Volume 47,Issue 6,2018 Table of Contents
2018, 47(6):1655-1661.
Abstract:
The extrusion experiment at different extrusion parameters was studied, the effect of the different extrusion parameters on the microstructure and mechanical property of Mg-4.8Zn-1.2Y-0.4Zr magnesium alloy was described, based on the experimental results and analysis. The result shows that dynamic recrystallization has been observed after the hot extrusion process, the alloy grain which compares with as-cast alloy is refined. The phase of extruded alloy is W-phase, there is great morphology and distribution difference during different extrusion parameters. The microstructure and mechanical properties of magnesium alloy was affected by extrusion temperature and extrusion ratio during the hot extrusion process. When the extrusion ratio is the same, the number of recrystallization grains increases with the increasing of temperature, meanwhile recrystallization grains also has a tendency to grow up.When the extrusion temperature is 300 ℃, the comprehensive mechanics performance of alloy is the most excellent. The influence of extrusion ratio on the plasticity of the alloy is obvious, when extrusion ratio is 25, the alloy elongation of alloy increases significantly.
The extrusion experiment at different extrusion parameters was studied, the effect of the different extrusion parameters on the microstructure and mechanical property of Mg-4.8Zn-1.2Y-0.4Zr magnesium alloy was described, based on the experimental results and analysis. The result shows that dynamic recrystallization has been observed after the hot extrusion process, the alloy grain which compares with as-cast alloy is refined. The phase of extruded alloy is W-phase, there is great morphology and distribution difference during different extrusion parameters. The microstructure and mechanical properties of magnesium alloy was affected by extrusion temperature and extrusion ratio during the hot extrusion process. When the extrusion ratio is the same, the number of recrystallization grains increases with the increasing of temperature, meanwhile recrystallization grains also has a tendency to grow up.When the extrusion temperature is 300 ℃, the comprehensive mechanics performance of alloy is the most excellent. The influence of extrusion ratio on the plasticity of the alloy is obvious, when extrusion ratio is 25, the alloy elongation of alloy increases significantly.
2018, 47(6):1668-1676.
Abstract:
The surface integrity and notched fatigue property of a shot-peened single crystal superalloy were investigated. The surface texture of the peened material was determined using a white light interferometer, while the microstructural characterization was performed using a scan electron microscopy, high resolution transmission electron microscopy from the plane and cross-section view directions, micro-hardness tester and electron backscatter diffraction. The gains, expressed in term of high temperature fatigue limit, were established by rotating-bending fatigue tests and discussed in relation to the microstructure evolution in the shot peening states. This revealed that the beneficial effect provided by shot peening is more than 14.8% against as-machined in a temperature ranging from 760℃ to 850℃ because of the high-density tangled dislocation, cold work and disorientation. Furthermore, the stress concentration coefficient is reduced by the shot peening procedure while the average profile height Ra increases according to the calculation of the surface stress concentration.
The surface integrity and notched fatigue property of a shot-peened single crystal superalloy were investigated. The surface texture of the peened material was determined using a white light interferometer, while the microstructural characterization was performed using a scan electron microscopy, high resolution transmission electron microscopy from the plane and cross-section view directions, micro-hardness tester and electron backscatter diffraction. The gains, expressed in term of high temperature fatigue limit, were established by rotating-bending fatigue tests and discussed in relation to the microstructure evolution in the shot peening states. This revealed that the beneficial effect provided by shot peening is more than 14.8% against as-machined in a temperature ranging from 760℃ to 850℃ because of the high-density tangled dislocation, cold work and disorientation. Furthermore, the stress concentration coefficient is reduced by the shot peening procedure while the average profile height Ra increases according to the calculation of the surface stress concentration.
2018, 47(6):1677-1681.
Abstract:
The efficiency of a gas turbine engine is highly dependent upon the clearance between blades and engine case. To control the over-tip leakage, an abradable coating system is sprayed on the case surface. In the high temperature section, a ZrO2-8 wt% Y2O3 (YSZ) coating is usually applied as matrix. Pores in the coating are to enhance their abradability. In this study, poly-p-hydroxybenzoate (PHB) powder was used as a pore-forming material. To avoid burning loss of PHB during the spraying process, a sol-gel method was utilized to coat a TiO2 shell on the PHB powder surface. The characteristics of the coatings were investigated in this work, such as morphology, porosity, hardness and abradability. The results show that the coated PHB improved the porosity of the YSZ coating, and then decreased the coating hardness. Finally, an abradability test was utilized to exhibit the incursion depth increased with the increase of coating porosity.
The efficiency of a gas turbine engine is highly dependent upon the clearance between blades and engine case. To control the over-tip leakage, an abradable coating system is sprayed on the case surface. In the high temperature section, a ZrO2-8 wt% Y2O3 (YSZ) coating is usually applied as matrix. Pores in the coating are to enhance their abradability. In this study, poly-p-hydroxybenzoate (PHB) powder was used as a pore-forming material. To avoid burning loss of PHB during the spraying process, a sol-gel method was utilized to coat a TiO2 shell on the PHB powder surface. The characteristics of the coatings were investigated in this work, such as morphology, porosity, hardness and abradability. The results show that the coated PHB improved the porosity of the YSZ coating, and then decreased the coating hardness. Finally, an abradability test was utilized to exhibit the incursion depth increased with the increase of coating porosity.
2018, 47(6):1689-1694.
Abstract:
Microstructure evolution of SAF2205 duplex stainless steel during torsion deformation is studied at elevated temperatures (600°C, 800°C and 1000°C). The results of microstructure evolution indicate that different degrees’ recrystallization phenomena appear and the morphology of austenite is different for the deformed samples. The volume fraction of austenite decreases with the increase of deformation temperature. The fracture morphology of the deformed sample at 800°C is quite different from that of deformed sample at room temperature. It is shown that ductile fracture occurs when the torsion is carried out at the room temperature. Also, the equiaxed and parabolic dimples are observed on fracture surface. However, the fracture morphology of the deformed sample at 800°C is mainly covered by the intergranular fracture.
Microstructure evolution of SAF2205 duplex stainless steel during torsion deformation is studied at elevated temperatures (600°C, 800°C and 1000°C). The results of microstructure evolution indicate that different degrees’ recrystallization phenomena appear and the morphology of austenite is different for the deformed samples. The volume fraction of austenite decreases with the increase of deformation temperature. The fracture morphology of the deformed sample at 800°C is quite different from that of deformed sample at room temperature. It is shown that ductile fracture occurs when the torsion is carried out at the room temperature. Also, the equiaxed and parabolic dimples are observed on fracture surface. However, the fracture morphology of the deformed sample at 800°C is mainly covered by the intergranular fracture.
2018, 47(6):1716-1722.
Abstract:
After the optical micrography (OM) and scanning electron microscopy (SEM) observations, the grain size of primary α phase was measured via a quantitative metallography image analysis software. The effect of deformation temperature and strain rate on the microstructure was discussed. A Pi-sigma fuzzy neural network (FNN), in which the layers of neural networks were organized into a feed-forward system, was used to predict the flow stress and the grain size during isothermal compression of Ti-6Al-2Zr-2Sn-2Mo-1.5Cr-2Nb alloy. The comparisons of the predicted flow stress and grain size for the sample data or the non-sample data with the experimental results were given to train the models and confirm the validity in present study. The results show that the accuracy of prediction from the Pi-sigma FNN models is much high, and the Pi-sigma FNN approach can efficiently describe the non-linear and complex relationship of titanium alloys.
After the optical micrography (OM) and scanning electron microscopy (SEM) observations, the grain size of primary α phase was measured via a quantitative metallography image analysis software. The effect of deformation temperature and strain rate on the microstructure was discussed. A Pi-sigma fuzzy neural network (FNN), in which the layers of neural networks were organized into a feed-forward system, was used to predict the flow stress and the grain size during isothermal compression of Ti-6Al-2Zr-2Sn-2Mo-1.5Cr-2Nb alloy. The comparisons of the predicted flow stress and grain size for the sample data or the non-sample data with the experimental results were given to train the models and confirm the validity in present study. The results show that the accuracy of prediction from the Pi-sigma FNN models is much high, and the Pi-sigma FNN approach can efficiently describe the non-linear and complex relationship of titanium alloys.
6 Surface morphology controlled of tungsten and its thermal fatigue behavior under cyclic heat loading
2018, 47(6):1729-1733.
Abstract:
Thermal fatigue behavior under various cyclic heat loading is an important concern for tungsten as armor material in fusion devices. It may be significantly affected by its surface morphology. To address this issue, surface morphology controlled experiments have been performed on polycrystalline tungsten using an ECR plasma system and cyclic heat loading tests have been conducted upon the polished and modified samples using an electron beam facility. The results indicate that the surface topography has little effect on the characteristics of damage caused by the cycle plastic deformation during the cyclic heat loading. The micro-cracks and extrusions are formed in some grains after suffered 300 cyclic heat loading, which are aligned in different directions for varying grains. In addition, the modified specimens have fabricated both different triangular pyramid and homogeneous nanostructures by dry etching with different conditions. In this work, the cross-sectional surface of damage regions were analyzed and a set of schematic diagram was presented to explain the mechanism for the formation of micro-cracks and extrusions under cyclic heat loading.
Thermal fatigue behavior under various cyclic heat loading is an important concern for tungsten as armor material in fusion devices. It may be significantly affected by its surface morphology. To address this issue, surface morphology controlled experiments have been performed on polycrystalline tungsten using an ECR plasma system and cyclic heat loading tests have been conducted upon the polished and modified samples using an electron beam facility. The results indicate that the surface topography has little effect on the characteristics of damage caused by the cycle plastic deformation during the cyclic heat loading. The micro-cracks and extrusions are formed in some grains after suffered 300 cyclic heat loading, which are aligned in different directions for varying grains. In addition, the modified specimens have fabricated both different triangular pyramid and homogeneous nanostructures by dry etching with different conditions. In this work, the cross-sectional surface of damage regions were analyzed and a set of schematic diagram was presented to explain the mechanism for the formation of micro-cracks and extrusions under cyclic heat loading.
2018, 47(6):1734-1738.
Abstract:
Nd10.2Fe89.8-xCx (x = 0.0, 2.6, 5.2, 7.8) powder were prepared by arc smelting and ball milling. The structure and morphology of the powder were investigated by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The electromagnetic parameters of the powders were measured by vector network analyzer (VNA) at room temperature. Microwave absorbing properties of Nd10.2Fe89.8-xCx (x = 0.0, 2.6, 5.2, 7.8) depend sensitively on the compositions. The minimum absorption peak frequency shifts to the higher region upon the C content. The minimum reflectivity value of Nd10.2Fe84.6C5.2 can achieve to -13.2 dB at 5.2 GHz and the bandwidth of R < -10 dB achieve 1.2 GHz with the best matching thickness of 1.8 mm. The minimum absorption peak shifts towards lower frequency region with absorbing coating thickness increasing.
Nd10.2Fe89.8-xCx (x = 0.0, 2.6, 5.2, 7.8) powder were prepared by arc smelting and ball milling. The structure and morphology of the powder were investigated by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The electromagnetic parameters of the powders were measured by vector network analyzer (VNA) at room temperature. Microwave absorbing properties of Nd10.2Fe89.8-xCx (x = 0.0, 2.6, 5.2, 7.8) depend sensitively on the compositions. The minimum absorption peak frequency shifts to the higher region upon the C content. The minimum reflectivity value of Nd10.2Fe84.6C5.2 can achieve to -13.2 dB at 5.2 GHz and the bandwidth of R < -10 dB achieve 1.2 GHz with the best matching thickness of 1.8 mm. The minimum absorption peak shifts towards lower frequency region with absorbing coating thickness increasing.
