Volume 49,Issue 9,2020 Table of Contents
2020, 49(9):2913-2919.
DOI: 10.12442/j.issn.1002-185X.E20190090
Abstract:
Ti6Al4V single beads were prepared by electron beam freeform fabrication (EBF3) to investigate their geometry, microstructure, composition and the resulting hardness in terms of the wire-feed rate, beam power and travel speed. Results showed that an increased wire-feed rate favored to increase the deposition efficiency and geometry accuracy, but it required an affordable heat input to success in deposition. The narrowed columnar β grains filled with the fine microstructural features inside and the decreased Al evaporation loss were available at an increased wire-feed rate/travel speed or a decreased beam power, which was attributed to the decreased temperature and dimension of molten pool. Therefore, the beads produced at such process variables possess the increased hardness. This investigation reveals the correlation between the process parameters and the process outcomes of deposited beads, which offers a valuable guidance for accurate manufacturing of multi-layered components with reliable microstructure and mechanical properties.
Ti6Al4V single beads were prepared by electron beam freeform fabrication (EBF3) to investigate their geometry, microstructure, composition and the resulting hardness in terms of the wire-feed rate, beam power and travel speed. Results showed that an increased wire-feed rate favored to increase the deposition efficiency and geometry accuracy, but it required an affordable heat input to success in deposition. The narrowed columnar β grains filled with the fine microstructural features inside and the decreased Al evaporation loss were available at an increased wire-feed rate/travel speed or a decreased beam power, which was attributed to the decreased temperature and dimension of molten pool. Therefore, the beads produced at such process variables possess the increased hardness. This investigation reveals the correlation between the process parameters and the process outcomes of deposited beads, which offers a valuable guidance for accurate manufacturing of multi-layered components with reliable microstructure and mechanical properties.
2020, 49(9):2920-2924.
DOI: 10.12442/j.issn.1002-185X.20190542
Abstract:
The microstructures and mechanical properties of as-extruded and peak-aged Mg-6Zn-1Mn-2Sn-0.5Ca(ZMT612-0.5Ca) alloy were studied using optical microscopy (OM), X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), hardness tests and uniaxial tensile tests. The results showed that the as-cast alloy consisted of α-Mg, Mn, Mg7Zn3, Ca2Mg6Zn3 and CaMgSn phases. The as-extruded ZMT612-0.5Ca alloy presented a totally recrystallized microstructure. The average grain size of extruded alloy was ~2.8 μm. After heat treatment, the strength increased obviously, the yield strength and ultimate tensile strength of as-extruded alloy were increased to 320 and 390 MPa, respectively. Strength enhancement was attributed to the grain boundary strengthening, solid solution strengthening and precipitation strengthening.
The microstructures and mechanical properties of as-extruded and peak-aged Mg-6Zn-1Mn-2Sn-0.5Ca(ZMT612-0.5Ca) alloy were studied using optical microscopy (OM), X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), hardness tests and uniaxial tensile tests. The results showed that the as-cast alloy consisted of α-Mg, Mn, Mg7Zn3, Ca2Mg6Zn3 and CaMgSn phases. The as-extruded ZMT612-0.5Ca alloy presented a totally recrystallized microstructure. The average grain size of extruded alloy was ~2.8 μm. After heat treatment, the strength increased obviously, the yield strength and ultimate tensile strength of as-extruded alloy were increased to 320 and 390 MPa, respectively. Strength enhancement was attributed to the grain boundary strengthening, solid solution strengthening and precipitation strengthening.
2020, 49(9):2925-2929.
DOI: 10.12442/j.issn.1002-185X.E20190092
Abstract:
High-cycle fatigue (HCF) tests at different temperatures were performed on a single crystal superalloy SRR99 with [001] orientation. The results demonstrate that conditional fatigue strength firstly increases and then decreases with the increase of temperature. It exhibits the same tendency with tensile strength at elevated temperatures. The microstructures are observed by SEM and TEM and it is found that the morphology of g′ particles changes significantly and dissolution of g′ particles takes place during cyclic loading. This is likely induced by the back and forth movement of interface dislocations during the cyclic loading. As a result, the strengthening effect from the coherent g/g′ coherent interfaces is gradually deteriorated during high-cycle fatigue deformation. On the other hand, the fatigue crack propagation is found to be primarily along a specific crystalline plane, which is identified as (111). The specific mechanism for the microstructure evolution during cyclic loading is discussed based on SEM and TEM observations.
High-cycle fatigue (HCF) tests at different temperatures were performed on a single crystal superalloy SRR99 with [001] orientation. The results demonstrate that conditional fatigue strength firstly increases and then decreases with the increase of temperature. It exhibits the same tendency with tensile strength at elevated temperatures. The microstructures are observed by SEM and TEM and it is found that the morphology of g′ particles changes significantly and dissolution of g′ particles takes place during cyclic loading. This is likely induced by the back and forth movement of interface dislocations during the cyclic loading. As a result, the strengthening effect from the coherent g/g′ coherent interfaces is gradually deteriorated during high-cycle fatigue deformation. On the other hand, the fatigue crack propagation is found to be primarily along a specific crystalline plane, which is identified as (111). The specific mechanism for the microstructure evolution during cyclic loading is discussed based on SEM and TEM observations.
2020, 49(9):2930-2936.
DOI: 10.12442/j.issn.1002-185X.20190543
Abstract:
Based on the poor plasticity and high temperature required for forming of titanium alloy sheet, an ultrasonic vibration-assisted forming method under thermal conditions was proposed, which is expected to further improve the formability of titanium alloy sheets under thermal conditions. The effects of ultrasonic vibration process parameters on the engineering stress-strain curve, yield strength and elongation of titanium alloy sheet were analyzed by tensile test of TC4 sheet at 200-600℃. And the microstructure and fractography of the tensile specimens were analyzed. The results showed that superimposing ultrasonic vibration process with appropriate parameters in the thermal tensile process can further reduce the flow stress and yield strength of TC4 sheet and improve the elongation, and it can achieve the purpose of further improving the formability under thermal conditions.
Based on the poor plasticity and high temperature required for forming of titanium alloy sheet, an ultrasonic vibration-assisted forming method under thermal conditions was proposed, which is expected to further improve the formability of titanium alloy sheets under thermal conditions. The effects of ultrasonic vibration process parameters on the engineering stress-strain curve, yield strength and elongation of titanium alloy sheet were analyzed by tensile test of TC4 sheet at 200-600℃. And the microstructure and fractography of the tensile specimens were analyzed. The results showed that superimposing ultrasonic vibration process with appropriate parameters in the thermal tensile process can further reduce the flow stress and yield strength of TC4 sheet and improve the elongation, and it can achieve the purpose of further improving the formability under thermal conditions.
2020, 49(9):2937-2947.
DOI: 10.12442/j.issn.1002-185X.20190652
Abstract:
With the increase of operating temperature in aero-engine turbine blades, a vitreousSmaterial (CMAS) consisting mainly of CaO, MgO, Al2O3 and SiO2 were increasingly harmful to the thermal barrier coatings deposited on the blade. Therefore, the performance and durability of thermal barrier coatings should meet higher requirements. In this study, the influence of CMAS penetration on interfacial crack propagation and residual stress in the electron beam physical vapor deposition thermal barrier coatings was investigated by using finite element method. The sinusoidal curves with fixed wavelength and varying amplitude were used to model the interfaces with different roughness. At the same time, the effect of the elastic modulus of CMAS and the interaction between interface morphology and CMAS were taken into account. The results show that the increase of CMAS elastic modulus has an inhibitory effect on interfacial cracks, and the smaller the TGO amplitude and thickness, the more obvious the inhibition. There is a critical point for the effect of CMAS elastic modulus on the maximum residual stress S22 in top coat (TC) layer. Before the critical point, the change of CMAS elastic modulus has a greater influence on the maximum residual stress of TC layer, and with the increase of elastic modulus of CMAS, the maximum residual stress of TC layer decreases greatly; after the critical point, the maximum residual stress of TC layer is hardly affected by the change of elastic modulus of CMAS. These results are of great significance for the study of the failure mechanism of thermal barrier coatings by electron beam physical vapor deposition, it can provide guidance for the optimization of the interface of thermal barrier coatings.
With the increase of operating temperature in aero-engine turbine blades, a vitreousSmaterial (CMAS) consisting mainly of CaO, MgO, Al2O3 and SiO2 were increasingly harmful to the thermal barrier coatings deposited on the blade. Therefore, the performance and durability of thermal barrier coatings should meet higher requirements. In this study, the influence of CMAS penetration on interfacial crack propagation and residual stress in the electron beam physical vapor deposition thermal barrier coatings was investigated by using finite element method. The sinusoidal curves with fixed wavelength and varying amplitude were used to model the interfaces with different roughness. At the same time, the effect of the elastic modulus of CMAS and the interaction between interface morphology and CMAS were taken into account. The results show that the increase of CMAS elastic modulus has an inhibitory effect on interfacial cracks, and the smaller the TGO amplitude and thickness, the more obvious the inhibition. There is a critical point for the effect of CMAS elastic modulus on the maximum residual stress S22 in top coat (TC) layer. Before the critical point, the change of CMAS elastic modulus has a greater influence on the maximum residual stress of TC layer, and with the increase of elastic modulus of CMAS, the maximum residual stress of TC layer decreases greatly; after the critical point, the maximum residual stress of TC layer is hardly affected by the change of elastic modulus of CMAS. These results are of great significance for the study of the failure mechanism of thermal barrier coatings by electron beam physical vapor deposition, it can provide guidance for the optimization of the interface of thermal barrier coatings.
2020, 49(9):2948-2955.
DOI: 10.12442/j.issn.1002-185X.20190560
Abstract:
In order to investigate the relationship between Ce(SO4)2 concentration and surface performance, a series of workpieces coated with Ni-W-Ce alloy was fabricated by Jet-Electrodeposition. The cellular structure was observed by SEM, and the composition of coating elements was analyzed by EDS. XRD analysis showed that the coating had lattice distortion. LEXT4100 laser confocal microscope observed wear mark and found that the friction mechanism was to be changed. The results indicate that the addition of Ce(SO4)2 improved the surface micromorphology of the coating, and the best surface quality occurred when the concentration is 0.5g/L. Meanwhile micro-hardness, wear resistance and corrosion resistance show a rule of first getting better and then getting worse with the concentration increasing. When the concentration of Ce(SO4)2 is 0.5g/L, the micro-hardness reached the peak value of 519.69HV0.1.The wear resistance was the best as the wear resistance mark parameters dropped to the valley value. The corrosion resistance was also the best, which the corrosion potential was -0.5537V and the arc reactance radius of the minimum.
In order to investigate the relationship between Ce(SO4)2 concentration and surface performance, a series of workpieces coated with Ni-W-Ce alloy was fabricated by Jet-Electrodeposition. The cellular structure was observed by SEM, and the composition of coating elements was analyzed by EDS. XRD analysis showed that the coating had lattice distortion. LEXT4100 laser confocal microscope observed wear mark and found that the friction mechanism was to be changed. The results indicate that the addition of Ce(SO4)2 improved the surface micromorphology of the coating, and the best surface quality occurred when the concentration is 0.5g/L. Meanwhile micro-hardness, wear resistance and corrosion resistance show a rule of first getting better and then getting worse with the concentration increasing. When the concentration of Ce(SO4)2 is 0.5g/L, the micro-hardness reached the peak value of 519.69HV0.1.The wear resistance was the best as the wear resistance mark parameters dropped to the valley value. The corrosion resistance was also the best, which the corrosion potential was -0.5537V and the arc reactance radius of the minimum.
2020, 49(9):2956-2965.
DOI: 10.12442/j.issn.1002-185X.20190555
Abstract:
The hot deformation behavior of GH2907 superalloy in deformation temperature of 950℃~1100℃, strain rates of 0.01s-1~10s-1 and deformation degree of 60% was studied by thermal simulation compression experiments. The flow stress decreases significantly as the deformation temperature increases or strain rate decreases; according to the Arrhenius equation and the Zener-Hollomon parameter, the thermal deformation activation energy (Q) can be calculated, and the hot deformation constitutive equation of GH2907 superalloy also is established. On the basis of the dynamic material model, the power dissipation map under different strains of the GH2907 superalloy is obtained. The region with higher power dissipation efficiency (η) is located in the temperature of 1050~1100℃ with strain rates of 0.01~0.03s-1, and the microstructure dynamic recrystallization phenomenon also occurs in the deformation region; based on the Preased instability criterion, the hot processing map of GH2907 superalloy under different strains is drawn. The rheological instability zone is located in the high temperature range of 970~1100℃ and high strain rate range of 0.6~10s-1. In addition, the dynamic recrystallized grains are distributed along the adiabatic shear band and local flow in this deformation region. According to the hot processing map and microstructure analysis of GH2907 superalloy, the suitable processing area is in the temperature of 1050~1100℃ and strain rates of 0.01~0.03s-1.
