVD), chemical vapor deposition (CVD), hot-dipping aluminization (HDA), packing cementation (PC), plasma sputtering (PS) and electro-chemical deposition (ECD) et al. Relatively speaking, CVD, HDA and PC technique are promising in coating preparation, and have potentials to be selected as the candidate engineering preparation technique of FeAl/Al2O3 composite TPB coating in fusion reactors. Meanwhile, ECD technique is rather appealing for the preparation of FeAl/Al2O3 TPB coating because of its easy process controlling, stable coat performance and availability of coating complex-shaped structure.
FeAl/Al2O3 composite coating is the most promising candidate for the tritium permeation barrier (TPB) of structural materials in the tritium breading blanket and auxiliary tritium handling system in fusion reactors. The preparation process of the FeAl/Al2O3 coating generally involves two steps of aluminization and oxidation. Interdiffusion occurs between Al atoms and Fe atoms on the base surface to form (Fe,Al) solid solution or Fe-Al intermetallic transition layer in the aluminization step. In the oxidation step, the aluminide layer surface is selectively oxidized to form Al2O3 film. FeAl/Al2O3 coating can be prepared by the technique of physical vapor deposition (PVD), chemical vapor deposition (CVD), hot-dipping aluminization (HDA), packing cementation (PC), plasma sputtering (PS) and electro-chemical deposition (ECD) et al. Relatively speaking, CVD, HDA and PC technique are promising in coating preparation, and have potentials to be selected as the candidate engineering preparation technique of FeAl/Al2O3 composite TPB coating in fusion reactors. Meanwhile, ECD technique is rather appealing for the preparation of FeAl/Al2O3 TPB coating because of its easy process controlling, stable coat performance and availability of coating complex-shaped structure.
2016, 45(2):529-536.
Abstract:
This paper briefly introduce the methods of improving the material properties of tungsten and its alloy. Including the application status of major plastic processing methods (rolling, swaging, extrusion and severe plastic deformation methods), and the effect of these technologies on the properties (microstructure, mechanical property, recrystallization temperature and DBTT) have been summarized. Based on the analysis about powder mechanism of consolidation, a direct solidifying of tungsten powder via severe plastic deformation methods is researched.
This paper briefly introduce the methods of improving the material properties of tungsten and its alloy. Including the application status of major plastic processing methods (rolling, swaging, extrusion and severe plastic deformation methods), and the effect of these technologies on the properties (microstructure, mechanical property, recrystallization temperature and DBTT) have been summarized. Based on the analysis about powder mechanism of consolidation, a direct solidifying of tungsten powder via severe plastic deformation methods is researched.