8 Effect of Ca impurity on microstructures and mechanical properties of as-cast Al-5Mg filler metalsT
2018, 47(6):1739-1743.
Abstract:
Effects of Ca impurity on microstructures and mechanical properties of Al-5Mg filler metals were investigated with SEM, EDS, XRD, tensile test and impact test. The results indicate that the phase composition of Al-5Mg alloy is changed by the Ca impurity. It is observed that block-like (Ti,Cr)2Ca(Al,Mg)20 phase distributed discontinuously along the grain boundaries when the Ca content is less than 0.28%. When the content of Ca is over 0.28%, bar-like Al2Ca and block-like (Ti,Cr)2Ca(Al,Mg)20 combine together and distribute along the grain boundaries, and the amount and size of Ca-rich phase (both the bar-like and block-like) increase with the Ca content. Tensile strength of the Al-5Mg alloys increases firstly and then decreases with increasing Ca content, and the tensile strength gets to maximum value when the content of Ca is 0.28 wt%. The plasticity and fracture toughness decrease smoothly (Ca 0-0.28%) but then significantly (Ca>0.28%), and the tensile or impact fracture mode transform from the transgranular ductile fracture to the brittle cleavage fracture.
Effects of Ca impurity on microstructures and mechanical properties of Al-5Mg filler metals were investigated with SEM, EDS, XRD, tensile test and impact test. The results indicate that the phase composition of Al-5Mg alloy is changed by the Ca impurity. It is observed that block-like (Ti,Cr)2Ca(Al,Mg)20 phase distributed discontinuously along the grain boundaries when the Ca content is less than 0.28%. When the content of Ca is over 0.28%, bar-like Al2Ca and block-like (Ti,Cr)2Ca(Al,Mg)20 combine together and distribute along the grain boundaries, and the amount and size of Ca-rich phase (both the bar-like and block-like) increase with the Ca content. Tensile strength of the Al-5Mg alloys increases firstly and then decreases with increasing Ca content, and the tensile strength gets to maximum value when the content of Ca is 0.28 wt%. The plasticity and fracture toughness decrease smoothly (Ca 0-0.28%) but then significantly (Ca>0.28%), and the tensile or impact fracture mode transform from the transgranular ductile fracture to the brittle cleavage fracture.
2018, 47(6):1744-1748.
Abstract:
ZnS: Er/Yb nanocrystals were synthesized by the hydrothermal method using thioglycolic acid as a stabilizer. The crystalline phases, morphology, chemical bond states and photoluminescent properties of the nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoemission spectroscopy and fluorescence photometer. The results show that most prepared nanoparticles are spherical in shape with an average size of 5 nm, and have cubic zinc blende crystal structure. The emission spectrum of ZnS:Er/Yb nanocrystals excited at 270 nm displays three main peaks at 470 nm, 530 nm and 580 nm, and the intensity of fluorescence peaks is the strongest for nanocrystals prepared at 120 C. When ZnS:Er/Yb nanocrystals were excited at 980 nm, the emission peaks around 540 nm and 650 nm appeared, associated with the 4F3/2→4I15/2 and 4F9/2→4I15/2 of Er3+ ions transitions.
ZnS: Er/Yb nanocrystals were synthesized by the hydrothermal method using thioglycolic acid as a stabilizer. The crystalline phases, morphology, chemical bond states and photoluminescent properties of the nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoemission spectroscopy and fluorescence photometer. The results show that most prepared nanoparticles are spherical in shape with an average size of 5 nm, and have cubic zinc blende crystal structure. The emission spectrum of ZnS:Er/Yb nanocrystals excited at 270 nm displays three main peaks at 470 nm, 530 nm and 580 nm, and the intensity of fluorescence peaks is the strongest for nanocrystals prepared at 120 C. When ZnS:Er/Yb nanocrystals were excited at 980 nm, the emission peaks around 540 nm and 650 nm appeared, associated with the 4F3/2→4I15/2 and 4F9/2→4I15/2 of Er3+ ions transitions.
10 Fabrication of Carbon Encapsulated ZrC Nanoparticles by Electrical Explosion of Zr Wire in Ethanol
2018, 47(6):1749-1752.
Abstract:
The method of electrical explosion of metal wire in organic liquid was adopted to prepare carbon encapsulated nanoparticles. In the medium of absolute ethyl alcohol, under the high-voltage pulse current (HVPC), the high purity zirconium wire became fusion, gasification, expansion and explosion, accompanied with separating of carbon out of ethanol and reaction of carbon and zirconium, carbon encapsulated ZrC nanoparticles formed. The energy, voltage and current in the experiments were measured to analyze the influence of them on the products. The products were analyzed by X-ray diffraction technique (XRD), transmission electron microscopy (TEM) and high power transmission electron microscopy (HTEM). The results show that the carbon encapsulated ZrC nanoparticles were fabricated successfully. The diameter range between 10nm-150nm. For the voltage of 4kv, 8kv and 12kv, the average size of the products is 24.9nm, 41.4nm and 43.9nm, respectively. Finally, the procedure and mechanism of fabrication of the carbon encapsulated ZrC nanoparticles were discussed preliminarily.
The method of electrical explosion of metal wire in organic liquid was adopted to prepare carbon encapsulated nanoparticles. In the medium of absolute ethyl alcohol, under the high-voltage pulse current (HVPC), the high purity zirconium wire became fusion, gasification, expansion and explosion, accompanied with separating of carbon out of ethanol and reaction of carbon and zirconium, carbon encapsulated ZrC nanoparticles formed. The energy, voltage and current in the experiments were measured to analyze the influence of them on the products. The products were analyzed by X-ray diffraction technique (XRD), transmission electron microscopy (TEM) and high power transmission electron microscopy (HTEM). The results show that the carbon encapsulated ZrC nanoparticles were fabricated successfully. The diameter range between 10nm-150nm. For the voltage of 4kv, 8kv and 12kv, the average size of the products is 24.9nm, 41.4nm and 43.9nm, respectively. Finally, the procedure and mechanism of fabrication of the carbon encapsulated ZrC nanoparticles were discussed preliminarily.
2018, 47(6):1662-1667.
Abstract:
We perform theoretical investigation on mechanisms of LiD/LiH/LiT+H2O reactions with second order perturbation theory (MP2). Calculations of enthalpy change and reaction rate constant are in agreement with experimental data and other theoretical values. Results show that two reaction channels exist for LiD+H2O reaction, channel 1 is the main reaction channel. Kinetic Isotope Effect (KIE) is not so large however fracture of isotope bond takes place in the reaction, which is noticeably different from theoretical maximums of primary isotope effect. Individual contributions of KIE effect are listed as follows ηvib>ηrot>ηtun>ηpot>ηtrans, indicating that main contribution of isotope effect results from vibration factor.
We perform theoretical investigation on mechanisms of LiD/LiH/LiT+H2O reactions with second order perturbation theory (MP2). Calculations of enthalpy change and reaction rate constant are in agreement with experimental data and other theoretical values. Results show that two reaction channels exist for LiD+H2O reaction, channel 1 is the main reaction channel. Kinetic Isotope Effect (KIE) is not so large however fracture of isotope bond takes place in the reaction, which is noticeably different from theoretical maximums of primary isotope effect. Individual contributions of KIE effect are listed as follows ηvib>ηrot>ηtun>ηpot>ηtrans, indicating that main contribution of isotope effect results from vibration factor.
2018, 47(6):1682-1688.
Abstract:
The preparation of pure and Ni-doped ZnO from different ingredient by coprecipitation method. Then the Comparison on the response of pure and Ni-doped ZnO sensors on different Ni concentration to 20ppm acetone was investigate for the sake of finding Ni dosage of the sensors under optimum response.OnSthisSbasis, Au was added into this sensors for activate these.TheSexperimentalSresultSindicatedSthat 1mol% Ni-doped ZnO sensors are better than other sensor without Au activation.Further 0.03mol% Au activated 1mol% Ni-doped ZnO has the showStheShighest acetone gas response in all sensors and it also maintain high selective over ethanol,formaldehyde,acetone and rapid response-recovery time under this condition.
The preparation of pure and Ni-doped ZnO from different ingredient by coprecipitation method. Then the Comparison on the response of pure and Ni-doped ZnO sensors on different Ni concentration to 20ppm acetone was investigate for the sake of finding Ni dosage of the sensors under optimum response.OnSthisSbasis, Au was added into this sensors for activate these.TheSexperimentalSresultSindicatedSthat 1mol% Ni-doped ZnO sensors are better than other sensor without Au activation.Further 0.03mol% Au activated 1mol% Ni-doped ZnO has the showStheShighest acetone gas response in all sensors and it also maintain high selective over ethanol,formaldehyde,acetone and rapid response-recovery time under this condition.
2018, 47(6):1695-1699.
Abstract:
In order to prepare high performance tungsten used as plasma face material, trace amount of ZrC was added to tungsten, and the densification behavior, properties and microstructure evolution of W-ZrC composites sintered at temperatures in the rang 1150 - 2000°C with flowing hydrogen atmosphere were investigated systematically. Results show that W-ZrC composite powders begin to form fine tungsten grains at 1300°C. The growth rate of grains is high at temperatures below 1600°C, and then slows down. The maximum relative density and tensile strength are 99.6% and 460MPa respectively under the optimum sintering process. ZrC particles are uniformly dispersed at grain boundaries and in grains interior with particle size from 0.1μm to 2 μm. Minor ZrC can effectively prevent the migration of grain boundaries and refine grain sizes from 100 μm of pure tungsten to 30 μm of W-ZrC composites. Minor ZrC can change the fracture mode and improve the strength and toughness of tungsten.
In order to prepare high performance tungsten used as plasma face material, trace amount of ZrC was added to tungsten, and the densification behavior, properties and microstructure evolution of W-ZrC composites sintered at temperatures in the rang 1150 - 2000°C with flowing hydrogen atmosphere were investigated systematically. Results show that W-ZrC composite powders begin to form fine tungsten grains at 1300°C. The growth rate of grains is high at temperatures below 1600°C, and then slows down. The maximum relative density and tensile strength are 99.6% and 460MPa respectively under the optimum sintering process. ZrC particles are uniformly dispersed at grain boundaries and in grains interior with particle size from 0.1μm to 2 μm. Minor ZrC can effectively prevent the migration of grain boundaries and refine grain sizes from 100 μm of pure tungsten to 30 μm of W-ZrC composites. Minor ZrC can change the fracture mode and improve the strength and toughness of tungsten.
2018, 47(6):1700-1707.
Abstract:
The hot deformation behavior and processing maps of as-homogenized Mg-Gd-Y-Zn-Mn alloy were investigated by hot compression tests performed at 350-500°C and strain rates ranging from 0.001/ s to 1/ s . The constitutive equation was established using hyperbolic law, and the activation energy of the alloy was calculated to be about 260.94 kJ/mol. Based on the dynamic material model, processing maps of as-homogenized Mg-Gd-Y-Zn-Mn deformed at strain values of 0.6,1.2 were drawn to study the hot workability of the alloy. The processing map developed at a strain of 1.2 shows two safety domains: one occurring at 460–500°C and strain rates ranging from 0.001 /s to 1 /s; the other occurring at 350–500°C, and strain rate ranging from 0.001/s to 0.005/s. The corresponding microstructure evolutions, with particular emphasis on the deformation mechanism of long-period stacking ordered phase (LPSO) in this alloy, were also discussed.