The hot deformation behavior of GH2907 superalloy in deformation temperature of 950℃~1100℃, strain rates of 0.01s-1~10s-1 and deformation degree of 60% was studied by thermal simulation compression experiments. The flow stress decreases significantly as the deformation temperature increases or strain rate decreases; according to the Arrhenius equation and the Zener-Hollomon parameter, the thermal deformation activation energy (Q) can be calculated, and the hot deformation constitutive equation of GH2907 superalloy also is established. On the basis of the dynamic material model, the power dissipation map under different strains of the GH2907 superalloy is obtained. The region with higher power dissipation efficiency (η) is located in the temperature of 1050~1100℃ with strain rates of 0.01~0.03s-1, and the microstructure dynamic recrystallization phenomenon also occurs in the deformation region; based on the Preased instability criterion, the hot processing map of GH2907 superalloy under different strains is drawn. The rheological instability zone is located in the high temperature range of 970~1100℃ and high strain rate range of 0.6~10s-1. In addition, the dynamic recrystallized grains are distributed along the adiabatic shear band and local flow in this deformation region. According to the hot processing map and microstructure analysis of GH2907 superalloy, the suitable processing area is in the temperature of 1050~1100℃ and strain rates of 0.01~0.03s-1.
2020, 49(9):2966-2972.
DOI: 10.12442/j.issn.1002-185X.20190563
Abstract:
The solidification process and microstructure of ZL201 aluminum alloy auxiliary frame were simulated by Cellular Automation(CA) method, and the temperature field and CAFE(microstructure simulation) field were established. According to the solid and liquid phase lines of ZL201 aluminum alloy, the six different nucleating surfaces were determined. The simulation results of temperature field show that the nucleation rate and growth rate can be controlled in the most suitable range by oil cooling. The nucleation rate is 1/276 s·cm3and growth rate is 65.2μm/s. The calculation results of thermodynamic phase diagram show that in the formation process of Al3Ti phase, which absorbs covalent electrons from surrounding aluminum atoms. With the increasing of titanium content, the precipitation temperature of Al3Ti increases. In addition, the content of Al3Ti has increased from 0.144mol% to 0.698mol%, and the effect of grain refinement became more and more obvious. Through the simulation of the microstructure of ZL201 aluminum alloy auxiliary frame, the corresponding <100> polar diagram and the experimental metallographic structure, it is shown that the change of Ti content has a significant impact on the grain refinement effect of ZL201 aluminum alloy auxiliary frame microstructure. With the increasing of titanium content, the new phase Al3Ti promotes grain refinement and composition uniformity. It can be seen from the simulated polar diagram of <100> that the increase of Ti content is conducive to the preferential orientation of grains, and the grain refinement is achieved by slowing down the competition among grains. The results of simulation are basically consistent with the metallographic structure obtained by experiment.
The solidification process and microstructure of ZL201 aluminum alloy auxiliary frame were simulated by Cellular Automation(CA) method, and the temperature field and CAFE(microstructure simulation) field were established. According to the solid and liquid phase lines of ZL201 aluminum alloy, the six different nucleating surfaces were determined. The simulation results of temperature field show that the nucleation rate and growth rate can be controlled in the most suitable range by oil cooling. The nucleation rate is 1/276 s·cm3and growth rate is 65.2μm/s. The calculation results of thermodynamic phase diagram show that in the formation process of Al3Ti phase, which absorbs covalent electrons from surrounding aluminum atoms. With the increasing of titanium content, the precipitation temperature of Al3Ti increases. In addition, the content of Al3Ti has increased from 0.144mol% to 0.698mol%, and the effect of grain refinement became more and more obvious. Through the simulation of the microstructure of ZL201 aluminum alloy auxiliary frame, the corresponding <100> polar diagram and the experimental metallographic structure, it is shown that the change of Ti content has a significant impact on the grain refinement effect of ZL201 aluminum alloy auxiliary frame microstructure. With the increasing of titanium content, the new phase Al3Ti promotes grain refinement and composition uniformity. It can be seen from the simulated polar diagram of <100> that the increase of Ti content is conducive to the preferential orientation of grains, and the grain refinement is achieved by slowing down the competition among grains. The results of simulation are basically consistent with the metallographic structure obtained by experiment.
2020, 49(9):2973-2977.
DOI: 10.12442/j.issn.1002-185X.20190564
Abstract:
The hot deformation behavior of Mg-5Y-0.5Ce-0.5Zr magnesium alloy was studied by means of hot compression tests at deformation temperatures from 300 oC to 450 oC and strain rates from 0.01 s-1 to 1 s-1. The results showed that the flow stress of the alloy is changed with deformation temperature and strain rate during the hot compression deformation. The flow stress of the alloy decreases with increasing deformation temperature at the same strain rate, and decreases with decreasing strain rate at the same deformation temperature. The constitutive equation for hot compression flow stress of the alloy is established in a hyperbolic-sine form. The hot deformation activation energy Q of the alloy is 253 kJ/mol.
The hot deformation behavior of Mg-5Y-0.5Ce-0.5Zr magnesium alloy was studied by means of hot compression tests at deformation temperatures from 300 oC to 450 oC and strain rates from 0.01 s-1 to 1 s-1. The results showed that the flow stress of the alloy is changed with deformation temperature and strain rate during the hot compression deformation. The flow stress of the alloy decreases with increasing deformation temperature at the same strain rate, and decreases with decreasing strain rate at the same deformation temperature. The constitutive equation for hot compression flow stress of the alloy is established in a hyperbolic-sine form. The hot deformation activation energy Q of the alloy is 253 kJ/mol.
2020, 49(9):2978-2982.
DOI: 10.12442/j.issn.1002-185X.20190594
Abstract:
In the present study, a novel gas multiple-tunnel plasma spraying technology was adopted to fabricate amorphous Fe-based composite coatings with various contents of ZrO2. By this way, the ZrO2 particles were distributed homogeneously in the matrix and the proportion of the two phases in the composite coatings can be regulated. During the wear process, the wear resistance is improved for the composite coatings. Meanwhile, the introduction of ZrO2 improves both the corrosion resistance and porosity. Therefore the best corrosion resistance is obtained for the composite coating with 50% ZrO2.
In the present study, a novel gas multiple-tunnel plasma spraying technology was adopted to fabricate amorphous Fe-based composite coatings with various contents of ZrO2. By this way, the ZrO2 particles were distributed homogeneously in the matrix and the proportion of the two phases in the composite coatings can be regulated. During the wear process, the wear resistance is improved for the composite coatings. Meanwhile, the introduction of ZrO2 improves both the corrosion resistance and porosity. Therefore the best corrosion resistance is obtained for the composite coating with 50% ZrO2.
2020, 49(9):2983-2990.
DOI: 10.12442/j.issn.1002-185X.E20190093
Abstract:
Thermo-Calc software was used to calculate the thermodynamics of nickel-based corrosion resistant Hastelloy G3 alloy, and the influence of composition on the precipitation of equilibrium phase was systematically studied. The precipitated phase of alloy after aging treatment was observed by the SEM and TEM. The results show that the equilibrium phases of alloy precipitation are mainly σ phase, μ phase, M6C and M23C6; the content of Cr and Mo mainly affect the precipitation of σ phase and μ phase and the initial precipitation temperature; while the content of C significantly affects the precipitation behavior of carbides M6C and M23C6; The precipitation rule of precipitates during the aging process is further studied through experiments.
Thermo-Calc software was used to calculate the thermodynamics of nickel-based corrosion resistant Hastelloy G3 alloy, and the influence of composition on the precipitation of equilibrium phase was systematically studied. The precipitated phase of alloy after aging treatment was observed by the SEM and TEM. The results show that the equilibrium phases of alloy precipitation are mainly σ phase, μ phase, M6C and M23C6; the content of Cr and Mo mainly affect the precipitation of σ phase and μ phase and the initial precipitation temperature; while the content of C significantly affects the precipitation behavior of carbides M6C and M23C6; The precipitation rule of precipitates during the aging process is further studied through experiments.
2020, 49(9):2991-2996.
DOI: 10.12442/j.issn.1002-185X.20200093
Abstract:
High power pulsed magnetron sputtering (HPPMS) improves microstructure and mechanical properties of TiN coating by high density plasma using a pulsed high peak target power density (e.g. 1-3 kW/cm2). However, the low average deposition rate increases preparation cost of coating, which becomes a downside of HPPMS technique. A dual-stage HPPMS technique, which has two continuous and independently adjustable steps in one pulse period, is developed in order to solve low deposition rate of traditional HPPMS. Through the reasonable allocation of electric field of dual-stage HPPMS, a fine and dense structure of TiN coating is prepared. The effects of target current of dual-stage HPPMS on the microstructure and corrosion resistance of TiN coating are studied. It was found that the morphology of target surface changed from small pits to large-area craters when target current increased to 20 A. It indicated that the leave-target mode of deposited particles changed from sputtering to sublimation or evaporation. Additionally, when target current was 10 A, the TiN coating exhibited a pyramid shape particles with average grain size of 11 nm. When target current increased to 25 A, the TiN coating showed a circular shape particles with average grain size of 18 nm and dense columnar structure. This microstructure gave rise to a better corrosion resistance.
High power pulsed magnetron sputtering (HPPMS) improves microstructure and mechanical properties of TiN coating by high density plasma using a pulsed high peak target power density (e.g. 1-3 kW/cm2). However, the low average deposition rate increases preparation cost of coating, which becomes a downside of HPPMS technique. A dual-stage HPPMS technique, which has two continuous and independently adjustable steps in one pulse period, is developed in order to solve low deposition rate of traditional HPPMS. Through the reasonable allocation of electric field of dual-stage HPPMS, a fine and dense structure of TiN coating is prepared. The effects of target current of dual-stage HPPMS on the microstructure and corrosion resistance of TiN coating are studied. It was found that the morphology of target surface changed from small pits to large-area craters when target current increased to 20 A. It indicated that the leave-target mode of deposited particles changed from sputtering to sublimation or evaporation. Additionally, when target current was 10 A, the TiN coating exhibited a pyramid shape particles with average grain size of 11 nm. When target current increased to 25 A, the TiN coating showed a circular shape particles with average grain size of 18 nm and dense columnar structure. This microstructure gave rise to a better corrosion resistance.
2020, 49(9):2997-3004.
DOI: 10.12442/j.issn.1002-185X.E20190094
Abstract:
The stress corrosion cracking （SCC） and corrosion fatigue (CF) behaviors of micro-arc oxidized (MAO) Mg-3Al-1Zn alloy were conducted in air and 3.5 wt.% Na2SO4 solution, and their relations were discussed. The corrosion properties of the MAO Mg-3Al-1Zn alloy were improved significantly. Compared with those of the Mg-3Al-1Zn substrate, the SCC and CF strengthes of the MAO Mg-3Al-1Zn alloy were both reduced only about 10 MPa slightly in air. In 3.5 wt.% Na2SO4 solution, the CF properties were still degraded, but the SCC properties of the MAO specimens were enhanced apparently, from 58.24 MPa to 202.08 MPa. It indicated that the mechanical properties (SCC and CF) were not always linearly related with the corrosion resistance of the material. It was ductile fracture for the SCC specimens in air, and it was cleavage fracture in 3.5 wt.% Na2SO4 solution. While they were cleavage fractures for CF specimens regardless of the environments. This was due to the effect of the corrosive environment and alternating cyclic loading, which accelerated the crack propagation process. It displayed that the surrounding environments and loading types could affect the fracture mechanism of the material.
The stress corrosion cracking （SCC） and corrosion fatigue (CF) behaviors of micro-arc oxidized (MAO) Mg-3Al-1Zn alloy were conducted in air and 3.5 wt.% Na2SO4 solution, and their relations were discussed. The corrosion properties of the MAO Mg-3Al-1Zn alloy were improved significantly. Compared with those of the Mg-3Al-1Zn substrate, the SCC and CF strengthes of the MAO Mg-3Al-1Zn alloy were both reduced only about 10 MPa slightly in air. In 3.5 wt.% Na2SO4 solution, the CF properties were still degraded, but the SCC properties of the MAO specimens were enhanced apparently, from 58.24 MPa to 202.08 MPa. It indicated that the mechanical properties (SCC and CF) were not always linearly related with the corrosion resistance of the material. It was ductile fracture for the SCC specimens in air, and it was cleavage fracture in 3.5 wt.% Na2SO4 solution. While they were cleavage fractures for CF specimens regardless of the environments. This was due to the effect of the corrosive environment and alternating cyclic loading, which accelerated the crack propagation process. It displayed that the surrounding environments and loading types could affect the fracture mechanism of the material.
2020, 49(9):3005-3011.
DOI: 10.12442/j.issn.1002-185X.20190615
Abstract:
It is important to understand the microstructural evolution during water quenching after different processing conditions in order to obtain optimum mechanical properties of Ti-6Al-4V alloy. The thermal simulation of Ti-6Al-4V alloy was conducted using a thermomechanical simulator. The results have shown that a fully martensitic microstructure was obtained after solution treatment. Water-quenching after solution resulted in hardness increase, and this was attributed to the presence of α′ and α″. The lamellar structure formed when the specimen was water-quenched after isothermal holding at 850℃, and the hardness further increased. Colony appeared after deformation at 850℃ subsequent water quenching, and the hardness reached the maximum value (Hv584). This was attributed to the grain boundaries strengthening. The microstructure composed of α phase, lamellar colonies α/β and colony when the specimen was isothermal held at 600℃ after deformation at 850℃. Cooling and isothermal holding after deformation resulted in an increase of the width of α phase and colony. It offered a range of 324-706 nm for equiaxed grains. This resulted in the hardness decrease.