The hot deformation behavior and processing maps of as-homogenized Mg-Gd-Y-Zn-Mn alloy were investigated by hot compression tests performed at 350-500°C and strain rates ranging from 0.001/ s to 1/ s . The constitutive equation was established using hyperbolic law, and the activation energy of the alloy was calculated to be about 260.94 kJ/mol. Based on the dynamic material model, processing maps of as-homogenized Mg-Gd-Y-Zn-Mn deformed at strain values of 0.6,1.2 were drawn to study the hot workability of the alloy. The processing map developed at a strain of 1.2 shows two safety domains: one occurring at 460–500°C and strain rates ranging from 0.001 /s to 1 /s; the other occurring at 350–500°C, and strain rate ranging from 0.001/s to 0.005/s. The corresponding microstructure evolutions, with particular emphasis on the deformation mechanism of long-period stacking ordered phase (LPSO) in this alloy, were also discussed.
2018, 47(6):1708-1715.
Abstract:
Tungsten heavy alloys (WHAs) achieve a special combination of properties, such as high density, high mechanical strength and good corrosion resistance in the industrial and military applications. In this study, the corrosion performance of two WHAs, 90%W-6%Ni-4%Cu and 95%W-3.5%Ni-1.5%Fe has been investigated by immersion test and electrochemical test. The AFM results indicated the attack would be on the W phase in W-Ni-Cu alloy when it generated galvanic corrosion, W-Ni-Fe alloy revealed opposite result. Potentiodynamic polarization measurement showed pH value is an important factor in corrosion rate. The two types alloys showed relatively lower corrosion rates in DI water, as compared to 0.6MHCl solution. The corrosion mechanism was involved in the release of the metallic components and generation of corrosion products in term of SEM and EDX.
Tungsten heavy alloys (WHAs) achieve a special combination of properties, such as high density, high mechanical strength and good corrosion resistance in the industrial and military applications. In this study, the corrosion performance of two WHAs, 90%W-6%Ni-4%Cu and 95%W-3.5%Ni-1.5%Fe has been investigated by immersion test and electrochemical test. The AFM results indicated the attack would be on the W phase in W-Ni-Cu alloy when it generated galvanic corrosion, W-Ni-Fe alloy revealed opposite result. Potentiodynamic polarization measurement showed pH value is an important factor in corrosion rate. The two types alloys showed relatively lower corrosion rates in DI water, as compared to 0.6MHCl solution. The corrosion mechanism was involved in the release of the metallic components and generation of corrosion products in term of SEM and EDX.
2018, 47(6):1723-1728.
Abstract:
This report shows that the variation of metallic particle size alters the combustion characteristics and dynamic response of W-PTFE-Al composites. Combustion test results show that the reaction energy of W(7μm)-PTFE(40μm)-Al(1μm) reached 4570.2J/g in argon environment and 9848.1J/g in oxygen environment, indicating fine aluminum and coarse tungsten contribute to the increase of reaction energy. Under dynamic loading, the deflagration time of all four kinds of W-PTFE-Al composites is longer than 500μs. With decreased Al particle size, the insensitivity of W-PTFE-Al composites to impact shows a decreasing tendency due to the absorbed critical energy before reaction decreases by 14.0%. With decreased W particles size, the insensitivity of W-PTFE-Al composites to impact enhances due to the absorbed critical energy before reaction increases by 34.8%. The dynamic compression results show that, the ultimate strength of W-PTFE-Al composites increases by 8.0% with Al particle size changing from 10μm to 1μm, but decreases by 10.2% with W particle size changing from 7μm to 100nm.
This report shows that the variation of metallic particle size alters the combustion characteristics and dynamic response of W-PTFE-Al composites. Combustion test results show that the reaction energy of W(7μm)-PTFE(40μm)-Al(1μm) reached 4570.2J/g in argon environment and 9848.1J/g in oxygen environment, indicating fine aluminum and coarse tungsten contribute to the increase of reaction energy. Under dynamic loading, the deflagration time of all four kinds of W-PTFE-Al composites is longer than 500μs. With decreased Al particle size, the insensitivity of W-PTFE-Al composites to impact shows a decreasing tendency due to the absorbed critical energy before reaction decreases by 14.0%. With decreased W particles size, the insensitivity of W-PTFE-Al composites to impact enhances due to the absorbed critical energy before reaction increases by 34.8%. The dynamic compression results show that, the ultimate strength of W-PTFE-Al composites increases by 8.0% with Al particle size changing from 10μm to 1μm, but decreases by 10.2% with W particle size changing from 7μm to 100nm.
2018, 47(6):1753-1759.
Abstract:
A crystal plasticity constitutive model for Ti3Al single crystal was established based on slip deformation mechanism within the frame of crystal plasticity theory, and it was compiled to a program to describe it by means of secondary development of ABAQUS/UMAT user subroutine. Then we applied it to simulate the mechanical behaviors of Ti3Al single crystal with different orientations during unidirectional compression deformation. The activation of slip systems and the interaction between activation and orientation has been analyzed. The simulation results show that basal slip of (0001)<112(—)0>, prismatic slip of {101(—)0}<112(—)0> , and pyramidal slip of {112(—)1}<112(—)6> can be activated. However, there are dramatic diference on the ease or complexity of activation of various slip systems, which is due to the difference of critical shearing stress and schmid factor. It is difficult for basal slip and pyramidal slip to be activated because of their larger critical shearing stress, which leads that the activation of basal slip and pyramidal slip just occurs with larger schmid factor. Pyramidal slip systems only can be initiated when compression axis is close to [0001] direction due to the maximum shearing critical shearing stress, especially. Prismatic slip is much easier to be activated and also has the largest contribution to plastic deformation. Furthermore, the simulation results were compared and in good agreement with the experimental results.
A crystal plasticity constitutive model for Ti3Al single crystal was established based on slip deformation mechanism within the frame of crystal plasticity theory, and it was compiled to a program to describe it by means of secondary development of ABAQUS/UMAT user subroutine. Then we applied it to simulate the mechanical behaviors of Ti3Al single crystal with different orientations during unidirectional compression deformation. The activation of slip systems and the interaction between activation and orientation has been analyzed. The simulation results show that basal slip of (0001)<112(—)0>, prismatic slip of {101(—)0}<112(—)0> , and pyramidal slip of {112(—)1}<112(—)6> can be activated. However, there are dramatic diference on the ease or complexity of activation of various slip systems, which is due to the difference of critical shearing stress and schmid factor. It is difficult for basal slip and pyramidal slip to be activated because of their larger critical shearing stress, which leads that the activation of basal slip and pyramidal slip just occurs with larger schmid factor. Pyramidal slip systems only can be initiated when compression axis is close to [0001] direction due to the maximum shearing critical shearing stress, especially. Prismatic slip is much easier to be activated and also has the largest contribution to plastic deformation. Furthermore, the simulation results were compared and in good agreement with the experimental results.
2018, 47(6):1760-1765.
Abstract:
The dynamic tensile behavior of a newly developed Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-Si alloy (referred as TC21) over a wide range of strain rates from quasi-static to dynamic regimes (0.001-1250s-1) at different temperatures are experimentally investigated. A split Hopkinson tension bar apparatus and a static material testing system are utilized to obtain the stress-strain response under uniaxial tension loading condition. The experimental results indicate that the tensile behavior of TC21 titanium alloy is dependent on the strain rate and temperature. The initial yield stress increases with increasing strain rate. The effects of strain rate and temperature on the initial yield behavior are studied by introducing two rate sensitivity parameters. The phenomenologically based constitutive model (Johnson-Cook model) is suitably modified to describe the dynamic tensile behavior of TC21 titanium alloy. The predicted results of modified model are in good agreement with the experimental data subjected to the investigated range of strain rates and temperatures.
The dynamic tensile behavior of a newly developed Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-Si alloy (referred as TC21) over a wide range of strain rates from quasi-static to dynamic regimes (0.001-1250s-1) at different temperatures are experimentally investigated. A split Hopkinson tension bar apparatus and a static material testing system are utilized to obtain the stress-strain response under uniaxial tension loading condition. The experimental results indicate that the tensile behavior of TC21 titanium alloy is dependent on the strain rate and temperature. The initial yield stress increases with increasing strain rate. The effects of strain rate and temperature on the initial yield behavior are studied by introducing two rate sensitivity parameters. The phenomenologically based constitutive model (Johnson-Cook model) is suitably modified to describe the dynamic tensile behavior of TC21 titanium alloy. The predicted results of modified model are in good agreement with the experimental data subjected to the investigated range of strain rates and temperatures.
2018, 47(6):1766-1770.
Abstract:
Al-6.2Zn-2.3Mg and Al-5.0Zn-3.0Mg alloys were prepared, and then solution-aging treatment proceeded. Based on the empirical electron theory of solids and molecules (EET), in this paper, the valence electron structures of solid solutions of alloys were calculated, and then the effect of Zn/Mg on aging-precipitation behavior of Al-Zn-Mg alloys was studied. It is shown that solid solution a-Al-Zn-Mg prior formed during solid solution of Al-6.2Zn-2.3Mg alloy provides the condition for the formation of GP Zone of h precipitation sequence. Only h precipitation sequence is started, so aging-hardening behavior of Al-6.2Zn-2.3Mg alloy appears obvious two peaks characteristic. While the two solid solutions a-Al-Zn-Mg and a-Al-Mg-Zn-Mg-Al formed during solid solution of Al-5.0Zn-3.0Mg alloy provide the condition for the formation of GP Zone of h and T precipitation sequence, respectively. These two precipitation sequences have so many different at aging progress, precipitation time and their strengthening effects of strengthening phases, transforming time and caused strengthening effects weakness of strengthening phases, so these two precipitation sequences of h and T are started when aging, aging-hardening behavior of Al-5.0Zn-3.0Mg alloy does not appears obvious two peaks characteristic.
Al-6.2Zn-2.3Mg and Al-5.0Zn-3.0Mg alloys were prepared, and then solution-aging treatment proceeded. Based on the empirical electron theory of solids and molecules (EET), in this paper, the valence electron structures of solid solutions of alloys were calculated, and then the effect of Zn/Mg on aging-precipitation behavior of Al-Zn-Mg alloys was studied. It is shown that solid solution a-Al-Zn-Mg prior formed during solid solution of Al-6.2Zn-2.3Mg alloy provides the condition for the formation of GP Zone of h precipitation sequence. Only h precipitation sequence is started, so aging-hardening behavior of Al-6.2Zn-2.3Mg alloy appears obvious two peaks characteristic. While the two solid solutions a-Al-Zn-Mg and a-Al-Mg-Zn-Mg-Al formed during solid solution of Al-5.0Zn-3.0Mg alloy provide the condition for the formation of GP Zone of h and T precipitation sequence, respectively. These two precipitation sequences have so many different at aging progress, precipitation time and their strengthening effects of strengthening phases, transforming time and caused strengthening effects weakness of strengthening phases, so these two precipitation sequences of h and T are started when aging, aging-hardening behavior of Al-5.0Zn-3.0Mg alloy does not appears obvious two peaks characteristic.
2018, 47(6):1771-1778.
Abstract:
In this study, the burn-resistant property of laser solid forming (LSF) of Ti-25V-15Cr alloy was studied, and compared with that of forging Ti40 alloy. The burn-resistant mechanism was disclosed by combining the analysis of the microstructure of the alloy and the combustion products. The results showed that the burning rate of Ti-25V-15Cr alloy is slightly lower than that of forging Ti40 alloy. The combustion products of Ti-25V-15Cr alloy and Ti40 alloy are mainly composed of a mixture of Ti oxide and V oxide, and the substrate. The area of the Oxide in the combustion product zone of LSF Ti-25V-15Cr is a little smaller than that of forging Ti40. Moreover, the distinct segregation of V and Cr in the grain boundary and subgrain boundary was found in LSF Ti-25V-15Cr alloy. The formation of the dendrites and subgrains in LSF Ti-25V-15Cr increases the micro-defect and leads to the better diffusion capacity of V and Cr, which is responsible for the better resistance to the burning of LSF Ti-25V-15Cr than that of forging Ti40.