It is important to understand the microstructural evolution during water quenching after different processing conditions in order to obtain optimum mechanical properties of Ti-6Al-4V alloy. The thermal simulation of Ti-6Al-4V alloy was conducted using a thermomechanical simulator. The results have shown that a fully martensitic microstructure was obtained after solution treatment. Water-quenching after solution resulted in hardness increase, and this was attributed to the presence of α′ and α″. The lamellar structure formed when the specimen was water-quenched after isothermal holding at 850℃, and the hardness further increased. Colony appeared after deformation at 850℃ subsequent water quenching, and the hardness reached the maximum value (Hv584). This was attributed to the grain boundaries strengthening. The microstructure composed of α phase, lamellar colonies α/β and colony when the specimen was isothermal held at 600℃ after deformation at 850℃. Cooling and isothermal holding after deformation resulted in an increase of the width of α phase and colony. It offered a range of 324-706 nm for equiaxed grains. This resulted in the hardness decrease.
2020, 49(9):3012-3020.
DOI: 10.12442/j.issn.1002-185X.E20190095
Abstract:
As a new severe plastic deformation (SPD) method, equal-channel double angular pressing (ECDAP) is developed based on equal-channel angular pressing (ECAP) to reduce the offset load. The deformation behaviors of commercial sintered pure tungsten (W) during single pass ECDAP were analyzed quantitatively in this paper by means of finite element simulation and experiment investigation. The results show that, compared with ECAP, the local force of the die distributes more homogeneously and the offset load of the punch is improved with the same parameters. Meanwhile, the average effective strain introduced by ECDAP is similar to that of ECAP. Nevertheless, the uniformity of strain distribution is also greatly improved owing to the secondary shear deformation. In addition, grain size decreases to 1.77 μm in the secondary shear deformation zone and the grains are elongated obviously in the angle zone. Hence, the microhardness was enhanced because of the Hall-Petch strengthening and strain strengthening. These results indicate that the ECDAP process is a promising approach for producing ultra-fine grains metallic materials.
As a new severe plastic deformation (SPD) method, equal-channel double angular pressing (ECDAP) is developed based on equal-channel angular pressing (ECAP) to reduce the offset load. The deformation behaviors of commercial sintered pure tungsten (W) during single pass ECDAP were analyzed quantitatively in this paper by means of finite element simulation and experiment investigation. The results show that, compared with ECAP, the local force of the die distributes more homogeneously and the offset load of the punch is improved with the same parameters. Meanwhile, the average effective strain introduced by ECDAP is similar to that of ECAP. Nevertheless, the uniformity of strain distribution is also greatly improved owing to the secondary shear deformation. In addition, grain size decreases to 1.77 μm in the secondary shear deformation zone and the grains are elongated obviously in the angle zone. Hence, the microhardness was enhanced because of the Hall-Petch strengthening and strain strengthening. These results indicate that the ECDAP process is a promising approach for producing ultra-fine grains metallic materials.
wangcuiping
,
luyong
,
dengyuling
,
guoyihui
,
huangyixiong
,
chenmenghua
,
lizhou
,
liuxingjun
,
liuguozheng
2020, 49(9):3021-3029.
DOI: 10.12442/j.issn.1002-185X.20190463
Abstract:
The CALPHAD method was used to optimize and calculate the phase diagrams of Nd-Dy, Dy-B binary systems and Fe-B-Dy, Dy-Fe-Nd and B-Dy-Nd ternary systems. The thermodynamic databases of Nd-Fe-B-Dy quaternary alloys were established by the thermodynamic parameters of binary and ternary sub-systems reported in the literature and took into account the consistency of the thermodynamic models. The longitudinal cross-section phase diagrams of Nd-Fe-B-Dy quaternary alloy Nd16-xDyxFe77B7 (x≤5 at.%) were predicted by using these databases. At the same time, the variation of the fractions of each phase of the permanent magnet alloy with different Dy content under equilibrium solidification was analyzed. These results could be helpful for the microstructure design of the Dy-doped NdFeB permanent magnet alloy and the selection of the preparation process parameters.
The CALPHAD method was used to optimize and calculate the phase diagrams of Nd-Dy, Dy-B binary systems and Fe-B-Dy, Dy-Fe-Nd and B-Dy-Nd ternary systems. The thermodynamic databases of Nd-Fe-B-Dy quaternary alloys were established by the thermodynamic parameters of binary and ternary sub-systems reported in the literature and took into account the consistency of the thermodynamic models. The longitudinal cross-section phase diagrams of Nd-Fe-B-Dy quaternary alloy Nd16-xDyxFe77B7 (x≤5 at.%) were predicted by using these databases. At the same time, the variation of the fractions of each phase of the permanent magnet alloy with different Dy content under equilibrium solidification was analyzed. These results could be helpful for the microstructure design of the Dy-doped NdFeB permanent magnet alloy and the selection of the preparation process parameters.
2020, 49(9):3030-3034.
DOI: 10.12442/j.issn.1002-185X.20200082
Abstract:
This study develops an effective, simple, and low-cost method through metal–organic chemical vapor deposition for manufacturing carbonyl iron (CI)-coated hollow cenospheres(Ce) as new composites for microwave absorption. Structure and morphology analyses demonstrate that the composites have a complete core/shell structure with Ce as the core and CI layers as the shell. Compared with Ce, the composites have higher complex permeability and permittivity, indicating their improved absorption capacity. The measured electromagnetic parameters are used to analog and calculate the reflectance curves of Ce and Ce@CI coating under the condition of thickness d=2mm. The absorption peak of the Ce@CI sample shifts to the high frequency, and the minimum reflection peak decreases to ? 26.2dB. The frequencyat less than – 10dB bandwidth increases to 6 GHz, which covered the entire Ku band.
This study develops an effective, simple, and low-cost method through metal–organic chemical vapor deposition for manufacturing carbonyl iron (CI)-coated hollow cenospheres(Ce) as new composites for microwave absorption. Structure and morphology analyses demonstrate that the composites have a complete core/shell structure with Ce as the core and CI layers as the shell. Compared with Ce, the composites have higher complex permeability and permittivity, indicating their improved absorption capacity. The measured electromagnetic parameters are used to analog and calculate the reflectance curves of Ce and Ce@CI coating under the condition of thickness d=2mm. The absorption peak of the Ce@CI sample shifts to the high frequency, and the minimum reflection peak decreases to ? 26.2dB. The frequencyat less than – 10dB bandwidth increases to 6 GHz, which covered the entire Ku band.
2020, 49(9):3035-3044.
DOI: 10.12442/j.issn.1002-185X.20200178
Abstract:
Compared with the traditional non-ferrous materials, non-ferrous metal matrix composites have better oxidation resistance, high heat resistance, high specific strength, high specific modulus, wear resistance and high service life. Among the various reinforcements of non-ferrous metal matrix composites, the compatibility of the interface between non-metallic fiber (C/C, SiC) and metal matrix is the key to restrict the performance of metal matrix composites, and the good compatibility between metal fiber and metal matrix can effectively improve the performance of metal matrix composites. The preparation technology of metal fiber reinforced non-ferrous metal matrix composites mainly includes diffusion bonding method, liquid infiltration method, pressure casting method, coating hot pressing method and double roll rolling method. In this paper, the preparation methods, microstructure, interface characteristics and mechanical properties of steel fiber reinforced non-ferrous metal matrix composites (Al, Mg, Cu, Zn and Zr) were summarized. Some future researches and developments of steel fiber reinforced non-ferrous metal matrix composites were highlighted.
Compared with the traditional non-ferrous materials, non-ferrous metal matrix composites have better oxidation resistance, high heat resistance, high specific strength, high specific modulus, wear resistance and high service life. Among the various reinforcements of non-ferrous metal matrix composites, the compatibility of the interface between non-metallic fiber (C/C, SiC) and metal matrix is the key to restrict the performance of metal matrix composites, and the good compatibility between metal fiber and metal matrix can effectively improve the performance of metal matrix composites. The preparation technology of metal fiber reinforced non-ferrous metal matrix composites mainly includes diffusion bonding method, liquid infiltration method, pressure casting method, coating hot pressing method and double roll rolling method. In this paper, the preparation methods, microstructure, interface characteristics and mechanical properties of steel fiber reinforced non-ferrous metal matrix composites (Al, Mg, Cu, Zn and Zr) were summarized. Some future researches and developments of steel fiber reinforced non-ferrous metal matrix composites were highlighted.
19 High Temperature Deformation Behavior and Dynamic Recrystallization Mechanism of TB18 Titanium Alloy
Li Shaoqian
,
Hu Shengshuang
,
Gong Zhanpeng
,
Cui Linlin
,
Lei Jinwen
,
Wang Kaixuan
,
Ju Biao
,
Fan Yanjie
,
Fu Jie
2020, 49(9):3045-3051.
DOI: 10.12442/j.issn.1002-185X.20200162
Abstract:
In this paper, the high temperature deformation behavior and the dynamic recrystallization mechanism of TB18 titanium alloy in 700℃ ~ 900℃ with the strain rate of 0.01 ~ 10 s-1 were studied using the Gleeble 3800 simulator and the electron backscatter diffraction (EBSD) technique. The value of flow stress of the alloy was sensitive to the strain rate and the deformation temperature. In the initial stage of the deformation, the flow stress would soften rapidly after reaching the peak stress, and then it increased to different levels. The Arrhenius-type constitutive equations of the high temperature deformation of TB18 titanium alloy in both α +β dual-phase region and β single-phase region were obtained through data regression. The apparent activation energy in both α +β dual-phase region and β single-phase region were calculated to be 340 kJ/mol and 185 kJ/mol, respectively. The deformation softening mechanism was mainly controlled by dynamic recrystallization of β phase in α+β dual-phase region and dynamic recovery of β phase in β single-phase region. According to the EBSD maps, the metallographic observation and the characteristics of stress-strain curves, it was concluded that the geometric dynamic recrystallization (GDRX) prevailed when the deformation was conducted at high temperature and low strain rate (900°C, 0.01 s-1). As the lower temperature or the higher strain rate was applied, the discontinuous dynamic recrystallization (DDRX) took place at the initial stage of the deformation and the continuous dynamic recrystallization (CDRX) was shown after the strain increased.
In this paper, the high temperature deformation behavior and the dynamic recrystallization mechanism of TB18 titanium alloy in 700℃ ~ 900℃ with the strain rate of 0.01 ~ 10 s-1 were studied using the Gleeble 3800 simulator and the electron backscatter diffraction (EBSD) technique. The value of flow stress of the alloy was sensitive to the strain rate and the deformation temperature. In the initial stage of the deformation, the flow stress would soften rapidly after reaching the peak stress, and then it increased to different levels. The Arrhenius-type constitutive equations of the high temperature deformation of TB18 titanium alloy in both α +β dual-phase region and β single-phase region were obtained through data regression. The apparent activation energy in both α +β dual-phase region and β single-phase region were calculated to be 340 kJ/mol and 185 kJ/mol, respectively. The deformation softening mechanism was mainly controlled by dynamic recrystallization of β phase in α+β dual-phase region and dynamic recovery of β phase in β single-phase region. According to the EBSD maps, the metallographic observation and the characteristics of stress-strain curves, it was concluded that the geometric dynamic recrystallization (GDRX) prevailed when the deformation was conducted at high temperature and low strain rate (900°C, 0.01 s-1). As the lower temperature or the higher strain rate was applied, the discontinuous dynamic recrystallization (DDRX) took place at the initial stage of the deformation and the continuous dynamic recrystallization (CDRX) was shown after the strain increased.
2020, 49(9):3052-3058.
DOI: 10.12442/j.issn.1002-185X.20190670
Abstract:
The influence of different ratios of La and Ag under the condition of T6 peak aging treatment and different thermal exposure were investigated. The microstructures and tensile properties of Weldalite049 aluminum alloy were analyzed by SEM, TEM and tensile properties testing. The aim is to investigate the method of substituting a small amount of rare earth La for higher price Ag in precondition of satisfying mechanical requirements. It is proved that the tensile strength of Weldalite 049 alloy with 0.05wt.% La instead of 0.2wt.% Ag is 615.5MPa after T6 treatment, which is higher than that of Weldalite 049 alloy 611.1MPa. The mechanical properties of Weldalite 049 alloy with 0.1wt.% La but without Ag remain at a high level under thermal exposure at 175 C/60h.
The influence of different ratios of La and Ag under the condition of T6 peak aging treatment and different thermal exposure were investigated. The microstructures and tensile properties of Weldalite049 aluminum alloy were analyzed by SEM, TEM and tensile properties testing. The aim is to investigate the method of substituting a small amount of rare earth La for higher price Ag in precondition of satisfying mechanical requirements. It is proved that the tensile strength of Weldalite 049 alloy with 0.05wt.% La instead of 0.2wt.% Ag is 615.5MPa after T6 treatment, which is higher than that of Weldalite 049 alloy 611.1MPa. The mechanical properties of Weldalite 049 alloy with 0.1wt.% La but without Ag remain at a high level under thermal exposure at 175 C/60h.
2020, 49(9):3059-3064.