In this study, the burn-resistant property of laser solid forming (LSF) of Ti-25V-15Cr alloy was studied, and compared with that of forging Ti40 alloy. The burn-resistant mechanism was disclosed by combining the analysis of the microstructure of the alloy and the combustion products. The results showed that the burning rate of Ti-25V-15Cr alloy is slightly lower than that of forging Ti40 alloy. The combustion products of Ti-25V-15Cr alloy and Ti40 alloy are mainly composed of a mixture of Ti oxide and V oxide, and the substrate. The area of the Oxide in the combustion product zone of LSF Ti-25V-15Cr is a little smaller than that of forging Ti40. Moreover, the distinct segregation of V and Cr in the grain boundary and subgrain boundary was found in LSF Ti-25V-15Cr alloy. The formation of the dendrites and subgrains in LSF Ti-25V-15Cr increases the micro-defect and leads to the better diffusion capacity of V and Cr, which is responsible for the better resistance to the burning of LSF Ti-25V-15Cr than that of forging Ti40.
21 Investigation about microstructures and typical mechanical properties of overheated K424 superalloy
2018, 47(6):1779-1785.
Abstract:
Stress rupture test at 975℃/196MPa and room temperature tensile test were conducted in standard heat-treated K424 alloy after overheating at different conditions (1050℃~1150℃/2h, air cooling), the characterization of microstructures and fracture features were then investigated. The results showed that mechanical properties of standard heat-treated K424 alloy were only slightly lower after overheating at 1050℃~1150℃ for 2h, the mechanical property indexes were obviously higher than the values in standard. Microstructural characterization indicated that grain morphology, grain boundary morphology and γ’ phase in the interdendritic regions showed no significant change after overheating at different conditions. The more cuboidal primary γ’ phase and the precipitation of secondary γ’ phase in γ channel were responsible for the slightly diminished mechanical properties after overheating. In addition, the high temperature and room temperature fracture mechanisms of overheated K424 alloy were also discussed.
Stress rupture test at 975℃/196MPa and room temperature tensile test were conducted in standard heat-treated K424 alloy after overheating at different conditions (1050℃~1150℃/2h, air cooling), the characterization of microstructures and fracture features were then investigated. The results showed that mechanical properties of standard heat-treated K424 alloy were only slightly lower after overheating at 1050℃~1150℃ for 2h, the mechanical property indexes were obviously higher than the values in standard. Microstructural characterization indicated that grain morphology, grain boundary morphology and γ’ phase in the interdendritic regions showed no significant change after overheating at different conditions. The more cuboidal primary γ’ phase and the precipitation of secondary γ’ phase in γ channel were responsible for the slightly diminished mechanical properties after overheating. In addition, the high temperature and room temperature fracture mechanisms of overheated K424 alloy were also discussed.
2018, 47(6):1786-1792.
Abstract:
A friction stir welded 2099-T83 extruded Al-Li alloy has been characterized in terms of microstructure and crystallographic texture. Optical microscopy, scanning electron microscopy and transmission electron microscopy were applied to investigate the microstructure and hardness. Hardness test revealed the W-shaped profile in weld zone and reach to minimum in HMAZ. Base metal shows a partial recrystallization with T1 phase and δ′ phase in grain and grain boundary. The grain size in welding zone is smaller than base metal,and the precipitates what observed in base metal dissolved and transformed into δ′ phase in welding zone. Furthermore crystallographic texture analysis by electron backscatter diffraction indicated that the base metal exist {112}<111>copper ,{123}<634>S and {001}<100> cube texture. The nugget zone presented {001}<110> rotated-cube texture as it experienced dynamic recrystallization. The thermo-mechanically affected zone and heat affected zone are dominated by {112}<110> and {112}<111>texture respectively , and both of them exist the weak {001}<120> texture.
A friction stir welded 2099-T83 extruded Al-Li alloy has been characterized in terms of microstructure and crystallographic texture. Optical microscopy, scanning electron microscopy and transmission electron microscopy were applied to investigate the microstructure and hardness. Hardness test revealed the W-shaped profile in weld zone and reach to minimum in HMAZ. Base metal shows a partial recrystallization with T1 phase and δ′ phase in grain and grain boundary. The grain size in welding zone is smaller than base metal,and the precipitates what observed in base metal dissolved and transformed into δ′ phase in welding zone. Furthermore crystallographic texture analysis by electron backscatter diffraction indicated that the base metal exist {112}<111>copper ,{123}<634>S and {001}<100> cube texture. The nugget zone presented {001}<110> rotated-cube texture as it experienced dynamic recrystallization. The thermo-mechanically affected zone and heat affected zone are dominated by {112}<110> and {112}<111>texture respectively , and both of them exist the weak {001}<120> texture.
2018, 47(6):1793-1799.
Abstract:
The effects of different initial energy storage on the properties of Al-11.54Zn-3.51Mg-2.26Cu-0.24Zr super high strength aluminum alloy at different heating rates were explored by electrical conductivity,hardness EBSD and XRD analysis. The results show that the conductivity increases and then decreases with the increase of temperature, the hardness decreases and then increases with the increase of temperature.The dislocation density of the alloy is reduced to 0 when the annealing temperature is between 300 ℃ and 450 ℃, and the dislocation is re produced when the annealing temperature reaches 470 ℃. The average size of alloy decreases slightly during heating annealing to 300 ℃ grain, grain size of the alloy annealed to 470 ℃ increased significantly. Improving the initial deformation energy storage, the average grain size and low angle grain boundaries has been significantly reduced, dislocation and grain boundary strengthening has improved.
The effects of different initial energy storage on the properties of Al-11.54Zn-3.51Mg-2.26Cu-0.24Zr super high strength aluminum alloy at different heating rates were explored by electrical conductivity,hardness EBSD and XRD analysis. The results show that the conductivity increases and then decreases with the increase of temperature, the hardness decreases and then increases with the increase of temperature.The dislocation density of the alloy is reduced to 0 when the annealing temperature is between 300 ℃ and 450 ℃, and the dislocation is re produced when the annealing temperature reaches 470 ℃. The average size of alloy decreases slightly during heating annealing to 300 ℃ grain, grain size of the alloy annealed to 470 ℃ increased significantly. Improving the initial deformation energy storage, the average grain size and low angle grain boundaries has been significantly reduced, dislocation and grain boundary strengthening has improved.
2018, 47(6):1800-1805.
Abstract:
XRD, SEM+EDS and electrochemical tester at 323K were adopted to measure phase structure and electrochemical properties of Ti1.8(VFe)CrNi0.2+x.wt%LaNi5 hydrogen storage composite. It has showed that main phase, which is BCC structure with alloy’s cellular crystal and Cr-Ni-Ti-Fe with BCT structure, transformed into Ti-V-Cr-Fe-Ni which is main phase of BCC structure with dentrite crystal. Electrochemical properties show that activity and discharge capacity and so on is changed regularly. When x is 5, activity and discharge capacity of the composite alloy is the best of all, which is active by 9 cycle time and the discharge capacity reach 360mAh/g. It can be certain that the formation of rod-like crystal and synergistic reaction between the second phase Cr-Ni-Ti-Fe phase and the main phase of BCC structure plays the most important role in ipproving the alloy’s electrochemical properties.
XRD, SEM+EDS and electrochemical tester at 323K were adopted to measure phase structure and electrochemical properties of Ti1.8(VFe)CrNi0.2+x.wt%LaNi5 hydrogen storage composite. It has showed that main phase, which is BCC structure with alloy’s cellular crystal and Cr-Ni-Ti-Fe with BCT structure, transformed into Ti-V-Cr-Fe-Ni which is main phase of BCC structure with dentrite crystal. Electrochemical properties show that activity and discharge capacity and so on is changed regularly. When x is 5, activity and discharge capacity of the composite alloy is the best of all, which is active by 9 cycle time and the discharge capacity reach 360mAh/g. It can be certain that the formation of rod-like crystal and synergistic reaction between the second phase Cr-Ni-Ti-Fe phase and the main phase of BCC structure plays the most important role in ipproving the alloy’s electrochemical properties.
2018, 47(6):1806-1811.
Abstract:
The ultra-fine grain(UFG) material by Equal Channel Angular Pressing (ECAP) has attracted attention for excellent mechanical performance. The fatigue properties of UFG by ECAPSareScriticalSto wide application. The fatigue properties of ultra-fine grain high purity(HP) and low purity(LP) copper by ECAP were investigated by fatigue tests conducted in air, at symmetrical loading ratio R= -1. The cyclic stress-strain response, fatigue life and grain orientation distribution before and after fatigue were analyzed. The relationship between purity and fatigue stability of ultra-fine grain copper were discussed. The results showed that the stress-controlled fatigue life of UFG low purity copper is longer about 1.6~2.0 times than that of their coarse grain (CG) counterparts under any stress amplitude. On the other hand, the fatigue curve of UFG high purity copper shows different characteristics. TheSfatigueScyclesSto failure of UFG Hp copper is strongly dependent upon the applied stress amplitude and decrease sharply withSstress amplitude decreasing. Under lower cyclic stresses, UFG Hp copper exhibitsSlower fatigue lives. Cyclic stress-strain response of UFG Cu under stress-controlled loading change from cyclic softening to cyclic hardening with stress amplitude decreasing. The UFG low purity copper shows a relatively high cyclic strain hardening exponent, hardeningShardeningScoefficient and fatigue stability with respect to the UFG high purity copper, because the impurity hinder grain rotation and dislocation motion, decline recovery rate, and reduce grain orientation modifies.
The ultra-fine grain(UFG) material by Equal Channel Angular Pressing (ECAP) has attracted attention for excellent mechanical performance. The fatigue properties of UFG by ECAPSareScriticalSto wide application. The fatigue properties of ultra-fine grain high purity(HP) and low purity(LP) copper by ECAP were investigated by fatigue tests conducted in air, at symmetrical loading ratio R= -1. The cyclic stress-strain response, fatigue life and grain orientation distribution before and after fatigue were analyzed. The relationship between purity and fatigue stability of ultra-fine grain copper were discussed. The results showed that the stress-controlled fatigue life of UFG low purity copper is longer about 1.6~2.0 times than that of their coarse grain (CG) counterparts under any stress amplitude. On the other hand, the fatigue curve of UFG high purity copper shows different characteristics. TheSfatigueScyclesSto failure of UFG Hp copper is strongly dependent upon the applied stress amplitude and decrease sharply withSstress amplitude decreasing. Under lower cyclic stresses, UFG Hp copper exhibitsSlower fatigue lives. Cyclic stress-strain response of UFG Cu under stress-controlled loading change from cyclic softening to cyclic hardening with stress amplitude decreasing. The UFG low purity copper shows a relatively high cyclic strain hardening exponent, hardeningShardeningScoefficient and fatigue stability with respect to the UFG high purity copper, because the impurity hinder grain rotation and dislocation motion, decline recovery rate, and reduce grain orientation modifies.
2018, 47(6):1812-1817.
Abstract:
The surfacing welding is the common repairing technology and an effective way for the repair of local damage occurs at the magnesium equipment surfaces. The effects of varying contents of the yttrium on the dry sliding wear behavior of surfacing AZ91 magnesium alloys were investigated in this work. The results demonstrated that the surfacing AZ91 alloy without yttrium addition exhibited poor wear resistance, due to the massive intermetallic β- Mg17Al12 phases. With the addition of yttrium, wear resistance was improved resulting from the decrease of size and quantity of the β phase, which reduced the alloy hardness and decreased the subsurface metal deformation degree caused by friction. Three primary wear mechanisms were observed: abrasion, oxidation and delamination.
The surfacing welding is the common repairing technology and an effective way for the repair of local damage occurs at the magnesium equipment surfaces. The effects of varying contents of the yttrium on the dry sliding wear behavior of surfacing AZ91 magnesium alloys were investigated in this work. The results demonstrated that the surfacing AZ91 alloy without yttrium addition exhibited poor wear resistance, due to the massive intermetallic β- Mg17Al12 phases. With the addition of yttrium, wear resistance was improved resulting from the decrease of size and quantity of the β phase, which reduced the alloy hardness and decreased the subsurface metal deformation degree caused by friction. Three primary wear mechanisms were observed: abrasion, oxidation and delamination.
2018, 47(6):1818-1823.
Abstract:
In this study arc erosion properties of Cu-30vol%gaphite, Cu-30vol%WS2 and Cu-30vol%MoS2 composites were investigated. The results demonstrated that graphite cannot beSmelted and mainly lost in the form of oxidation during the arc discharge process because of its extremely high melting point. In contrast, WS2 and MoS2 were melted and even reacted with Cu matrix due to the high temperature caused by arc discharge. Therefore, the arc erosion resistance of Cu-30vol%gaphite composite was better than those of Cu-30vol%WS2 and Cu-30vol%MoS2 composites. The main arc erosion mechanisms of Cu-based self-lubricating composites were found to be oxidation, melting, ejecting, internal chemical reaction and fatigue peeling.
In this study arc erosion properties of Cu-30vol%gaphite, Cu-30vol%WS2 and Cu-30vol%MoS2 composites were investigated. The results demonstrated that graphite cannot beSmelted and mainly lost in the form of oxidation during the arc discharge process because of its extremely high melting point. In contrast, WS2 and MoS2 were melted and even reacted with Cu matrix due to the high temperature caused by arc discharge. Therefore, the arc erosion resistance of Cu-30vol%gaphite composite was better than those of Cu-30vol%WS2 and Cu-30vol%MoS2 composites. The main arc erosion mechanisms of Cu-based self-lubricating composites were found to be oxidation, melting, ejecting, internal chemical reaction and fatigue peeling.
2018, 47(6):1824-1829.
Abstract:
By using NH4VO3 as raw material, high-active V2O3 cathode pellets were prepared by reduction with coal gas and in-situ sintering, then were directly reduced to metallic vanadium by rapid electro-deoxidization in molten fluorides. The mechanism of V2O3 electro-deoxidization was studied by cyclic voltammetry experiments and constant potential electrolysis experiments. The results indicate that the rapid electro-deoxidization of V2O3 can be realized in molten fluorides, metallic vanadium containing 0.218 wt% oxygen can be obtained after 4 h electrolysis. The in-suit formation of aluminium-oxygen-fluorine complex ions, which further forming aluminum metal in deoxidation reaction zone, caused aluminum thermal reduction reaction of V2O3 cathode. So direct electro-deoxidation reduction and aluminum thermal reaction of V2O3 both existed in the deoxidation process of V2O3 cathode, and the latter reaction played a key role in acceleration action. Electro-deoxidization process of V2O3 cathode can be enhanced effectively by adding aluminium oxide in molten fluorides, the electrolytic time can be shortened to 3 h with other conditions unchanged.
By using NH4VO3 as raw material, high-active V2O3 cathode pellets were prepared by reduction with coal gas and in-situ sintering, then were directly reduced to metallic vanadium by rapid electro-deoxidization in molten fluorides. The mechanism of V2O3 electro-deoxidization was studied by cyclic voltammetry experiments and constant potential electrolysis experiments. The results indicate that the rapid electro-deoxidization of V2O3 can be realized in molten fluorides, metallic vanadium containing 0.218 wt% oxygen can be obtained after 4 h electrolysis. The in-suit formation of aluminium-oxygen-fluorine complex ions, which further forming aluminum metal in deoxidation reaction zone, caused aluminum thermal reduction reaction of V2O3 cathode. So direct electro-deoxidation reduction and aluminum thermal reaction of V2O3 both existed in the deoxidation process of V2O3 cathode, and the latter reaction played a key role in acceleration action. Electro-deoxidization process of V2O3 cathode can be enhanced effectively by adding aluminium oxide in molten fluorides, the electrolytic time can be shortened to 3 h with other conditions unchanged.
2018, 47(6):1830-1835.
Abstract:
The Ni35 powder with different mass fraction (the contents are 0%, 25%, 50%, 75% and 100% respectively) of high carbon ferrochrome powder was prepared on the surface of 27SiMn steel using laser cladding technology. The microstructure and the phase of the laser cladding layers were studied by the means of OM, SEM, EDS and XRD. Using micro-hardness tester, abrasive wear machine and electrochemical corrosion tester, the mechanical and corrosion properties of the laser cladding layers were studied. The experimental results show that: the phases of the cladding layers without high carbon ferrochrome are γ-Ni、FeNi3 and Cr2Ni3. When the content is 50%, the α-Cr and (Cr, Fe)7C3 are produced while the Cr2Ni3 disappears. With increasing the content of high carbon ferrochrome, the lath microstructures increase and coarsen constantly. When the content is 50%, Cr element enrichment happens in the petal-looking microstructure of the upper cladding layer and the lath microstructure of the middle cladding layer, and the light gray microstructure is γ-Ni. And with the content increasing, the micro-hardness increase while the wear rate reduce. When the content is 25%, the maximum dilution rate is 20.80% and when the content is 50%, the cladding layers have the best corrosion resistance, and the corrosion current density is the least, which is 0.39 μA/cm2.
The Ni35 powder with different mass fraction (the contents are 0%, 25%, 50%, 75% and 100% respectively) of high carbon ferrochrome powder was prepared on the surface of 27SiMn steel using laser cladding technology. The microstructure and the phase of the laser cladding layers were studied by the means of OM, SEM, EDS and XRD. Using micro-hardness tester, abrasive wear machine and electrochemical corrosion tester, the mechanical and corrosion properties of the laser cladding layers were studied. The experimental results show that: the phases of the cladding layers without high carbon ferrochrome are γ-Ni、FeNi3 and Cr2Ni3. When the content is 50%, the α-Cr and (Cr, Fe)7C3 are produced while the Cr2Ni3 disappears. With increasing the content of high carbon ferrochrome, the lath microstructures increase and coarsen constantly. When the content is 50%, Cr element enrichment happens in the petal-looking microstructure of the upper cladding layer and the lath microstructure of the middle cladding layer, and the light gray microstructure is γ-Ni. And with the content increasing, the micro-hardness increase while the wear rate reduce. When the content is 25%, the maximum dilution rate is 20.80% and when the content is 50%, the cladding layers have the best corrosion resistance, and the corrosion current density is the least, which is 0.39 μA/cm2.
2018, 47(6):1836-1841.
Abstract:
The different of Ag-4Pd and Ag-4Pd-0.5Ru alloy bonding wire properties and structure were analyzed by scanning electron microscope, strength tester and thermal conductivity tester, the effects of Ru on Ag-4Pd alloy bonding wire ball size, bonded micro phonology and bonded strength were investigated. The results show that the thermal conductivity of Ag-4Pd alloy bonding wire decreases from 403 W/m?k to 385 W/m?k because of doping Ru, and the free air ball shape of Ag-4Pd-0.5Ru alloy bonding is more uniform than Ag-4Pd alloy bonding wire, the Ag-4Pd-0.5Ru alloy bonding wire bonded strength is higher than AgA1 alloy bonding wire. The heat affect zone length decreases from 50μm to 35μm because of doping Ru, and the ball neck crack defect cause of excessive long heat affect zone length will decrease. For Ag-4Pd alloy bonding wire, Ru can refine the grain, then the grain size decreases, and the grain quantity increases, then the inhomogeneous deformation of different grain decrease, and the ball bonded shape is uniform.
The different of Ag-4Pd and Ag-4Pd-0.5Ru alloy bonding wire properties and structure were analyzed by scanning electron microscope, strength tester and thermal conductivity tester, the effects of Ru on Ag-4Pd alloy bonding wire ball size, bonded micro phonology and bonded strength were investigated. The results show that the thermal conductivity of Ag-4Pd alloy bonding wire decreases from 403 W/m?k to 385 W/m?k because of doping Ru, and the free air ball shape of Ag-4Pd-0.5Ru alloy bonding is more uniform than Ag-4Pd alloy bonding wire, the Ag-4Pd-0.5Ru alloy bonding wire bonded strength is higher than AgA1 alloy bonding wire. The heat affect zone length decreases from 50μm to 35μm because of doping Ru, and the ball neck crack defect cause of excessive long heat affect zone length will decrease. For Ag-4Pd alloy bonding wire, Ru can refine the grain, then the grain size decreases, and the grain quantity increases, then the inhomogeneous deformation of different grain decrease, and the ball bonded shape is uniform.
2018, 47(6):1842-1847.
Abstract:
The effect of ultrasonic vibration temperature on the microstructure, morphology of eutectic phase and mechanical properties of vacuum counter-pressure casting aluminum alloy were investigated using OM, SEM and electronic universal tester. The results show that the effect of ultrasonic vibration temperature on the microstructure and mechanical properties of aluminum alloy is significantly affected under synergistic action between ultrasonic vibration and vacuum counter-pressure. The microstructure of the primary phase is obviously refined with the increase of the ultrasonic vibration temperature, the optimum ultrasonic vibration temperature is 720℃, the primary phase of the alloy is changed from the part of the dendrite or rosette crystals into fine equiaxed grains, the morphology of eutectic silicon can be changed from thick needle-plate like to fibrous. Meanwhile, the tensile strength and elongation of aluminum alloy reach the maximum value, which are 326.96Mpa and 5.57% respectively. the tensile strength and elongation of aluminum alloy with compound treatment compared with the aluminum alloy in ultrasonic gravity casting increase by up to 14.49%and 22.15% respectively and they are increase by up to 6.33% and 8.16% respectively compared with vacuum counter-pressure casting aluminum alloy.
The effect of ultrasonic vibration temperature on the microstructure, morphology of eutectic phase and mechanical properties of vacuum counter-pressure casting aluminum alloy were investigated using OM, SEM and electronic universal tester. The results show that the effect of ultrasonic vibration temperature on the microstructure and mechanical properties of aluminum alloy is significantly affected under synergistic action between ultrasonic vibration and vacuum counter-pressure. The microstructure of the primary phase is obviously refined with the increase of the ultrasonic vibration temperature, the optimum ultrasonic vibration temperature is 720℃, the primary phase of the alloy is changed from the part of the dendrite or rosette crystals into fine equiaxed grains, the morphology of eutectic silicon can be changed from thick needle-plate like to fibrous. Meanwhile, the tensile strength and elongation of aluminum alloy reach the maximum value, which are 326.96Mpa and 5.57% respectively. the tensile strength and elongation of aluminum alloy with compound treatment compared with the aluminum alloy in ultrasonic gravity casting increase by up to 14.49%and 22.15% respectively and they are increase by up to 6.33% and 8.16% respectively compared with vacuum counter-pressure casting aluminum alloy.
2018, 47(6):1848-1853.