DOI: 10.12442/j.issn.1002-185X.20190687
Abstract:
Yttria-stabilized zirconia(YSZ)/Al2O3 composite materials were prepared by mechanically mixing, dry pressing and high temperature sintering of YSZ with Al2O3 and Al(NO3)3 as aluminum sources, respectively. The effects of aluminum sources and addition amounts on the sinterability, electrical conductivity and mechanical property of YSZ/Al2O3 composites were investigated by means of scanning electron microscopy, electrochemical impedance spectroscopy and three-point bending test. The results show that addition of suitable amounts of Al2O3 or Al(NO3)3 into YSZ can promote the sinterability of YSZ and improve its electrical conductivity and flexural strength. Sinterability and electrical conductivity of YSZ/Al2O3 composites using Al2O3 as aluminum source are higher than those of using Al(NO3)3, but mechanical strengths exhibit the contrary trend at the same addition amount. When 0.5 wt.% of Al2O3 is added into YSZ, the relative density of 98.8% and the electrical conductivity of 0.0703 S·cm-1 at 800 ℃ are achieved on YSZ/Al2O3 composite electrolyte sintered at 1350 ℃ for 10 h. The electrolyte-supported unit cell constructed by the YSZ/Al2O3 composite electrolyte gives the maximum power density of 308 mW·cm-2 at 800 ℃ using H2 as the fuel, which is higher than that of the pure YSZ electrolyte and exhibits good stability.
Yttria-stabilized zirconia(YSZ)/Al2O3 composite materials were prepared by mechanically mixing, dry pressing and high temperature sintering of YSZ with Al2O3 and Al(NO3)3 as aluminum sources, respectively. The effects of aluminum sources and addition amounts on the sinterability, electrical conductivity and mechanical property of YSZ/Al2O3 composites were investigated by means of scanning electron microscopy, electrochemical impedance spectroscopy and three-point bending test. The results show that addition of suitable amounts of Al2O3 or Al(NO3)3 into YSZ can promote the sinterability of YSZ and improve its electrical conductivity and flexural strength. Sinterability and electrical conductivity of YSZ/Al2O3 composites using Al2O3 as aluminum source are higher than those of using Al(NO3)3, but mechanical strengths exhibit the contrary trend at the same addition amount. When 0.5 wt.% of Al2O3 is added into YSZ, the relative density of 98.8% and the electrical conductivity of 0.0703 S·cm-1 at 800 ℃ are achieved on YSZ/Al2O3 composite electrolyte sintered at 1350 ℃ for 10 h. The electrolyte-supported unit cell constructed by the YSZ/Al2O3 composite electrolyte gives the maximum power density of 308 mW·cm-2 at 800 ℃ using H2 as the fuel, which is higher than that of the pure YSZ electrolyte and exhibits good stability.
2020, 49(9):3065-3070.
DOI: 10.12442/j.issn.1002-185X.20200022
Abstract:
The effect of alloying concentration x (x=0~2.2%,atom fraction) to several parameters such as Cauchy pressure, Elastic modulus E, the shear modulus G and their ratio G/B0 of B2-NiAl supercells alloyed by Cr and Ce, alone or together, are calculated in the framework of Virtual Crystal Approximation by the first-principles pseudopotential plane-wave method. The shear modulus G and elastic modulus E of B2-NiAl alloy were significantly increased when Cr occupied the Ni atom site in B2-NiAl crystals, while the G and E will be reduced when Ce occupied the Al atom site. With the alloying concentration increased to 2.1%, the ductility of B2-NiAl crystals can be improved with Cr occupied the Al atom site. It is worth emphasizing that the ductility of B2-NiAl crystals was improved more significantly when Ce and Cr replaced Al atom site simultaneously than that alloyed by Ce or Cr alone, especially the alloying concentration x is 2.0%. The electronic density of states shows that Cr atoms or Cr cooperation with Ce atoms all can weaken the hybridization effect of the main bonding peaks of Ni(d)-Ni(d) and decrease the directivity of the main bonding peaks in B2-NiAl crystal. The calculation result herein explains the phenomenon that the room temperature ductility of B2-NiAl alloy is enhanced obviously alloyed by Cr or Cr cooperation with Ce.
The effect of alloying concentration x (x=0~2.2%,atom fraction) to several parameters such as Cauchy pressure, Elastic modulus E, the shear modulus G and their ratio G/B0 of B2-NiAl supercells alloyed by Cr and Ce, alone or together, are calculated in the framework of Virtual Crystal Approximation by the first-principles pseudopotential plane-wave method. The shear modulus G and elastic modulus E of B2-NiAl alloy were significantly increased when Cr occupied the Ni atom site in B2-NiAl crystals, while the G and E will be reduced when Ce occupied the Al atom site. With the alloying concentration increased to 2.1%, the ductility of B2-NiAl crystals can be improved with Cr occupied the Al atom site. It is worth emphasizing that the ductility of B2-NiAl crystals was improved more significantly when Ce and Cr replaced Al atom site simultaneously than that alloyed by Ce or Cr alone, especially the alloying concentration x is 2.0%. The electronic density of states shows that Cr atoms or Cr cooperation with Ce atoms all can weaken the hybridization effect of the main bonding peaks of Ni(d)-Ni(d) and decrease the directivity of the main bonding peaks in B2-NiAl crystal. The calculation result herein explains the phenomenon that the room temperature ductility of B2-NiAl alloy is enhanced obviously alloyed by Cr or Cr cooperation with Ce.
Bai Guanghai
,
Xue Fei
,
Liu Erwei
,
Zhang Yanwei
,
Geng Jianqiao
,
Shang Can
,
Dang Jianwei
,
Liu Xiangbin
,
Yu Weiwei
2020, 49(9):3071-3076.
DOI: 10.12442/j.issn.1002-185X.20200116
Abstract:
FeCrAl / ZrNbCu dual layer tube is one of the candidate materials for accident tolerant fuel cladding, which takes the advantages of ZrNbCu alloy and FeCrAl alloy into account. In this paper, the high-temperature steam oxidation behavior of FeCrAl /ZrNbCu dual layer tube is studied. The results show that the outer layer FeCrAl material has excellent high temperature steam oxidation resistance, and the inner ZrNbCu alloy layer can be effectively protected by FeCrAl alloy. The concave and convex morphology of oxide film of FeCrAl alloy is formed, and the oxidation products are Fe2O3, FeCr2O4, Cr2O3 and Al2O3. The oxide film of ZrNbCu alloy grows perpendicular to the surface, and the oxidation products are ZrO2 and Nb2O5. Element diffusion at the interface of the dual layer tube can not be found when it is oxidized at 1000 ℃; there is obvious element diffusion at the interface when it is oxidized at 1100 ℃ and 1200 ℃. From the outer side to the inner side of the dual layer tube, FeCrAl oxide film, FeCrAl alloy, FeCrAl-ZrNbCu diffusion layer, ZrNbCu alloy and ZrNbCu oxide film are formed; the original mechanical bonding transforms to metallurgical bonding when the temperature is above 1100 ℃.
FeCrAl / ZrNbCu dual layer tube is one of the candidate materials for accident tolerant fuel cladding, which takes the advantages of ZrNbCu alloy and FeCrAl alloy into account. In this paper, the high-temperature steam oxidation behavior of FeCrAl /ZrNbCu dual layer tube is studied. The results show that the outer layer FeCrAl material has excellent high temperature steam oxidation resistance, and the inner ZrNbCu alloy layer can be effectively protected by FeCrAl alloy. The concave and convex morphology of oxide film of FeCrAl alloy is formed, and the oxidation products are Fe2O3, FeCr2O4, Cr2O3 and Al2O3. The oxide film of ZrNbCu alloy grows perpendicular to the surface, and the oxidation products are ZrO2 and Nb2O5. Element diffusion at the interface of the dual layer tube can not be found when it is oxidized at 1000 ℃; there is obvious element diffusion at the interface when it is oxidized at 1100 ℃ and 1200 ℃. From the outer side to the inner side of the dual layer tube, FeCrAl oxide film, FeCrAl alloy, FeCrAl-ZrNbCu diffusion layer, ZrNbCu alloy and ZrNbCu oxide film are formed; the original mechanical bonding transforms to metallurgical bonding when the temperature is above 1100 ℃.
2020, 49(9):3077-3083.
DOI: 10.12442/j.issn.1002-185X.20190719
Abstract:
For the radial high-temperature superconducting magnetic bearing used in centrifugal helium cold compressor, the magnetic field calculation and structural design method of permanent magnet rotor are given, and the calculation of radial force and radial stiffness is carried out. A superconducting bearing performance measurement platform was built, and bearing rotor space magnetic field and bearing performance were measured. The calculation and measurement results show that the magnetic field calculation method is feasible and the result is accurate. The maximum external magnetic field at 1 mm from the outer surface of the permanent magnet rotor is about 0.5 T. The calculated radial force under field cooling and zero field cooling conditions both increase with the increase of the rotor eccentricity, which is in good agreement with the measurement results in linearity and trend. The measured radial stiffness value of the measured bearing in this paper is 362.4 N/mm, which is close to the calculated radial stiffness 334.594 N/mm, under field cooling conditions. The radial force calculation method described in this paper can be used for the qualitative radial stiffness calculation and design of high-temperature superconducting magnetic bearings, which has certain guiding significance for the application research of superconducting bearings.
For the radial high-temperature superconducting magnetic bearing used in centrifugal helium cold compressor, the magnetic field calculation and structural design method of permanent magnet rotor are given, and the calculation of radial force and radial stiffness is carried out. A superconducting bearing performance measurement platform was built, and bearing rotor space magnetic field and bearing performance were measured. The calculation and measurement results show that the magnetic field calculation method is feasible and the result is accurate. The maximum external magnetic field at 1 mm from the outer surface of the permanent magnet rotor is about 0.5 T. The calculated radial force under field cooling and zero field cooling conditions both increase with the increase of the rotor eccentricity, which is in good agreement with the measurement results in linearity and trend. The measured radial stiffness value of the measured bearing in this paper is 362.4 N/mm, which is close to the calculated radial stiffness 334.594 N/mm, under field cooling conditions. The radial force calculation method described in this paper can be used for the qualitative radial stiffness calculation and design of high-temperature superconducting magnetic bearings, which has certain guiding significance for the application research of superconducting bearings.
2020, 49(9):3084-3090.
DOI: 10.12442/j.issn.1002-185X.20190737
Abstract:
The vacuum slab models of crystal faces (0-11),(-101),(110) and (-1-10) in WO3 crystal were calculated by the molecular simulation software Material Studio7.0,and the total energy, surface energy and electronic structure were calculated by CASTEP program.Using the Morphology program,the growth habits of WO3 crystal and the slab model of each crystal face were predicted by BFDH rule.The results of calculation show that the energy stability of WO3 crystal is poor in the process of crystal growth when face (110) is the mainly unfold face ,while the energy state of the WO3 crystal would be stable when face (0-11) is mainly unfolded.The front valence electron of face (110) with the smallest Fermi energy is not active, and there is relative stability of electronic structure dynamic.The front valence electron of face (-1-10) with the highest Fermi energy is active, which means there is activity point on this face that can be bonded to crystal growth martix.The slab model of face (0-11) has the smallest minimum energy region width and the largest state density peak value,which indicates the inner electron is relatively stable.The predicate results of the BFDH rule show that the growth habit of the WO3 crystal is consist with the slab model，and tends to grow to cubic crystal.In addition,the most important growth faces in WO3 crystal are (001) and (00-1).
The vacuum slab models of crystal faces (0-11),(-101),(110) and (-1-10) in WO3 crystal were calculated by the molecular simulation software Material Studio7.0,and the total energy, surface energy and electronic structure were calculated by CASTEP program.Using the Morphology program,the growth habits of WO3 crystal and the slab model of each crystal face were predicted by BFDH rule.The results of calculation show that the energy stability of WO3 crystal is poor in the process of crystal growth when face (110) is the mainly unfold face ,while the energy state of the WO3 crystal would be stable when face (0-11) is mainly unfolded.The front valence electron of face (110) with the smallest Fermi energy is not active, and there is relative stability of electronic structure dynamic.The front valence electron of face (-1-10) with the highest Fermi energy is active, which means there is activity point on this face that can be bonded to crystal growth martix.The slab model of face (0-11) has the smallest minimum energy region width and the largest state density peak value,which indicates the inner electron is relatively stable.The predicate results of the BFDH rule show that the growth habit of the WO3 crystal is consist with the slab model，and tends to grow to cubic crystal.In addition,the most important growth faces in WO3 crystal are (001) and (00-1).
2020, 49(9):3091-3098.
DOI: 10.12442/j.issn.1002-185X.20190723
Abstract:
A three-dimensional cellular automata (3D-CA) model was established to visualize and quantitatively predict the microstructural evolution of AZ31 magnesium alloy during hot deformation by thermal compression test and electronic backscatter characterization (EBSD). According to the true stress-strain curve obtained from the test, the values of the parameters of the 3D-CA model under the test conditions are determined, and the relationship between the parameters of the model and the deformation conditions (strain, deformation temperature and strain rate) is established. The flow behavior and microstructure evolution of AZ31 magnesium alloy during hot deformation were simulated and discussed by using the established 3D-CA model. The results show that the recrystallization integral increases with the increase of strain, and increases with the increase of deformation temperature or the decrease of strain rate. Raising strain rate or decreasing temperature can refine recrystallized grains. The simulation results are in good agreement with the experimental results. The relative error is between 4.5% and 16.2%. The 3D-CA model can accurately predict the microstructure evolution of magnesium alloy AZ31.