Abstract:
With the addition of SiC particle and copper-mould spray casting, the heterogeneous nucleation ability of AZ91 magnesium alloy is enhanced under high cooing condition and thus the grain refinement of sub-rapid solidified microstructure was fabricated. Then, the effect of annealing temperature (320℃、370℃ and 400℃) on the dynamic solid solution process of divorce eutectic β-Mg17Al12 phase was investigated. As for the spray casted AZ91+1wt%SiC after annealing for 320℃+2h, incomplete solid solution occurs, accompanied by the preservation of initial irregular petal-like morphology and the formation of tiny fringes. After annealing at 370℃, the disappearing rate of β phase is accelerated except for the residual of few grain boundary region. With further increasing temperature to 400℃, a single solid solution of α-Mg phase forms and its morphology transits into fine polygonal grain. Grain refinement is more obvious after the addition of 2wt%SiC, which promotes the process of solid solution due to the shortened atomic diffusion distance. The hardness of copper-mould spray casted magnesium alloy is enhanced by 28.75% due to the addition of SiC and increase of grain refinement, whereas a decline trend appears after solid solution treatment because of the reduction of grain boundary.
With the addition of SiC particle and copper-mould spray casting, the heterogeneous nucleation ability of AZ91 magnesium alloy is enhanced under high cooing condition and thus the grain refinement of sub-rapid solidified microstructure was fabricated. Then, the effect of annealing temperature (320℃、370℃ and 400℃) on the dynamic solid solution process of divorce eutectic β-Mg17Al12 phase was investigated. As for the spray casted AZ91+1wt%SiC after annealing for 320℃+2h, incomplete solid solution occurs, accompanied by the preservation of initial irregular petal-like morphology and the formation of tiny fringes. After annealing at 370℃, the disappearing rate of β phase is accelerated except for the residual of few grain boundary region. With further increasing temperature to 400℃, a single solid solution of α-Mg phase forms and its morphology transits into fine polygonal grain. Grain refinement is more obvious after the addition of 2wt%SiC, which promotes the process of solid solution due to the shortened atomic diffusion distance. The hardness of copper-mould spray casted magnesium alloy is enhanced by 28.75% due to the addition of SiC and increase of grain refinement, whereas a decline trend appears after solid solution treatment because of the reduction of grain boundary.
2018, 47(6):1854-1859.
Abstract:
There are several varieties of tin-based Babbitt in common, among which the mass proportion of Cu element in SnSb11Cu6 is around 6%. The effect of increasing Cu content on mechanical performance of tin-based Babbitt is investigated in this paper. Several new Babbitt samples are remolded by adding Cu powder into molten SnSb11Cu6 Babbitt, and the mass proportions of Cu in the four new samples are 7%, 8%, 9% and 10%. Metallographic analysis, high-temperature compression experiment, friction-wear test and high temperature hardness test are conducted to study the performance of new samples and determine a Cu content to realize the optimal performance. The research results indicate that: 1) the influence of increasing Cu content on metallographic structure is quite significant. Hard Cu6Sn5 phase would increase and α Solid Solution (Sn) would decrease. The proportion of β phase (SnSb) doesn’t change a lot and the grain size enlarges slightly. 2) With the increasing of Cu adding content, compressive yield strength increase at first, and then decreases. When the adding content of Cu powder is around 1%~2%, maximum compressive force and compressive yield strength are larger. 3) The increasing of Cu content doesn’t make an obvious change in friction coefficient of Babbitt alloy. However, anti-wear performance under dry friction is weakened. 4) The softening temperature and hardness under high temperature (90℃) are enhanced by increasing the mass proportions of Cu to around 7%~8%. As the compressive yield strength and the friction-wear performances are not obviously decreased, So the conclusion is that this tin-based Babbitt alloy with the 7%~8% mass proportions of Cu can be used well in sliding bearing, especially in heavy bearing.
There are several varieties of tin-based Babbitt in common, among which the mass proportion of Cu element in SnSb11Cu6 is around 6%. The effect of increasing Cu content on mechanical performance of tin-based Babbitt is investigated in this paper. Several new Babbitt samples are remolded by adding Cu powder into molten SnSb11Cu6 Babbitt, and the mass proportions of Cu in the four new samples are 7%, 8%, 9% and 10%. Metallographic analysis, high-temperature compression experiment, friction-wear test and high temperature hardness test are conducted to study the performance of new samples and determine a Cu content to realize the optimal performance. The research results indicate that: 1) the influence of increasing Cu content on metallographic structure is quite significant. Hard Cu6Sn5 phase would increase and α Solid Solution (Sn) would decrease. The proportion of β phase (SnSb) doesn’t change a lot and the grain size enlarges slightly. 2) With the increasing of Cu adding content, compressive yield strength increase at first, and then decreases. When the adding content of Cu powder is around 1%~2%, maximum compressive force and compressive yield strength are larger. 3) The increasing of Cu content doesn’t make an obvious change in friction coefficient of Babbitt alloy. However, anti-wear performance under dry friction is weakened. 4) The softening temperature and hardness under high temperature (90℃) are enhanced by increasing the mass proportions of Cu to around 7%~8%. As the compressive yield strength and the friction-wear performances are not obviously decreased, So the conclusion is that this tin-based Babbitt alloy with the 7%~8% mass proportions of Cu can be used well in sliding bearing, especially in heavy bearing.
2018, 47(6):1860-1865.
Abstract:
0.1wt.% RE and 0.2~0.8wt.% Ni were added into the Zn20Sn high-temperature lead-free solder. The effects of RE and Ni additions on the microstructure and properties of the solder alloys were investigated. The results show that the solidus temperature of solder alloys is not distinctly affected when the 0.1 wt.% RE and 0.2%~0.8wt.% Ni were added into Zn20Sn solder alloys, whereas the liquidus temperature is decreased, the wettability and microhardness are significantly improved. The solder alloy shows best wettability and highest microhardness when the content of RE is 0.1wt.% and Ni is 0.4wt.%. Ni-containing intermetallic compounds formed in solder alloys and the amount of intermetallic compounds gradually increaseed with increasing Ni content, and the shape of intermetallic compounds and the microstructure of solder alloys are significantly changed.
0.1wt.% RE and 0.2~0.8wt.% Ni were added into the Zn20Sn high-temperature lead-free solder. The effects of RE and Ni additions on the microstructure and properties of the solder alloys were investigated. The results show that the solidus temperature of solder alloys is not distinctly affected when the 0.1 wt.% RE and 0.2%~0.8wt.% Ni were added into Zn20Sn solder alloys, whereas the liquidus temperature is decreased, the wettability and microhardness are significantly improved. The solder alloy shows best wettability and highest microhardness when the content of RE is 0.1wt.% and Ni is 0.4wt.%. Ni-containing intermetallic compounds formed in solder alloys and the amount of intermetallic compounds gradually increaseed with increasing Ni content, and the shape of intermetallic compounds and the microstructure of solder alloys are significantly changed.
2018, 47(6):1866-1871.
Abstract:
In this paper, low surface energy film and a cylindrical micro structure was prepared on titanium alloy by plasma vapor deposition and femtosecond laser technology, the surface morphology of samples were characterized by using scanning electron microscope, the hydrophobicity of samples can be evaluated by using titration angle method, at the same time, the mechanical properties of the film was also tested , the best process was obtained. Finally composting the above two kinds of technologies, the bionic super-hydrophobic surface was prepared on the titanium alloy , the results showed that the surface of titanium alloy with excellent super hydrophobic properties can be obtained by using the composite method of films and microstructures. The water contact angle of the column microstructure with Cu film can reach 156°and its rolling angle can reach 8°.
In this paper, low surface energy film and a cylindrical micro structure was prepared on titanium alloy by plasma vapor deposition and femtosecond laser technology, the surface morphology of samples were characterized by using scanning electron microscope, the hydrophobicity of samples can be evaluated by using titration angle method, at the same time, the mechanical properties of the film was also tested , the best process was obtained. Finally composting the above two kinds of technologies, the bionic super-hydrophobic surface was prepared on the titanium alloy , the results showed that the surface of titanium alloy with excellent super hydrophobic properties can be obtained by using the composite method of films and microstructures. The water contact angle of the column microstructure with Cu film can reach 156°and its rolling angle can reach 8°.
2018, 47(6):1872-1877.
Abstract:
Effect of cooling rete on microstructures, hardness and hydrogen permeation properties of V55Ti30Ni15 alloys were investigated in present study. The results indicate that the microstructures of the alloy consist of the V(Ti, Ni) solid solution and the NiTi and NiTi2 compounds. The cooling rate has significant effects on the microstructures and properties of V55Ti30Ni15 alloys. The volume fraction of V(Ti, Ni) solid solution and second dendrite arm width and spacing decrease with increasing in cooling rate. The hardness value increases with increasing cooling rate, but hydrogen permeability decreases. The hydrogen permeability of V55Ti30Ni15 alloy is linear relationship with the volume fraction of V(Ti, Ni) solid solution. The hydrogen permeability is not only relate to the volume fraction of V(Ti, Ni) solid solution but also the content of Ti and Ni and the volume of phase boundaries in V55Ti30Ni15 alloy.
Effect of cooling rete on microstructures, hardness and hydrogen permeation properties of V55Ti30Ni15 alloys were investigated in present study. The results indicate that the microstructures of the alloy consist of the V(Ti, Ni) solid solution and the NiTi and NiTi2 compounds. The cooling rate has significant effects on the microstructures and properties of V55Ti30Ni15 alloys. The volume fraction of V(Ti, Ni) solid solution and second dendrite arm width and spacing decrease with increasing in cooling rate. The hardness value increases with increasing cooling rate, but hydrogen permeability decreases. The hydrogen permeability of V55Ti30Ni15 alloy is linear relationship with the volume fraction of V(Ti, Ni) solid solution. The hydrogen permeability is not only relate to the volume fraction of V(Ti, Ni) solid solution but also the content of Ti and Ni and the volume of phase boundaries in V55Ti30Ni15 alloy.
2018, 47(6):1878-1883.
Abstract:
Directional solidification process of industrial gas turbine blades (IGTs) was studied based on temperature field and the microstructure was investigated by both simulation and experimental methods. Mathematical model of nonuniform meshes was built to compute temperature field, which improved the computation efficiency effectively. The evolvement rule of mushy zone was analyzed based on simulation results of temperature field. Interpolation algorithm and cellular automaton finite difference (CAFD) model were used to predict the microstructure growth of IGTs. Pouring experiments were carried out, and experiment results agree well with simulation results. Combining with electron backscattered diffraction (EBSD), some common defectsSofScastingsSwereSanalyzed, and theScorresponding preventionSmeasuresSwereSput forward. Primary dendrite arm space (PDAS) and secondary dendrite arm space (SDAS) were calculated considering the influence of solute diffusion and solidification rate, and dendrite morphology was observed by optical microscopy (OM). The results revealed that PDAS and SDAS changed in different transverse section of IGTs. The solidification characteristics of IGTs were studied through macro and micro perspective in order to provide help for industrial production.
Directional solidification process of industrial gas turbine blades (IGTs) was studied based on temperature field and the microstructure was investigated by both simulation and experimental methods. Mathematical model of nonuniform meshes was built to compute temperature field, which improved the computation efficiency effectively. The evolvement rule of mushy zone was analyzed based on simulation results of temperature field. Interpolation algorithm and cellular automaton finite difference (CAFD) model were used to predict the microstructure growth of IGTs. Pouring experiments were carried out, and experiment results agree well with simulation results. Combining with electron backscattered diffraction (EBSD), some common defectsSofScastingsSwereSanalyzed, and theScorresponding preventionSmeasuresSwereSput forward. Primary dendrite arm space (PDAS) and secondary dendrite arm space (SDAS) were calculated considering the influence of solute diffusion and solidification rate, and dendrite morphology was observed by optical microscopy (OM). The results revealed that PDAS and SDAS changed in different transverse section of IGTs. The solidification characteristics of IGTs were studied through macro and micro perspective in order to provide help for industrial production.