A three-dimensional cellular automata (3D-CA) model was established to visualize and quantitatively predict the microstructural evolution of AZ31 magnesium alloy during hot deformation by thermal compression test and electronic backscatter characterization (EBSD). According to the true stress-strain curve obtained from the test, the values of the parameters of the 3D-CA model under the test conditions are determined, and the relationship between the parameters of the model and the deformation conditions (strain, deformation temperature and strain rate) is established. The flow behavior and microstructure evolution of AZ31 magnesium alloy during hot deformation were simulated and discussed by using the established 3D-CA model. The results show that the recrystallization integral increases with the increase of strain, and increases with the increase of deformation temperature or the decrease of strain rate. Raising strain rate or decreasing temperature can refine recrystallized grains. The simulation results are in good agreement with the experimental results. The relative error is between 4.5% and 16.2%. The 3D-CA model can accurately predict the microstructure evolution of magnesium alloy AZ31.
27 Preparation and Electrochemical Performance Improvement of Alkaline Earth Metal Ca Doped LNF Cathode
2020, 49(9):3099-3106.
DOI: 10.12442/j.issn.1002-185X.20190785
Abstract:
In recent years, LaNi0.6Fe0.4O3-δcathode materials have pay a attention to chromium poisoning performance under metal interconnects, but it has relatively low electrochemical performance. This paper improves the electrochemical performance of LNF cathode by Ca doping, La1-xCaxNi0.6Fe0.4O3-δ(x=0、0.05、0.10、0.15、0.20) cathode material was prepared by a glycine combustion method. The phase composition of the material was characterized by X-Ray diffraction. The microstructure of the cathode material was observed by SEM. The chemical forms of elements on the surface of cathode materials was analyzed by XPS.The electrochemical activity of the cathode material was analyzed by an AC impedance spectroscopy. The results show that the activation energy of oxygen reduction reaction decreases with the increase of Ca2+ doping content in La1-xCaxNi0.6Fe0.4O3-δcathode material, which is consistent with the DRT (Distribution of relaxation times) analysis. The La0.8Ca0.2Ni0.6Fe0.4O3-δcathode material has the lowest polarization resistance (0.88 Ωcm2) at 750℃, and exhibits more excellent oxygen catalytic activity than the undoped LNF material, making the LCNF cathode have a broader application prospect in IT-SOFC.
In recent years, LaNi0.6Fe0.4O3-δcathode materials have pay a attention to chromium poisoning performance under metal interconnects, but it has relatively low electrochemical performance. This paper improves the electrochemical performance of LNF cathode by Ca doping, La1-xCaxNi0.6Fe0.4O3-δ(x=0、0.05、0.10、0.15、0.20) cathode material was prepared by a glycine combustion method. The phase composition of the material was characterized by X-Ray diffraction. The microstructure of the cathode material was observed by SEM. The chemical forms of elements on the surface of cathode materials was analyzed by XPS.The electrochemical activity of the cathode material was analyzed by an AC impedance spectroscopy. The results show that the activation energy of oxygen reduction reaction decreases with the increase of Ca2+ doping content in La1-xCaxNi0.6Fe0.4O3-δcathode material, which is consistent with the DRT (Distribution of relaxation times) analysis. The La0.8Ca0.2Ni0.6Fe0.4O3-δcathode material has the lowest polarization resistance (0.88 Ωcm2) at 750℃, and exhibits more excellent oxygen catalytic activity than the undoped LNF material, making the LCNF cathode have a broader application prospect in IT-SOFC.
2020, 49(9):3107-3114.
DOI: 10.12442/j.issn.1002-185X.20190791
Abstract:
The hot deformation behavior and dynamic recrystallization (DRX) of Ti-62A alloy at 800, 850, 900 and 950 ℃and strain rates of 0.001, 0.01, 0.1 and 1 s-1 were studied by hot compression experiments on Gleeble-3800 thermal simulator. The results show that the flow stress of Ti-62A alloy is significantly affected by strain rate and deformation temperature. The flow stress decreases with the increase of temperature and the decrease of strain rate. At 900~950 ℃ and strain rate of 0.01~1 s-1, the thermal deformation stress-strain curve of Ti-62A alloy belongs to dynamic recovery type, and the thermal deformation mechanism of the alloy is mainly controlled by dislocation movement, and its dynamic softening mechanism includes grain boundary sliding, dislocation cancellation and climbing mechanism; During hot deformation of Ti-62A alloy, dynamic recrystallization are more likely to occur at higher temperatures and lower strain rates, i.e. 950 ℃and 0.001 s-1. Based on the classical dislocation density theory and DRX dynamics theory, a two-stage constitutive model of work hardening — dynamic recovery and DRX softening effect is established. The simulation results of DEFORM-3D software confirm that the constitutive model based on DRX softening effect has high accuracy in predicting the thermal deformation behavior of Ti-62A alloy in the dynamic recrystallization stage, which can provide technical reference for the actual production process.
The hot deformation behavior and dynamic recrystallization (DRX) of Ti-62A alloy at 800, 850, 900 and 950 ℃and strain rates of 0.001, 0.01, 0.1 and 1 s-1 were studied by hot compression experiments on Gleeble-3800 thermal simulator. The results show that the flow stress of Ti-62A alloy is significantly affected by strain rate and deformation temperature. The flow stress decreases with the increase of temperature and the decrease of strain rate. At 900~950 ℃ and strain rate of 0.01~1 s-1, the thermal deformation stress-strain curve of Ti-62A alloy belongs to dynamic recovery type, and the thermal deformation mechanism of the alloy is mainly controlled by dislocation movement, and its dynamic softening mechanism includes grain boundary sliding, dislocation cancellation and climbing mechanism; During hot deformation of Ti-62A alloy, dynamic recrystallization are more likely to occur at higher temperatures and lower strain rates, i.e. 950 ℃and 0.001 s-1. Based on the classical dislocation density theory and DRX dynamics theory, a two-stage constitutive model of work hardening — dynamic recovery and DRX softening effect is established. The simulation results of DEFORM-3D software confirm that the constitutive model based on DRX softening effect has high accuracy in predicting the thermal deformation behavior of Ti-62A alloy in the dynamic recrystallization stage, which can provide technical reference for the actual production process.
2020, 49(9):3115-3121.
DOI: 10.12442/j.issn.1002-185X.20190746
Abstract:
Powder Metallurgy is an important part of the forming process for metal materials. However, most material models are not able to simulate the variation of mechanical characters during the compressing process. In this paper, the Drucker-Prager/Cap model is modified by including the fully densified metal yield strength. This modified Drucker-Prager/Cap model can limit the yield strength of metal powder within the Von Mises surface of a fully densified metal. With the compressing process, the powder’s surface is infinitely close to Von Mises surface. By comparing of the model prediction and the published experimental results, this modified model works well in terms of accuracy. And, it is applied to the simulation of a hot isostatic pressing for a supper alloy. The prediction of the deformation as well as the stress distribution by this model is more accurate compared to the real test than that by the traditional Drucker-Prager/Cap model.
Powder Metallurgy is an important part of the forming process for metal materials. However, most material models are not able to simulate the variation of mechanical characters during the compressing process. In this paper, the Drucker-Prager/Cap model is modified by including the fully densified metal yield strength. This modified Drucker-Prager/Cap model can limit the yield strength of metal powder within the Von Mises surface of a fully densified metal. With the compressing process, the powder’s surface is infinitely close to Von Mises surface. By comparing of the model prediction and the published experimental results, this modified model works well in terms of accuracy. And, it is applied to the simulation of a hot isostatic pressing for a supper alloy. The prediction of the deformation as well as the stress distribution by this model is more accurate compared to the real test than that by the traditional Drucker-Prager/Cap model.
2020, 49(9):3122-3128.
DOI: 10.12442/j.issn.1002-185X.20190645
Abstract:
The microstructure and properties of DZ125 as-deposited and two-stage aging heat treated samples were analyzed by laser deposition single-layer multi-layer experiments on the casting substrate along the longitudinal direction of DZ125. The results show that the microstructure of the sedimentary repair area is planar crystal, columnar crystal and equiaxed crystal structure from the bottom to the top. The repaired area is mainly MC carbide. The heat affected zone will be decomposed into M23C6 by MC due to the input of heat. Compared with the microstructure, after the two-stage aging heat treatment, a new grain boundary is formed in the repaired area, and some MC carbides are decomposed into M6C and M23C6, and the γ" phase size is slightly increased, about 600-800 nm, and the distribution is uniform; The size of the carbides in the area is slightly reduced, the size of the γ" phase is still increasing, and it is cubic. The tensile strength of the two-stage aging heat treatment specimen at 1000 °C is 516 MPa, and the yield strength is 386 MPa, which is 89.7% of the casting respectively. And 97.7%, the elongation rate is 13.6%, reaching 43.9% of the casting; the average hardness of the repaired sample after heat treatment is 473 HV0.3, which is higher than the average hardness of the as-deposited sample 433 HV0.3, and the heat-treated state and the deposited sample along the repair zone, heat The hardness of the affected zone to the matrix is decreasing.
The microstructure and properties of DZ125 as-deposited and two-stage aging heat treated samples were analyzed by laser deposition single-layer multi-layer experiments on the casting substrate along the longitudinal direction of DZ125. The results show that the microstructure of the sedimentary repair area is planar crystal, columnar crystal and equiaxed crystal structure from the bottom to the top. The repaired area is mainly MC carbide. The heat affected zone will be decomposed into M23C6 by MC due to the input of heat. Compared with the microstructure, after the two-stage aging heat treatment, a new grain boundary is formed in the repaired area, and some MC carbides are decomposed into M6C and M23C6, and the γ" phase size is slightly increased, about 600-800 nm, and the distribution is uniform; The size of the carbides in the area is slightly reduced, the size of the γ" phase is still increasing, and it is cubic. The tensile strength of the two-stage aging heat treatment specimen at 1000 °C is 516 MPa, and the yield strength is 386 MPa, which is 89.7% of the casting respectively. And 97.7%, the elongation rate is 13.6%, reaching 43.9% of the casting; the average hardness of the repaired sample after heat treatment is 473 HV0.3, which is higher than the average hardness of the as-deposited sample 433 HV0.3, and the heat-treated state and the deposited sample along the repair zone, heat The hardness of the affected zone to the matrix is decreasing.
31 Synthesis and Electrochemical Performance of Al2O3 Coated LiNi0.03Co0.05Mn1.92O4 as Cathode Material
Wang Shimin
,
Liu Honglei
,
Guo Junming
,
Xiang Mingwu
,
Su Changwei
,
Bai Hongli
,
Liu Xiaofang
,
Bai Wei
2020, 49(9):3129-3135.
DOI: 10.12442/j.issn.1002-185X.20190666
Abstract:
Al2O3-coated LiNi0.03Co0.05Mn1.92O4 cathode materials were prepared by combustion method with aluminum nitrate nonahydrate as raw material. The structure and morphology of the materials were analyzed by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM), and the electrochemical performance were characterized by galvanostatic charge-discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It was found that Al2O3 coating did not change the spinel structure of LiNi0.03Co0.05Mn1.92O4, and the coating thickness was about 10.6 nm. The LiNi0.03Co0.05Mn1.92O4@Al2O3 material exhibited excellent electrochemical performance. The initial discharge capacity of the Al2O3 coated materials were 119.9mAh g-1 at 1C rate and 106.3 mAh?g-1 at 10 C rate, the capacity retention were 88.4 % and 78.2% after charge/discharge cycles for 500 times. While the initial discharge capacity of uncoated LiNi0.03Co0.05Mn1.92O4 were 121.2 mAh?g-1 and 104 mAh?g-1 at different rates, the retention rate were 84.1% and 67.6% after 500 cycles, respectively. Besides that, the LiNi0.03Co0.05Mn1.92O4@Al2O3 had a lower activation energy of 32.92 kJ?mol-1, while 36.24 kJ?mol-1 for the uncoated. The energy barrier needed for lithium ion diffusion was effectively reduced and the electrochemical performance of the cathode material was improved by coating.
Al2O3-coated LiNi0.03Co0.05Mn1.92O4 cathode materials were prepared by combustion method with aluminum nitrate nonahydrate as raw material. The structure and morphology of the materials were analyzed by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM), and the electrochemical performance were characterized by galvanostatic charge-discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It was found that Al2O3 coating did not change the spinel structure of LiNi0.03Co0.05Mn1.92O4, and the coating thickness was about 10.6 nm. The LiNi0.03Co0.05Mn1.92O4@Al2O3 material exhibited excellent electrochemical performance. The initial discharge capacity of the Al2O3 coated materials were 119.9mAh g-1 at 1C rate and 106.3 mAh?g-1 at 10 C rate, the capacity retention were 88.4 % and 78.2% after charge/discharge cycles for 500 times. While the initial discharge capacity of uncoated LiNi0.03Co0.05Mn1.92O4 were 121.2 mAh?g-1 and 104 mAh?g-1 at different rates, the retention rate were 84.1% and 67.6% after 500 cycles, respectively. Besides that, the LiNi0.03Co0.05Mn1.92O4@Al2O3 had a lower activation energy of 32.92 kJ?mol-1, while 36.24 kJ?mol-1 for the uncoated. The energy barrier needed for lithium ion diffusion was effectively reduced and the electrochemical performance of the cathode material was improved by coating.
2020, 49(9):3136-3142.
DOI: 10.12442/j.issn.1002-185X.20190668
Abstract:
Ultra-fine grained (UFG) pure titanium was prepared by equal channel angular pressing (ECAP) and rotary swaging (RS). Low cycle fatigue tests with strain ratios of - 1, - 0.5 and 0.5 for titanium were carried out at room temperature. Microstructure was observed by TEM after the fatigue test. The effects of strain ratio on cyclic hardening and softening properties, cyclic stress-strain relationship and fatigue life of materials were studied. The results show that the cyclic hardening of UFG pure titanium is more obvious with the increase of strain ratio; Low cycle fatigue life of ultra-fine grained pure titanium decreases with increasing strain ratio; Microstructure observation shows that under high strain ratio, the subgrain size is small and the number of subgrains is large, which hinders the movement of dislocations and leads to cyclic hardening.
Ultra-fine grained (UFG) pure titanium was prepared by equal channel angular pressing (ECAP) and rotary swaging (RS). Low cycle fatigue tests with strain ratios of - 1, - 0.5 and 0.5 for titanium were carried out at room temperature. Microstructure was observed by TEM after the fatigue test. The effects of strain ratio on cyclic hardening and softening properties, cyclic stress-strain relationship and fatigue life of materials were studied. The results show that the cyclic hardening of UFG pure titanium is more obvious with the increase of strain ratio; Low cycle fatigue life of ultra-fine grained pure titanium decreases with increasing strain ratio; Microstructure observation shows that under high strain ratio, the subgrain size is small and the number of subgrains is large, which hinders the movement of dislocations and leads to cyclic hardening.
2020, 49(9):3143-3152.
DOI: 10.12442/j.issn.1002-185X.20190669
Abstract:
Kanthal coatings were fabricated by selective laser melting(SLM) with two kinds of powder, 45-60um and 50-70um in diameter. The coatings surface morphology, microstructure, element distribution, phase structure, and microwave attenuation properties were studied by optical microscope, scanning electron microscopy, X-ray diffraction, and cavity characteristic measurement system. The results indicate that Kanthal coatings have the characteristic of rough surface, porous and flaky structure. The quality factor Q of cavity loaded with coatings fabricated by 45-60um Kanthal sphere powder is lower than that of coatings by 50-70?m Kanthal sphere powder, showing better microwave attenuation properties under the frequency of 2985MHz. Al2O3 thin film and micro void generated in the structure of coatings have the effect of scattering microwave and thus reduce microwave reflection. It is also shown that flattened shape of Kanthal coatings is a good way to suppress eddy currents in high-frequeny electromagnetic field and lead to the formation of easy magnetization planes, which is helpful to enhance the microwave attenuation property. The coating thickness has profound effects on interference loss of microwave. Cavity Q with coating thickness of 0.55mm reached the minimum value of 2280. Kanthal coating is composite material and the main mechanism is attributed to magnetic loss.
Kanthal coatings were fabricated by selective laser melting(SLM) with two kinds of powder, 45-60um and 50-70um in diameter. The coatings surface morphology, microstructure, element distribution, phase structure, and microwave attenuation properties were studied by optical microscope, scanning electron microscopy, X-ray diffraction, and cavity characteristic measurement system. The results indicate that Kanthal coatings have the characteristic of rough surface, porous and flaky structure. The quality factor Q of cavity loaded with coatings fabricated by 45-60um Kanthal sphere powder is lower than that of coatings by 50-70?m Kanthal sphere powder, showing better microwave attenuation properties under the frequency of 2985MHz. Al2O3 thin film and micro void generated in the structure of coatings have the effect of scattering microwave and thus reduce microwave reflection. It is also shown that flattened shape of Kanthal coatings is a good way to suppress eddy currents in high-frequeny electromagnetic field and lead to the formation of easy magnetization planes, which is helpful to enhance the microwave attenuation property. The coating thickness has profound effects on interference loss of microwave. Cavity Q with coating thickness of 0.55mm reached the minimum value of 2280. Kanthal coating is composite material and the main mechanism is attributed to magnetic loss.
2020, 49(9):3153-3162.
DOI: 10.12442/j.issn.1002-185X.20190690
Abstract:
The interface evolution of Ti/Ni multi-layered composites produced by 6 cycles accumulative roll bonding after heat treatment was investigated in this study. And the interfacial structural, chemical composition and phase transition temperature of Ti/Ni multi-layered composites with different heat treatment were studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) and a differential scanning calorimeter (DSC). With the annealing time increased, the compounds formed by Ti/Ni interface diffusion transformed from unstable state to stable state, and the composition curves of Ti and Ni elements in the interface gradually change from a cross-steep ladder to two nearly straight parallel lines. With time increases, the microstructure of Ti-rich Ti/Ni composites treated at 720℃ transforming from a regular layered structure to a mixture structure with alternating TiNi and Ti2Ni layers. When the hold time is less than 10h, the structure of TiNi phase is composed of B19" with complex monoclinal structure and B2 with CsCl structure, while when the time is more than 10h, only B19" phase exists. In the process of cooling/heating, a good martensitic and reversible phase transition of A→M/M→A occurred in each sample. With the increase of time, the phase transition hysteresis (Ap-Mp) from 22.4 ℃ of the 1 h heat treatment sample increases to 31.9 ℃ of the 30 h sample.
The interface evolution of Ti/Ni multi-layered composites produced by 6 cycles accumulative roll bonding after heat treatment was investigated in this study. And the interfacial structural, chemical composition and phase transition temperature of Ti/Ni multi-layered composites with different heat treatment were studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) and a differential scanning calorimeter (DSC). With the annealing time increased, the compounds formed by Ti/Ni interface diffusion transformed from unstable state to stable state, and the composition curves of Ti and Ni elements in the interface gradually change from a cross-steep ladder to two nearly straight parallel lines. With time increases, the microstructure of Ti-rich Ti/Ni composites treated at 720℃ transforming from a regular layered structure to a mixture structure with alternating TiNi and Ti2Ni layers. When the hold time is less than 10h, the structure of TiNi phase is composed of B19" with complex monoclinal structure and B2 with CsCl structure, while when the time is more than 10h, only B19" phase exists. In the process of cooling/heating, a good martensitic and reversible phase transition of A→M/M→A occurred in each sample. With the increase of time, the phase transition hysteresis (Ap-Mp) from 22.4 ℃ of the 1 h heat treatment sample increases to 31.9 ℃ of the 30 h sample.
2020, 49(9):3163-3169.
DOI: 10.12442/j.issn.1002-185X.20190695
Abstract:
Ta2O5 nanorod films doped with Cu2+ were prepared by a two-step hydrothermal method on tantalum. XRD, SEM and XPS were used to analyze the phase and surface microstructure of the materials. The ion precipitation concentration of samples in normal saline was detected by ICP, and the antibacterial ability of Ta2O5 films with different content of copper was tested by plate counting method. The results showed that Ta2O5 nanorods with simple rhombic crystal structure were generated on the tantalum surface by two-step hydrothermal treatment, and the doping of Cu2+ did not significantly affect the microstructure and phase of nanorods. With the increase of time, the precipitation rate of copper ions in copper-doped films gradually tends to be flat. The result of plate counting showed that when the doping amount of Cu2+ reached 2.68At%, copper doped Ta2O5 nanorod films had the best antibacterial performance and the antibacterial rate reached 99.2%.
Ta2O5 nanorod films doped with Cu2+ were prepared by a two-step hydrothermal method on tantalum. XRD, SEM and XPS were used to analyze the phase and surface microstructure of the materials. The ion precipitation concentration of samples in normal saline was detected by ICP, and the antibacterial ability of Ta2O5 films with different content of copper was tested by plate counting method. The results showed that Ta2O5 nanorods with simple rhombic crystal structure were generated on the tantalum surface by two-step hydrothermal treatment, and the doping of Cu2+ did not significantly affect the microstructure and phase of nanorods. With the increase of time, the precipitation rate of copper ions in copper-doped films gradually tends to be flat. The result of plate counting showed that when the doping amount of Cu2+ reached 2.68At%, copper doped Ta2O5 nanorod films had the best antibacterial performance and the antibacterial rate reached 99.2%.
2020, 49(9):3170-3176.
DOI: 10.12442/j.issn.1002-185X.20190702
Abstract:
Severe plastic deformation can be achieved in the sample via cyclic channel die compression (CCDC) without changing its shape and size. The height/width ratio is one of the important parameters that affect the CCDC process. A finite element method and experimental validation are employed to investigate the effect of height/width ratio of the sample on compression process, microstructure and properties in this study. The results show that the effective strain is inhomogeneous after deformation. The larger the height/width ratio is, the larger the average effective strain for a single pass compression, and the higher the effective stress. After one pass, grains are squashed, and more serious as the height/width ratio increases. After 3 passes, a large number of shear bands are formed, and become narrow with the increase of height/width ratio. After 12 passes, more equiaxed and finer grains are obtained in the sample with height/width ratio of 2. Hardness of pure copper increases significantly after CCDC, and the hardness value of the sample is higher with height/width ratio of 2.
Severe plastic deformation can be achieved in the sample via cyclic channel die compression (CCDC) without changing its shape and size. The height/width ratio is one of the important parameters that affect the CCDC process. A finite element method and experimental validation are employed to investigate the effect of height/width ratio of the sample on compression process, microstructure and properties in this study. The results show that the effective strain is inhomogeneous after deformation. The larger the height/width ratio is, the larger the average effective strain for a single pass compression, and the higher the effective stress. After one pass, grains are squashed, and more serious as the height/width ratio increases. After 3 passes, a large number of shear bands are formed, and become narrow with the increase of height/width ratio. After 12 passes, more equiaxed and finer grains are obtained in the sample with height/width ratio of 2. Hardness of pure copper increases significantly after CCDC, and the hardness value of the sample is higher with height/width ratio of 2.
2020, 49(9):3177-3181.
DOI: 10.12442/j.issn.1002-185X.20191113
Abstract:
The new Nb3Sn superconducting magnet system for the fourth-generation 45GHz ECR source(FECR) is under developing in the institute of Modern Physics (IMP). Because the magnet is made from Nb3Sn which is sensitive to the strain and there are strong Lorentz forces between the solenoids and sextupole coils, the mechanical structure design is a big challenge. In order to validity the reasonability and feasibility of the structure design and its simulation results, a half-length prototype of the FECR magnet was developed.This paper presents the detailed design of the magnet structure. The stress distribution and variation of the prototype during assembly,cooling down and charging have been got with the three-dimensional finite-element model and are presented in the paper. The results will be used as reference of the room-temperature magnet assembly.
The new Nb3Sn superconducting magnet system for the fourth-generation 45GHz ECR source(FECR) is under developing in the institute of Modern Physics (IMP). Because the magnet is made from Nb3Sn which is sensitive to the strain and there are strong Lorentz forces between the solenoids and sextupole coils, the mechanical structure design is a big challenge. In order to validity the reasonability and feasibility of the structure design and its simulation results, a half-length prototype of the FECR magnet was developed.This paper presents the detailed design of the magnet structure. The stress distribution and variation of the prototype during assembly,cooling down and charging have been got with the three-dimensional finite-element model and are presented in the paper. The results will be used as reference of the room-temperature magnet assembly.
2020, 49(9):3182-3188.
DOI: 10.12442/j.issn.1002-185X.20200242
Abstract:
High density GH3536 ni-based superalloy block specimens were prepared by laser selective melting method, and the microstructure and crystal orientation of GH3536 alloy were analyzed. The results show that with the increase of laser energy density, the density of the formed sampleSincreasedSatSfirstSandSthenSdecreased, When the laser energy density is 180~230J.m-1, the density reaches over 99.55%. The structure has obvious anisotropy, the microstructure perpendicular to the construction direction presented a checkerboard morphology, and most of the grains were equiaxed (the length-diameter ratio was 1.828μm) and were refined (dmean=11.226μm), In particular, the grain size in the lap area of molten pool is finer (less than 5 m). Parallel to the construction direction was the fish scale morphology, most of which were columnar crystals (the length-diameter ratio was 2.831μm), with a larger grain diameter (dmean=25.964μm). Simultaneously, SLM processed GH3536 nickel-based superalloy has obvious preferential orientation. On the cross section, the grain has a strong orientation < 100 > orientation, which is cubic texture {100}<001> perpendicular to and parallel to the construction direction. In addition, grain growth in SLM solidification has a significant effect on the evolution of crystal orientation in grain, the crystal orientation in the deformed grain of the longitudinal section does not change obviously, while the crystal orientation in the deformed grain of the longitudinal section changes obviously, this is due to the extremely high temperature gradient and rapid cooling rate (105K/s) of SLM.