2018, 47(6):1884-1889.
Abstract:
In this work, WC-Co and WC-NiCr cermet coatings were deposited by high-efficiency supersonic atmospheric plasma spraying. The erosion resistance of both coatings was comparatively studied in normal or hot corrosion condition. Experimental results suggested that the decarburization happened during the spray of WC-Co or WC-NiCr powders, which led to the formation of W2C. Meanwhile, Co3W3C and Co6W6C were also found in WC-Co coating. Some new phases, such as W3C, W6C2.54, CoWO4 and WO3, were observed in WC-Co coating due to the decomposition and oxidation of WC during hot corrosion. WC-Co coating showed a higher erosion resistance than WC-NiCr coating, however, the erosion resistance of former significantly decreased after hot corrosion. On the contrary, the Cr2O3 that formed during hot corrosion can effectively protect WC from oxidation and thus improve the erosion resistance of WC-NiCr coating.
In this work, WC-Co and WC-NiCr cermet coatings were deposited by high-efficiency supersonic atmospheric plasma spraying. The erosion resistance of both coatings was comparatively studied in normal or hot corrosion condition. Experimental results suggested that the decarburization happened during the spray of WC-Co or WC-NiCr powders, which led to the formation of W2C. Meanwhile, Co3W3C and Co6W6C were also found in WC-Co coating. Some new phases, such as W3C, W6C2.54, CoWO4 and WO3, were observed in WC-Co coating due to the decomposition and oxidation of WC during hot corrosion. WC-Co coating showed a higher erosion resistance than WC-NiCr coating, however, the erosion resistance of former significantly decreased after hot corrosion. On the contrary, the Cr2O3 that formed during hot corrosion can effectively protect WC from oxidation and thus improve the erosion resistance of WC-NiCr coating.
2018, 47(6):1890-1895.
Abstract:
In this paper, Ti-6Al-4V alloy wire was molten by electric arc and then deposited layer by layer for the rapid prototyping of additive manufacture. Morphology, micro-hardness and mechanical properties of Ti-6Al-4V alloy were analyzed. The results indicate that the deposit in the first and the second layers is in the form of columnar crystals and the rest are equiaxial crystals. Meanwhile, a fair amount of heat from arc ensures a good metallurgical bonding in all of zones (deposition zone, fusion zone and deposition zone), and eliminates both clear deposition-layer and martensite of alloy. The integral alloy gets the stable α+β lamellar structural and similar micro-hardness of all zones. Compared with as-cast Ti-6Al-4V alloy, titanium alloy in this work obtains finer initial β-Ti grain and shorter α+β lamellar spacing by Wire+Arc Additive Manufactured. The ultimate strength and elongation of Ti-6Al-4V alloy have increased by 3.6% and 37%, respectively. Besides the tensile fracture morphology of Wire+Arc Additive Manufactured alloy is ductile dimple clearly different from that of as-cast alloy tearing edged quasi-cleavage.
In this paper, Ti-6Al-4V alloy wire was molten by electric arc and then deposited layer by layer for the rapid prototyping of additive manufacture. Morphology, micro-hardness and mechanical properties of Ti-6Al-4V alloy were analyzed. The results indicate that the deposit in the first and the second layers is in the form of columnar crystals and the rest are equiaxial crystals. Meanwhile, a fair amount of heat from arc ensures a good metallurgical bonding in all of zones (deposition zone, fusion zone and deposition zone), and eliminates both clear deposition-layer and martensite of alloy. The integral alloy gets the stable α+β lamellar structural and similar micro-hardness of all zones. Compared with as-cast Ti-6Al-4V alloy, titanium alloy in this work obtains finer initial β-Ti grain and shorter α+β lamellar spacing by Wire+Arc Additive Manufactured. The ultimate strength and elongation of Ti-6Al-4V alloy have increased by 3.6% and 37%, respectively. Besides the tensile fracture morphology of Wire+Arc Additive Manufactured alloy is ductile dimple clearly different from that of as-cast alloy tearing edged quasi-cleavage.
2018, 47(6):1896-1900.
Abstract:
Inner conductor in Niobium superconducting cavity requires a smooth outer surface after material processing, in order to enable the special performance. In the case of downward EBW with full penetration, defects such as underfill and collapse in the face of weld can happen affected by the recoil pressure. In this paper, proper horizontal EBW parameters are used to achieve weld with front reinforcement in accordance with the technical requirements. A 2-D model for the horizontal welding process of 3mm Niobium plate is constructed, and molten pool models with different size and shape are built for different welding parameters. VOF method is applied to simulate the free-surface status of molten pool metal during the welding process, and to obtain the molten pool evolution for different welding parameters. Experiment result indicates the weld width increases with the rise of heat input, and the simulation result matches the experiment.
Inner conductor in Niobium superconducting cavity requires a smooth outer surface after material processing, in order to enable the special performance. In the case of downward EBW with full penetration, defects such as underfill and collapse in the face of weld can happen affected by the recoil pressure. In this paper, proper horizontal EBW parameters are used to achieve weld with front reinforcement in accordance with the technical requirements. A 2-D model for the horizontal welding process of 3mm Niobium plate is constructed, and molten pool models with different size and shape are built for different welding parameters. VOF method is applied to simulate the free-surface status of molten pool metal during the welding process, and to obtain the molten pool evolution for different welding parameters. Experiment result indicates the weld width increases with the rise of heat input, and the simulation result matches the experiment.
2018, 47(6):1901-1905.
Abstract:
Commercially pure aluminum (1060 Al alloy) was subject to a novel process named Equal channel angular expansion extrusion with spherical cavity (ECAEE-SC) for 1 pass at room temperature. The microstructure development of pure aluminum during processing was investigated using optical microscopy (OM) and electron backscattered diffractometry (EBSD). In addition, the microhardness measurements and tensile tests were conducted for mechanical testing. The results show that the ECAEE-SC process is capable of combined severe plastic deformation and shows high extrusion efficiency, the billet has successfully achieved continuous deformation in a single pass. After 1 pass of ECAEE-SC process, the grains were significantly broken and refined under the combined action of mechanical shear, strain accumulation and hydrostatic pressure. A large number of fine homogeneous equiaxed subgrains were formed. The average grain size was 4.6 μm. Also, the extruded materials showed excellent comprehensive mechanical properties. The microhardness was increased from 36.6 HV to 70.2 HV with uniform distribution, more than 91.8% improvement over the as-cast condition. The tensile strength was up to 183.8 MPa, while the elongation decreased to 12.7%. The tensile fracture morphology exhibited remarkable ductile fracture characteristics.
Commercially pure aluminum (1060 Al alloy) was subject to a novel process named Equal channel angular expansion extrusion with spherical cavity (ECAEE-SC) for 1 pass at room temperature. The microstructure development of pure aluminum during processing was investigated using optical microscopy (OM) and electron backscattered diffractometry (EBSD). In addition, the microhardness measurements and tensile tests were conducted for mechanical testing. The results show that the ECAEE-SC process is capable of combined severe plastic deformation and shows high extrusion efficiency, the billet has successfully achieved continuous deformation in a single pass. After 1 pass of ECAEE-SC process, the grains were significantly broken and refined under the combined action of mechanical shear, strain accumulation and hydrostatic pressure. A large number of fine homogeneous equiaxed subgrains were formed. The average grain size was 4.6 μm. Also, the extruded materials showed excellent comprehensive mechanical properties. The microhardness was increased from 36.6 HV to 70.2 HV with uniform distribution, more than 91.8% improvement over the as-cast condition. The tensile strength was up to 183.8 MPa, while the elongation decreased to 12.7%. The tensile fracture morphology exhibited remarkable ductile fracture characteristics.
42 Effect of Pulse Current on Microstructure and Tensile Deformation Behaviorof AZ31 Magnesium Alloy
2018, 47(6):1906-1910.
Abstract:
In order to improve the plastic deformation capacity of magnesium alloy, tensile tests of AZ31 magnesium alloy accompanied with high intensity pulse current were carried out. The effects of pulse current on microstructure and tensile deformation behavior of the alloy were investigated and the mechanisms were examined as well. The results show that the deformation resistance of AZ31 magnesium alloy with pulse current greatly decreases compared with that without pulse current, and the extent of decline raises as current density increases. The dynamic recrystallization (DRX) occurs in the alloy with pulse current during the tensile testing, and obtain fine recrystallized structure, which can bring down the deformation resistance. The rapid recrystallization behavior is based on the enhancement of atomic diffusion and acceleration of the grain boundary transformation from small angle to large angle resulting from pulse current. On the other hand, the increasing of the plastic deforming ability of the alloy was attributed to the electric effect of the pulse current, which can change the activation energy of dislocations and promote the mobility of dislocations.
In order to improve the plastic deformation capacity of magnesium alloy, tensile tests of AZ31 magnesium alloy accompanied with high intensity pulse current were carried out. The effects of pulse current on microstructure and tensile deformation behavior of the alloy were investigated and the mechanisms were examined as well. The results show that the deformation resistance of AZ31 magnesium alloy with pulse current greatly decreases compared with that without pulse current, and the extent of decline raises as current density increases. The dynamic recrystallization (DRX) occurs in the alloy with pulse current during the tensile testing, and obtain fine recrystallized structure, which can bring down the deformation resistance. The rapid recrystallization behavior is based on the enhancement of atomic diffusion and acceleration of the grain boundary transformation from small angle to large angle resulting from pulse current. On the other hand, the increasing of the plastic deforming ability of the alloy was attributed to the electric effect of the pulse current, which can change the activation energy of dislocations and promote the mobility of dislocations.
2018, 47(6):1911-1915.
Abstract:
In order to improve the electrochemical properties of hydrogen storage alloys Mg2Ni, the modified alloy Mg1.8 Zr0.2Ni and MgTi3 was prepared respectively by mechanical alloying (Mechanical Alloying, MA). Then the amorphous modified alloy Mg1.8Zr0.2Ni- (1.2-x) Ni -xMgTi3 was prepared by ball milling a certain percentage Mg1.8 Zr0.2Ni, MgTi3 and Ni. The results show that the composite hydrogen storage alloys after partially replace modified and coating modified have a large number of nanoscale folds, layered voids and multiphase structural defects in their the surface and the interior. With the increase of MgTi3 content, the initial discharge specific capacity of Mg1.8Zr0.2Ni- (1.2-x) Ni -xMgTi3 is also gradually increased. When the content of MgTi3 was x=0.5, the initial discharge specific capacity was 973.3 mAh.g-1. But when the content of MgTi3 was more than x=0.5, the initial discharge specific capacity decreased rapidly. The study shows that the addition of MgTi3 is not beneficial to the cycle stability and high rate discharge performance of the composite hydrogen storage alloys. By tested to the linear polarization,anodic polarization and exchange impedance of Mg1.8Zr0.2Ni- (1.2-x) Ni -xMgTi3, the electrochemical reaction of surface, charge transfer process, the hydrogen diffusion in the alloy and the performance of their electrochemical kinetics of modified alloys were further researched.