High density GH3536 ni-based superalloy block specimens were prepared by laser selective melting method, and the microstructure and crystal orientation of GH3536 alloy were analyzed. The results show that with the increase of laser energy density, the density of the formed sampleSincreasedSatSfirstSandSthenSdecreased, When the laser energy density is 180~230J.m-1, the density reaches over 99.55%. The structure has obvious anisotropy, the microstructure perpendicular to the construction direction presented a checkerboard morphology, and most of the grains were equiaxed (the length-diameter ratio was 1.828μm) and were refined (dmean=11.226μm), In particular, the grain size in the lap area of molten pool is finer (less than 5 m). Parallel to the construction direction was the fish scale morphology, most of which were columnar crystals (the length-diameter ratio was 2.831μm), with a larger grain diameter (dmean=25.964μm). Simultaneously, SLM processed GH3536 nickel-based superalloy has obvious preferential orientation. On the cross section, the grain has a strong orientation < 100 > orientation, which is cubic texture {100}<001> perpendicular to and parallel to the construction direction. In addition, grain growth in SLM solidification has a significant effect on the evolution of crystal orientation in grain, the crystal orientation in the deformed grain of the longitudinal section does not change obviously, while the crystal orientation in the deformed grain of the longitudinal section changes obviously, this is due to the extremely high temperature gradient and rapid cooling rate (105K/s) of SLM.
2020, 49(9):3189-3194.
DOI: 10.12442/j.issn.1002-185X.20200020
Abstract:
The TiAl-based alloy has excellent high-temperature comprehensive properties such as low density, high specific strength and high specific stiffness. It is expected to replace a nickel-based alloy with high density in aero-engine manufacturing. In this paper, the transformation rule of β2-phase and its effect on the mechanical properties at room temperature in the cast TiAl alloy were studied systematically. The experimental results demonstrated that the toughness of the cast Ti-Al-Nb-Cr-Mo-B alloy is not decreased when the holding time is 2h, but the strength increased from 1200MPa to 1500 MPa. In the process of heat preservation, α decomposes into γ + β phase, and then in the process of cooling, the disordered β phase transforms into ordered β2 phase. The experimental results show thatβ2 phase is a hard brittle phase, and a small amount of β2 phase can promote the strength of the alloy.
The TiAl-based alloy has excellent high-temperature comprehensive properties such as low density, high specific strength and high specific stiffness. It is expected to replace a nickel-based alloy with high density in aero-engine manufacturing. In this paper, the transformation rule of β2-phase and its effect on the mechanical properties at room temperature in the cast TiAl alloy were studied systematically. The experimental results demonstrated that the toughness of the cast Ti-Al-Nb-Cr-Mo-B alloy is not decreased when the holding time is 2h, but the strength increased from 1200MPa to 1500 MPa. In the process of heat preservation, α decomposes into γ + β phase, and then in the process of cooling, the disordered β phase transforms into ordered β2 phase. The experimental results show thatβ2 phase is a hard brittle phase, and a small amount of β2 phase can promote the strength of the alloy.
Zehui Yang
,
Nan Wang
,
Yongnan Chen
,
Long Zhang
,
Hong Chen
,
Jianmin Hao
,
Yongqing Zhao
,
Chenxing Shi
,
Wenlong Shi
2020, 49(9):3195-3202.
DOI: 10.12442/j.issn.1002-185X.20190703
Abstract:
The design and preparation of antifriction coating on titanium alloy surface is one of the important technologies to improve the wear resistance of titanium alloy components and ensure the safety in service. In order to solve the problems of uneven dispersion of antifriction agents and poor adhesion of coating caused by easy agglomeration in titanium alloy antifriction coating, this paper adopts one-step micro-arc oxidation technology to generate MoS2/TiO2 composite ceramic coating with anti-wear effect on the surface of titanium alloy in situ. The effects of sulfur source concentration on microstructure and wear resistance of the coating was discussed. The results showed that MoS2/TiO2 composite ceramic film was successfully prepared by micro-arc oxidation with Na2S and Na2MoO4 as sulfur source and molybdenum source respectively. By controlling Na2S concentration, nano-MoS2 particles with small size and uniform distribution can be generated in situ, and the content and morphology of MoS2 can be regulated. With the increase of Na2S concentration, the coating becomes compact and the roughness decrease. When the addition amount reached 60g/L, the coating turn into loose due to sulfur precipitation and the roughness increased. Due to the uniform distribution of MoS2 particles on the surface and inside of the coating, the abrasion resistance of the obtained coating improved by 395.4% and 129.4% respectively compared with the conventional micro-arc oxidation coating or the coating prepared by directly adding MoS2 particles into the electrolyte. At the same time, adhesion (reaching 723.8N) increased by 87.1% compared with traditional micro-arc oxidation, indicating that this technology not only guarantees good self-lubrication effect, but also improves adhesion of coating and matrix. The results can provide new ideas and research methods for the design and preparation of titanium alloy wear-resistant coatings.
The design and preparation of antifriction coating on titanium alloy surface is one of the important technologies to improve the wear resistance of titanium alloy components and ensure the safety in service. In order to solve the problems of uneven dispersion of antifriction agents and poor adhesion of coating caused by easy agglomeration in titanium alloy antifriction coating, this paper adopts one-step micro-arc oxidation technology to generate MoS2/TiO2 composite ceramic coating with anti-wear effect on the surface of titanium alloy in situ. The effects of sulfur source concentration on microstructure and wear resistance of the coating was discussed. The results showed that MoS2/TiO2 composite ceramic film was successfully prepared by micro-arc oxidation with Na2S and Na2MoO4 as sulfur source and molybdenum source respectively. By controlling Na2S concentration, nano-MoS2 particles with small size and uniform distribution can be generated in situ, and the content and morphology of MoS2 can be regulated. With the increase of Na2S concentration, the coating becomes compact and the roughness decrease. When the addition amount reached 60g/L, the coating turn into loose due to sulfur precipitation and the roughness increased. Due to the uniform distribution of MoS2 particles on the surface and inside of the coating, the abrasion resistance of the obtained coating improved by 395.4% and 129.4% respectively compared with the conventional micro-arc oxidation coating or the coating prepared by directly adding MoS2 particles into the electrolyte. At the same time, adhesion (reaching 723.8N) increased by 87.1% compared with traditional micro-arc oxidation, indicating that this technology not only guarantees good self-lubrication effect, but also improves adhesion of coating and matrix. The results can provide new ideas and research methods for the design and preparation of titanium alloy wear-resistant coatings.
2020, 49(9):3203-3208.
DOI: 10.12442/j.issn.1002-185X.20190704
Abstract:
Quasi-static uniaxial compression on closed-cell aluminum foam and compression on closed-cell aluminum foam with lateral constraint were performed to study the size effects. The effects of sizes (height and diameter) and density of foam specimen on the mechanical properties of aluminum foam were investigated. The results showed that, the mechanical properties of closed-cell aluminum foams under uniaxial compression have obvious size effects, while the size effects in closed -cell aluminum foams with lateral constraint is not so obvious. Foam density is critical to the mechanical properties of closed-cell aluminum foams under the two different loading conditions. The dependency of yield strength and plateau stress of aluminum foam with lateral constraint on foam density is found to be more significant.
Quasi-static uniaxial compression on closed-cell aluminum foam and compression on closed-cell aluminum foam with lateral constraint were performed to study the size effects. The effects of sizes (height and diameter) and density of foam specimen on the mechanical properties of aluminum foam were investigated. The results showed that, the mechanical properties of closed-cell aluminum foams under uniaxial compression have obvious size effects, while the size effects in closed -cell aluminum foams with lateral constraint is not so obvious. Foam density is critical to the mechanical properties of closed-cell aluminum foams under the two different loading conditions. The dependency of yield strength and plateau stress of aluminum foam with lateral constraint on foam density is found to be more significant.
2020, 49(9):3209-3217.
DOI: 10.12442/j.issn.1002-185X.20190725
Abstract:
Ni-(50-x)Al-xSc (at%) alloys were prepared by using vacuum arc smelting furnace with a water-cooled copper mold. The microstructures of the alloys were observed by optical microscope and scanning electron microscope (SEM). The phases of the alloys were analyzed by X-ray diffraction (XRD) and energy spectrum (EDS). The solidification processes of the alloys were analyzed based on scanning calorimetry (DSC) analyzing results. The mechanical properties of the alloys were analyzed by micro Vickers hardness test and nanoindentation test. With the two-phase system simplified model, the overall elastic moduli of the alloys were estimated. The results show that the sub-rapid solidification structures of Ni-50Al, Ni-45Al-5Sc, Ni-40Al-10Sc and Ni-35Al-15Sc alloys are NiAl, NiAl+AlNi2Sc, NiAl+AlNi2Sc and NiAl+AlNi2Sc+(AlNi2Sc+Ni-16.93Al-21.53Sc), respectively. The precipitation ordered of each phase in the alloys are in the ordered of NiAl, AlNi2Sc and (AlNi2Sc+Ni-16.93Al-21.53Sc) accordingly. The value of crystal growth Jackson factor of AlNi2Sc compound was α = 0.2, which is much smaller than 2, which means AlNi2Sc phase growths in a continuous manner and a coarse solid/liquid interface. The hardness of the primary NiAl phase is increased by alloying with Sc element and the hardness of the secondary phase AlNi2Sc is greater than the primary NiAl phase. Therefore, the hardnesses of the Ni-(50-x)Al-xSc alloys increased. Alloying with Sc can reduce the elastic modulus of the primary NiAl phase, and the overall elastic moduli of Ni-(50-x)Al-xSc alloys decrease compared with that of the NiAl intermetallic compound.
Ni-(50-x)Al-xSc (at%) alloys were prepared by using vacuum arc smelting furnace with a water-cooled copper mold. The microstructures of the alloys were observed by optical microscope and scanning electron microscope (SEM). The phases of the alloys were analyzed by X-ray diffraction (XRD) and energy spectrum (EDS). The solidification processes of the alloys were analyzed based on scanning calorimetry (DSC) analyzing results. The mechanical properties of the alloys were analyzed by micro Vickers hardness test and nanoindentation test. With the two-phase system simplified model, the overall elastic moduli of the alloys were estimated. The results show that the sub-rapid solidification structures of Ni-50Al, Ni-45Al-5Sc, Ni-40Al-10Sc and Ni-35Al-15Sc alloys are NiAl, NiAl+AlNi2Sc, NiAl+AlNi2Sc and NiAl+AlNi2Sc+(AlNi2Sc+Ni-16.93Al-21.53Sc), respectively. The precipitation ordered of each phase in the alloys are in the ordered of NiAl, AlNi2Sc and (AlNi2Sc+Ni-16.93Al-21.53Sc) accordingly. The value of crystal growth Jackson factor of AlNi2Sc compound was α = 0.2, which is much smaller than 2, which means AlNi2Sc phase growths in a continuous manner and a coarse solid/liquid interface. The hardness of the primary NiAl phase is increased by alloying with Sc element and the hardness of the secondary phase AlNi2Sc is greater than the primary NiAl phase. Therefore, the hardnesses of the Ni-(50-x)Al-xSc alloys increased. Alloying with Sc can reduce the elastic modulus of the primary NiAl phase, and the overall elastic moduli of Ni-(50-x)Al-xSc alloys decrease compared with that of the NiAl intermetallic compound.
2020, 49(9):3218-3224.
DOI: 10.12442/j.issn.1002-185X.20190751
Abstract:
The properties of pre-alloyed powder have an important influence on the additive manufacturing process, especially for Ti-Ni alloys with special shape memory effects. However, there are limited reports on the studies for the variation of Ti-Ni pre-alloyed powder with heat treatment temperatures and number of thermal cycles. In this work, the phase transformation behavior, microstructure and phase composition of 53~106μm Ti-Ni pre-alloyed powder used for electron beam melting (EBM) were studied using the differential scanning calorimeter, X-ray diffraction, scanning electron microscope. The results showed that the powder had good particle size distribution, internal filling and spherical topography, and suitable for EBM process. The structure and composition became uniform, internal stress and dislocation were eliminated and crystal grain size grown with the increase of heat treatment temperature, which caused the original multi-step phase transformation to one-step phase transformation during the heating and cooling process after 550 °C and the phase transformation points maintains a stable state after 650 °C. The phase composition not changed during the heat treatment process and the powder had best sintered state under 750 °C. The phase composition, one-step phase transformation behavior and phase transformation points were all not changed for the powder during 750 °C thermal cycles test, showed good thermal cycling stability. Ti-Ni solid samples with good surface condition were successfully prepared using EBM under 750 °C preheating temperature for bottom plate and powder layer.
The properties of pre-alloyed powder have an important influence on the additive manufacturing process, especially for Ti-Ni alloys with special shape memory effects. However, there are limited reports on the studies for the variation of Ti-Ni pre-alloyed powder with heat treatment temperatures and number of thermal cycles. In this work, the phase transformation behavior, microstructure and phase composition of 53~106μm Ti-Ni pre-alloyed powder used for electron beam melting (EBM) were studied using the differential scanning calorimeter, X-ray diffraction, scanning electron microscope. The results showed that the powder had good particle size distribution, internal filling and spherical topography, and suitable for EBM process. The structure and composition became uniform, internal stress and dislocation were eliminated and crystal grain size grown with the increase of heat treatment temperature, which caused the original multi-step phase transformation to one-step phase transformation during the heating and cooling process after 550 °C and the phase transformation points maintains a stable state after 650 °C. The phase composition not changed during the heat treatment process and the powder had best sintered state under 750 °C. The phase composition, one-step phase transformation behavior and phase transformation points were all not changed for the powder during 750 °C thermal cycles test, showed good thermal cycling stability. Ti-Ni solid samples with good surface condition were successfully prepared using EBM under 750 °C preheating temperature for bottom plate and powder layer.