In order to improve the electrochemical properties of hydrogen storage alloys Mg2Ni, the modified alloy Mg1.8 Zr0.2Ni and MgTi3 was prepared respectively by mechanical alloying (Mechanical Alloying, MA). Then the amorphous modified alloy Mg1.8Zr0.2Ni- (1.2-x) Ni -xMgTi3 was prepared by ball milling a certain percentage Mg1.8 Zr0.2Ni, MgTi3 and Ni. The results show that the composite hydrogen storage alloys after partially replace modified and coating modified have a large number of nanoscale folds, layered voids and multiphase structural defects in their the surface and the interior. With the increase of MgTi3 content, the initial discharge specific capacity of Mg1.8Zr0.2Ni- (1.2-x) Ni -xMgTi3 is also gradually increased. When the content of MgTi3 was x=0.5, the initial discharge specific capacity was 973.3 mAh.g-1. But when the content of MgTi3 was more than x=0.5, the initial discharge specific capacity decreased rapidly. The study shows that the addition of MgTi3 is not beneficial to the cycle stability and high rate discharge performance of the composite hydrogen storage alloys. By tested to the linear polarization,anodic polarization and exchange impedance of Mg1.8Zr0.2Ni- (1.2-x) Ni -xMgTi3, the electrochemical reaction of surface, charge transfer process, the hydrogen diffusion in the alloy and the performance of their electrochemical kinetics of modified alloys were further researched.
2018, 47(6):1916-1920.
Abstract:
In order to improve the water vapor barrier property of zirconium film adhered to rigid polyurethane foam plastic, a method of the combination of plasma cycle etching and middle frequency magnetron sputtering technologies is proposed by changing the growth mode of zirconium grains. The grain on the surface of the zirconium film exhibits a trend of non crystallization after plasma cycle etching. A kind of normal columnar crystals is found in the cross sectional morphology for the non-etched sample, but a hybrid of columnar crystal and small groups of spherocrystal is observed for the etched sample. Finally, the water vapor barrier properties of zirconium film can be improved by the ion source cyclic etching. The normal columnar crystal growth of the zirconium film is inhibited by the cyclic etching, making the grain more refined, and the film shows a trend of non crystallization, which is regarded as the fundamental reason for the increase of compactness and improvement of water vapor barrier property.
In order to improve the water vapor barrier property of zirconium film adhered to rigid polyurethane foam plastic, a method of the combination of plasma cycle etching and middle frequency magnetron sputtering technologies is proposed by changing the growth mode of zirconium grains. The grain on the surface of the zirconium film exhibits a trend of non crystallization after plasma cycle etching. A kind of normal columnar crystals is found in the cross sectional morphology for the non-etched sample, but a hybrid of columnar crystal and small groups of spherocrystal is observed for the etched sample. Finally, the water vapor barrier properties of zirconium film can be improved by the ion source cyclic etching. The normal columnar crystal growth of the zirconium film is inhibited by the cyclic etching, making the grain more refined, and the film shows a trend of non crystallization, which is regarded as the fundamental reason for the increase of compactness and improvement of water vapor barrier property.
2018, 47(6):1921-1925.
Abstract:
The high permeability Mn-Zn ferrites doped CaO-Bi2O3-MoO3-xNb2O5(x= 0.000- 0.075wt%,step：0.015) were prepared by high temperature solid state reactions. The phase composition, microstructure and electrical and magnetic properties were measured by XRD, SEM, FPP, impedance analyzer and soft magnetic AC testing system. The effects of Nb2O5on the Microstructure and magnetic properties of Mn-Zn ferrites were investigated. The results showed that Nb2O5 can refine the microstructure, improve the density, frequency stability and quality factor, electrical resistivity and reduce specific losses when a small amount of doping Nb2O5 are added. Nb2O5 would result in the deterioration of microstructure and the electromagnetic properties of the Mn-Zn ferrites when a large amount of doping Nb2O5 is added. When the Nb2O5 doping amount is 0.030wt%, the best comprehensive performance of Mn-Zn ferrites were obtained.
The high permeability Mn-Zn ferrites doped CaO-Bi2O3-MoO3-xNb2O5(x= 0.000- 0.075wt%,step：0.015) were prepared by high temperature solid state reactions. The phase composition, microstructure and electrical and magnetic properties were measured by XRD, SEM, FPP, impedance analyzer and soft magnetic AC testing system. The effects of Nb2O5on the Microstructure and magnetic properties of Mn-Zn ferrites were investigated. The results showed that Nb2O5 can refine the microstructure, improve the density, frequency stability and quality factor, electrical resistivity and reduce specific losses when a small amount of doping Nb2O5 are added. Nb2O5 would result in the deterioration of microstructure and the electromagnetic properties of the Mn-Zn ferrites when a large amount of doping Nb2O5 is added. When the Nb2O5 doping amount is 0.030wt%, the best comprehensive performance of Mn-Zn ferrites were obtained.
2018, 47(6):1926-1930.
Abstract:
In this study, the numerical simulation of rolling process and experimental verification was carried out at 400℃ temperature of as-cast the AZ31 magnesium alloy sheet with initial thickness of 7mm. The reduction was 10%, 15%, 20%, 25%, 30%, 35%, 40% and 45%, respectively. Microstructure and edge crack were analyzed after rolling. The results show that the edge crack was occurred when the single pass reduction up to 20%. The edge crack depth has increased from 5.04mm of 20% reduction to 14.05mm of 45% in current rolling condition. According to numerical simulation results, the damage distribution along the width of the plate was obtained. And we have established the prediction model of edge crack depth. For the edge crack depth, the average error between the actual measured data and the calculated value by the prediction model is 9.23%. The SEM observation results show that the microstructure near the edge crack contain a large number of twins.
In this study, the numerical simulation of rolling process and experimental verification was carried out at 400℃ temperature of as-cast the AZ31 magnesium alloy sheet with initial thickness of 7mm. The reduction was 10%, 15%, 20%, 25%, 30%, 35%, 40% and 45%, respectively. Microstructure and edge crack were analyzed after rolling. The results show that the edge crack was occurred when the single pass reduction up to 20%. The edge crack depth has increased from 5.04mm of 20% reduction to 14.05mm of 45% in current rolling condition. According to numerical simulation results, the damage distribution along the width of the plate was obtained. And we have established the prediction model of edge crack depth. For the edge crack depth, the average error between the actual measured data and the calculated value by the prediction model is 9.23%. The SEM observation results show that the microstructure near the edge crack contain a large number of twins.
2018, 47(6):1931-1935.
Abstract:
By introducing (WO3+Al) thermites into the (Ti+B4C) combustion system and adjusting the proportion of two systems, TiB2-TiC-(Ti, W)Ccomposite ceramics with different W mass fraction were prepared by SHS centrifugal casting. XRD, FESEM and EDS results show that the ceramic matrix is mainly composed of TiB2, TiC and (Ti, W)C. As W content increases, volume fraction of (Ti, W)C increases, and volume fraction of TiB2 and TiC decrease. Meanwhile, the grains are fined and distributed uniformly. Mechanical properties tests show that relative density and Vickers hardness of the ceramics are on the rise as W content increases, while, flexural strength and fracture toughness of the ceramics firstly increase and then decrease, and achieve maximum when W content is 65%. This is due to the decrease in volume fraction of TiB2 platelet which is the only reinforced phase of the TiB2-TiC-(Ti, W)Ccomposite ceramic.
By introducing (WO3+Al) thermites into the (Ti+B4C) combustion system and adjusting the proportion of two systems, TiB2-TiC-(Ti, W)Ccomposite ceramics with different W mass fraction were prepared by SHS centrifugal casting. XRD, FESEM and EDS results show that the ceramic matrix is mainly composed of TiB2, TiC and (Ti, W)C. As W content increases, volume fraction of (Ti, W)C increases, and volume fraction of TiB2 and TiC decrease. Meanwhile, the grains are fined and distributed uniformly. Mechanical properties tests show that relative density and Vickers hardness of the ceramics are on the rise as W content increases, while, flexural strength and fracture toughness of the ceramics firstly increase and then decrease, and achieve maximum when W content is 65%. This is due to the decrease in volume fraction of TiB2 platelet which is the only reinforced phase of the TiB2-TiC-(Ti, W)Ccomposite ceramic.
2018, 47(6):1936-1940.
Abstract:
Vacuum brazing of TZM alloy and ZrCp-W composite was achieved by using Ti-50Ni (at. %) eutectic brazing alloy. The typical interfacial microstructure of brazed joints was TZM/Ti-Mo+TiNi3+Mo-Ti-W/TiNi+TiNi3+W(s,s)+TiC/ZrCp-W, which was characterized using SEM, EDS and XRD. In addition, the effect of brazing temperature on interfacial microstructure and joining properties of TZM/Ti-50Ni/ZrCp-W brazed joints was investigated in detail. As the brazing temperature increased, more and more elements Ti and Ni in molten brazing alloy diffused into the base materials, which in turn broaden the brazed joints. At the same time, the grain size gradually increased and the grain boundary became smoother. Experimental results demonstrated that reliable brazed joints with average shear strength up to 146 MPa was achieved when brazed at 1340 °C for 10 min.
Vacuum brazing of TZM alloy and ZrCp-W composite was achieved by using Ti-50Ni (at. %) eutectic brazing alloy. The typical interfacial microstructure of brazed joints was TZM/Ti-Mo+TiNi3+Mo-Ti-W/TiNi+TiNi3+W(s,s)+TiC/ZrCp-W, which was characterized using SEM, EDS and XRD. In addition, the effect of brazing temperature on interfacial microstructure and joining properties of TZM/Ti-50Ni/ZrCp-W brazed joints was investigated in detail. As the brazing temperature increased, more and more elements Ti and Ni in molten brazing alloy diffused into the base materials, which in turn broaden the brazed joints. At the same time, the grain size gradually increased and the grain boundary became smoother. Experimental results demonstrated that reliable brazed joints with average shear strength up to 146 MPa was achieved when brazed at 1340 °C for 10 min.
2018, 47(6):1941-1944.
Abstract:
Effect of solution and aging heat treatment with lower temperature on the microstructures and mechanical properties of TC4 alloy bars were studied in this paper. Different heat treatment schedules were adopted and compared on titanium bars with fully equiaxed microstructure. The results show that with 700℃ solution temperature, strength of TC4 alloy decreases. Compared with the as forged alloy, rupture strength of the alloy reduce 77 MPa after solution treatment at 700℃. Aging at temperatures lower than 650℃ has great influence on the mechanical of TC4 alloy, aging at 400℃ could get ideal match of strength and plasticity.
Effect of solution and aging heat treatment with lower temperature on the microstructures and mechanical properties of TC4 alloy bars were studied in this paper. Different heat treatment schedules were adopted and compared on titanium bars with fully equiaxed microstructure. The results show that with 700℃ solution temperature, strength of TC4 alloy decreases. Compared with the as forged alloy, rupture strength of the alloy reduce 77 MPa after solution treatment at 700℃. Aging at temperatures lower than 650℃ has great influence on the mechanical of TC4 alloy, aging at 400℃ could get ideal match of strength and plasticity.
2018, 47(6):1945-1950.
Abstract:
Tungsten is one of the most important candidate materials in plasma surface materials, due to its excellent physical and chemical properties. On the basis of comparison and analysis of damage behavior of pure tungsten and tungsten-base materials under high heat load, such as rolled tungsten, recrystallization tungsten, W-La2O3、W-TiC、W-ZrC、W-V and W-Ta. Damage mechanism are discussed. Several key issues which need to be studied hereafter are put forward.
Tungsten is one of the most important candidate materials in plasma surface materials, due to its excellent physical and chemical properties. On the basis of comparison and analysis of damage behavior of pure tungsten and tungsten-base materials under high heat load, such as rolled tungsten, recrystallization tungsten, W-La2O3、W-TiC、W-ZrC、W-V and W-Ta. Damage mechanism are discussed. Several key issues which need to be studied hereafter are put forward.