2020, 49(9):3225-3234.
DOI: 10.12442/j.issn.1002-185X.20190742
Abstract:
FeAlMoCrC and FeAlNiMoCrC coatings were prepared by spraying two kinds of self-developed wire onto the surface of 45 steel with high velocity arc spraying technology. The microstructure of the two coatings was analyzed and the cyclic oxidation behavior of the two coatings and substrate at 700 ℃ was investigated. The results show that the FeAlMoCrC coating mainly consists of three intermetallic compounds: FeAl, FeCr, and Fe2AlV, and two oxide phases of Al2O3 and Fe3O4. The FeAlNiMoCrC coating is mainly composed of four intermetallic compounds: AlNi, AlCr2, FeNi3 and Fe8Cr, and three oxide phases of Al2O3, Cr2O3 and Fe3O4. According to the calculation of the porosity of the coating, it is found that the internal porosity of the coating is low, all of which are less than 10%. After fitting and analyzing the oxidation weight gain curve, it is found that the FeAlNiMoCrC coating has lower oxidation rate constant, larger oxidation index, slower oxidation rate and better oxidation resistance. Through phase and microstructure analyzing, it is considered that the low porosity of the coating and the formation of continuous and dense oxide films such as Al2O3, Cr2O3 and Fe3O4 in the oxidation products contribute to the improvement of high temperature oxidation resistance.
FeAlMoCrC and FeAlNiMoCrC coatings were prepared by spraying two kinds of self-developed wire onto the surface of 45 steel with high velocity arc spraying technology. The microstructure of the two coatings was analyzed and the cyclic oxidation behavior of the two coatings and substrate at 700 ℃ was investigated. The results show that the FeAlMoCrC coating mainly consists of three intermetallic compounds: FeAl, FeCr, and Fe2AlV, and two oxide phases of Al2O3 and Fe3O4. The FeAlNiMoCrC coating is mainly composed of four intermetallic compounds: AlNi, AlCr2, FeNi3 and Fe8Cr, and three oxide phases of Al2O3, Cr2O3 and Fe3O4. According to the calculation of the porosity of the coating, it is found that the internal porosity of the coating is low, all of which are less than 10%. After fitting and analyzing the oxidation weight gain curve, it is found that the FeAlNiMoCrC coating has lower oxidation rate constant, larger oxidation index, slower oxidation rate and better oxidation resistance. Through phase and microstructure analyzing, it is considered that the low porosity of the coating and the formation of continuous and dense oxide films such as Al2O3, Cr2O3 and Fe3O4 in the oxidation products contribute to the improvement of high temperature oxidation resistance.
2020, 49(9):3235-3243.
DOI: 10.12442/j.issn.1002-185X.20190762
Abstract:
The low cycle fatigue properties with Stress and Strain constant-ampitude controlled test methods，the tensile properties at 650℃, the microstructure at different positions and the fatigue fracture of an FGH97 superalloy disc, which was manufactured by Argon Atomization (AA) + Hot Isostatic Pressing (HIP)+Heat Treatment process, were investigated. The results reveal that the grains size and the γ′ weresimilar at different positions. The tensile strengthes at 650℃ were between 1325 to 1340MPa, and the Yield Strengthes were between 1010 to 1025MPa, which are relatively stable. The average Nf by Stress-controled was 200000 cycles at different positions, Weibull distribution η was 215194.The effect of the inclusion size of less than 80μm on Nf was not obvious. The Weibull distribution η of the Strain-controled was 14622 when the Nf was less than 20000 cycles, and 44342 when Nf was more than 20000 cycles. The variation of inclusion area leads to the difference of characteristic value beta of Nf Weibull distribution. The crack source of fatigue fracture was mainly the inclusions, and the fracture morphologies were rather similar. The fatigue by the strain controled test was more sensitive to the inclusions.
The low cycle fatigue properties with Stress and Strain constant-ampitude controlled test methods，the tensile properties at 650℃, the microstructure at different positions and the fatigue fracture of an FGH97 superalloy disc, which was manufactured by Argon Atomization (AA) + Hot Isostatic Pressing (HIP)+Heat Treatment process, were investigated. The results reveal that the grains size and the γ′ weresimilar at different positions. The tensile strengthes at 650℃ were between 1325 to 1340MPa, and the Yield Strengthes were between 1010 to 1025MPa, which are relatively stable. The average Nf by Stress-controled was 200000 cycles at different positions, Weibull distribution η was 215194.The effect of the inclusion size of less than 80μm on Nf was not obvious. The Weibull distribution η of the Strain-controled was 14622 when the Nf was less than 20000 cycles, and 44342 when Nf was more than 20000 cycles. The variation of inclusion area leads to the difference of characteristic value beta of Nf Weibull distribution. The crack source of fatigue fracture was mainly the inclusions, and the fracture morphologies were rather similar. The fatigue by the strain controled test was more sensitive to the inclusions.
2020, 49(9):3244-3250.
DOI: 10.12442/j.issn.1002-185X.20190774
Abstract:
A new sandwich core called lotus seedpod-like core is proposed in this paper. High temperature creep forming experiment was conducted on TC4 titanium plate to prove the feasibility of lotus seedpod-like core. Moreover, effects of major forming parameters on the height, microstructure, mechanical properties of the lotus seedpod-like core were studied. The results show that it is feasible to prepare lotus seedpod-like core by high temperature creep forming. During creep forming, TC4 titanium sheet transformed to lotus seedpod-like core by dislocation motion and grain boundary sliding. After high temperature creep, the fine equiaxed structure completely transformed into the recrystallized equiaxed structure. The height, compressive strength and specific compressive strength of core are increased with the increase of forming pressure and holding time.
A new sandwich core called lotus seedpod-like core is proposed in this paper. High temperature creep forming experiment was conducted on TC4 titanium plate to prove the feasibility of lotus seedpod-like core. Moreover, effects of major forming parameters on the height, microstructure, mechanical properties of the lotus seedpod-like core were studied. The results show that it is feasible to prepare lotus seedpod-like core by high temperature creep forming. During creep forming, TC4 titanium sheet transformed to lotus seedpod-like core by dislocation motion and grain boundary sliding. After high temperature creep, the fine equiaxed structure completely transformed into the recrystallized equiaxed structure. The height, compressive strength and specific compressive strength of core are increased with the increase of forming pressure and holding time.
2020, 49(9):3251-3259.
DOI: 10.12442/j.issn.1002-185X.20190782
Abstract:
New Al-4.5Cu-1Li-0.7Mg-1Zn-0.3Ag-0.3Mn-0.2Zr aluminium lithium alloys were prepared by casting and hot formation. The effects of cold-rolled pre-deformation on microstructure and mechanical properties after solid solution were investigated using Vickers hardness, tensile testing, scanning electron microscopy and transmission electron microscopy. The results show that cold-rolled pre-deformation can effectively promote the precipitation of T1 phases and reduce the volume fraction of θ" phases in the matrix. Adding cold-rolled pre-deformation resulted in an enhanced age hardening response and shorter the time to reach peak aging. At the same time, the grain boundary precipitates change from continuous precipitation to discontinuous precipitation, and the width of the PFZs becomes smaller. The yield strength, tensile strength and elongation of as-aged alloy, when the pre-deformation amount was 15%, were 668 MPa, 690 MPa and 7.9%, respectively.
New Al-4.5Cu-1Li-0.7Mg-1Zn-0.3Ag-0.3Mn-0.2Zr aluminium lithium alloys were prepared by casting and hot formation. The effects of cold-rolled pre-deformation on microstructure and mechanical properties after solid solution were investigated using Vickers hardness, tensile testing, scanning electron microscopy and transmission electron microscopy. The results show that cold-rolled pre-deformation can effectively promote the precipitation of T1 phases and reduce the volume fraction of θ" phases in the matrix. Adding cold-rolled pre-deformation resulted in an enhanced age hardening response and shorter the time to reach peak aging. At the same time, the grain boundary precipitates change from continuous precipitation to discontinuous precipitation, and the width of the PFZs becomes smaller. The yield strength, tensile strength and elongation of as-aged alloy, when the pre-deformation amount was 15%, were 668 MPa, 690 MPa and 7.9%, respectively.
2020, 49(9):3260-3264.
DOI: 10.12442/j.issn.1002-185X.20200071
Abstract:
Al2O3/Al-10Si composites were prepared by high pressure solidification at 3, 4, 5 GPa, and then heat treated at 160 °C for 2, 4, and 6 h. Thermal stability of microstructure and mechanical properties of Al2O3/Al-10Si composites under high pressure were systematically studied. The results showed that heat treatment leads to the precipitation of Si particles due to the supersaturation in α phase.The precipitation of Si leads to a decrease of supersaturation. The compression strength and ration shows a slight increase after heat treatment due to the combination of precipitation strengthening and solid solution strengthening. At 160℃/4h, Al2O3/Al-10Si composites showed the best mechanical properties. After solidified under 5GPa and heat treatment at 160℃/4h, Al2O3/Al-10Si composites got the maximum compressive strength which is about 716MPa.
Al2O3/Al-10Si composites were prepared by high pressure solidification at 3, 4, 5 GPa, and then heat treated at 160 °C for 2, 4, and 6 h. Thermal stability of microstructure and mechanical properties of Al2O3/Al-10Si composites under high pressure were systematically studied. The results showed that heat treatment leads to the precipitation of Si particles due to the supersaturation in α phase.The precipitation of Si leads to a decrease of supersaturation. The compression strength and ration shows a slight increase after heat treatment due to the combination of precipitation strengthening and solid solution strengthening. At 160℃/4h, Al2O3/Al-10Si composites showed the best mechanical properties. After solidified under 5GPa and heat treatment at 160℃/4h, Al2O3/Al-10Si composites got the maximum compressive strength which is about 716MPa.
2020, 49(9):3265-3272.
DOI: 10.12442/j.issn.1002-185X.20190787
Abstract:
The rolling speed is the key process parameter in the three-roll cold rolling forming process, which determines its mechanical characteristics and temperature rise. Based on this phenomenon, this paper takes cold-rolled AZ31 magnesium alloy tubes as the research object, by numerical simulation, compares and analyzes the influence of different rolling speeds on the equivalent stress, equivalent plastic strain and joint temperature of each characteristic deformation section. The results show that these parameters increased with the increase of rolling speed. By means of the cellular automaton model and experiment, the preliminary evolution law of continuous recrystallization and refinement of the grain during the rolling process was proved. The comparative analysis experiment and simulation results were combined with various factors to obtain 800mm/s. The rolling speed can better meet the requirements of the process requirements, which provides a basis for the selection of rolling speed of cold-rolled magnesium alloy tubes.
The rolling speed is the key process parameter in the three-roll cold rolling forming process, which determines its mechanical characteristics and temperature rise. Based on this phenomenon, this paper takes cold-rolled AZ31 magnesium alloy tubes as the research object, by numerical simulation, compares and analyzes the influence of different rolling speeds on the equivalent stress, equivalent plastic strain and joint temperature of each characteristic deformation section. The results show that these parameters increased with the increase of rolling speed. By means of the cellular automaton model and experiment, the preliminary evolution law of continuous recrystallization and refinement of the grain during the rolling process was proved. The comparative analysis experiment and simulation results were combined with various factors to obtain 800mm/s. The rolling speed can better meet the requirements of the process requirements, which provides a basis for the selection of rolling speed of cold-rolled magnesium alloy tubes.
2020, 49(9):3273-3284.
DOI: 10.12442/j.issn.1002-185X.20190732
Abstract:
In recent years, the researches on the mechanical behavior of high-entropy alloys with cubic structure at cryogenic temperature (77K) have become a hot topic. It is found that stacking fault energy (SFE) of some cubic high-entropy alloys decreases with the decrease of temperature. Compared with that at room temperature, the mechanical properties of these alloys at cryogenic temperature show remarkable increase, suggesting their tremendous potential as promising structural materials used at cryogenic-temperature. In this paper, recent progress on the mechanical behavior of high-entropy alloys with cubic structure at cryogenic temperature are reviewed systematically, focusing on the underlying mechanisms of strengthening and toughening during plastic deformation. At last, the possible future development trend is also given.
In recent years, the researches on the mechanical behavior of high-entropy alloys with cubic structure at cryogenic temperature (77K) have become a hot topic. It is found that stacking fault energy (SFE) of some cubic high-entropy alloys decreases with the decrease of temperature. Compared with that at room temperature, the mechanical properties of these alloys at cryogenic temperature show remarkable increase, suggesting their tremendous potential as promising structural materials used at cryogenic-temperature. In this paper, recent progress on the mechanical behavior of high-entropy alloys with cubic structure at cryogenic temperature are reviewed systematically, focusing on the underlying mechanisms of strengthening and toughening during plastic deformation. At last, the possible future development trend is also given.
