Volume 41,Issue 6,2012 Table of Contents
2012, 41(6):941-946.
Abstract:
Ultrafine-grained (UFG) metal materials processed by severe plastic deformation (SPD) have attracted the great interest. This overview introduces some attractive SPD techniques. Special attention is paid to two new deformation techniques named Elliptical Cross-section Spiral Channel Extrusion with Equal-area (ECSEE) and Elliptical Cross-section Spiral Channel Drawing with Equal-area (ECSDE). The mechanism and microstructure transformation characteristics of materials in SPD, current problems and ongoing research are also discussed in detail
Ultrafine-grained (UFG) metal materials processed by severe plastic deformation (SPD) have attracted the great interest. This overview introduces some attractive SPD techniques. Special attention is paid to two new deformation techniques named Elliptical Cross-section Spiral Channel Extrusion with Equal-area (ECSEE) and Elliptical Cross-section Spiral Channel Drawing with Equal-area (ECSDE). The mechanism and microstructure transformation characteristics of materials in SPD, current problems and ongoing research are also discussed in detail
2012, 41(6):947-951.
Abstract:
Nickel is widely used as a bleaching element in white gold alloys for jewelry, it helps to obtain good color and mechanical properties. Although master alloy suppliers promise the safety of their products, the nickel allergy cases caused by such white gold jewelries are reported now and then. The purpose of this study is to investigate nickel release rate of a so-called “No nickel allergy” 10 K white gold alloy extensively used for jewelry and its potential risk to cause nickel allergy. The samples were processed by different heat treatment conditions and surface treatment methods, their nickel release rate were tested according to EN1811 standard. The results show that nickel release rate is closely related to the corrosion resistance and changes under different processing conditions even for the same material. The nickel release rate sequence (from big to little) is as follows: “annealing at the two-phase region with rough surface > cold working with rough surface > cold working with polishing surface > quenching with rough surface > quenching plus low temperature tempering with rough surface”. Although the adjusted values of nickel release rate under various process conditions met the requirement in nickel Directive “94/27/EC”, most of them fail to meet the requirement specified in “2004/96/EC” for piercing jewelry, and the actual values obviously markedly exceed both Directives. There would exist nickel allergy risk for jewelries made from this material, especially for puncture accessories
Nickel is widely used as a bleaching element in white gold alloys for jewelry, it helps to obtain good color and mechanical properties. Although master alloy suppliers promise the safety of their products, the nickel allergy cases caused by such white gold jewelries are reported now and then. The purpose of this study is to investigate nickel release rate of a so-called “No nickel allergy” 10 K white gold alloy extensively used for jewelry and its potential risk to cause nickel allergy. The samples were processed by different heat treatment conditions and surface treatment methods, their nickel release rate were tested according to EN1811 standard. The results show that nickel release rate is closely related to the corrosion resistance and changes under different processing conditions even for the same material. The nickel release rate sequence (from big to little) is as follows: “annealing at the two-phase region with rough surface > cold working with rough surface > cold working with polishing surface > quenching with rough surface > quenching plus low temperature tempering with rough surface”. Although the adjusted values of nickel release rate under various process conditions met the requirement in nickel Directive “94/27/EC”, most of them fail to meet the requirement specified in “2004/96/EC” for piercing jewelry, and the actual values obviously markedly exceed both Directives. There would exist nickel allergy risk for jewelries made from this material, especially for puncture accessories
3 Analysis of Mechanical Parameters during Hot Continuous Rolling Process of Titanium Alloy TC11 Rod
2012, 41(6):952-957.
Abstract:
Titanium alloy TC11 rods with Ф25 mm, were rolled to that with Ф17 mm in four passes by a triangle-round-triangle-round sequence. The rod temperature drop was measured at entry temperature 950 °C during continuous rolling, and the rolling forces and the roll torques were measured in the case of different area reductions at 750, 850, 950, and 1050 °C. Then, the geometry shapes of deformation zone were analyzed for different passes. The mathematic model of the rolling force for Y-type mill was modified based on empirical modifications of two-roll theories. A number of experiments were also carried out to check the validity of the proposed mathematic model. The result shows that the difference between the calculated value and the experimental value is relatively minor. Therefore, this mathematic model can provide the foundation for theoretical research and engineering application of Y-type rolling process
Titanium alloy TC11 rods with Ф25 mm, were rolled to that with Ф17 mm in four passes by a triangle-round-triangle-round sequence. The rod temperature drop was measured at entry temperature 950 °C during continuous rolling, and the rolling forces and the roll torques were measured in the case of different area reductions at 750, 850, 950, and 1050 °C. Then, the geometry shapes of deformation zone were analyzed for different passes. The mathematic model of the rolling force for Y-type mill was modified based on empirical modifications of two-roll theories. A number of experiments were also carried out to check the validity of the proposed mathematic model. The result shows that the difference between the calculated value and the experimental value is relatively minor. Therefore, this mathematic model can provide the foundation for theoretical research and engineering application of Y-type rolling process
2012, 41(6):958-961.
Abstract:
The as-extruded X20 magnesium alloys containing 2.0wt% Ca were solution-treated at 410 oC for 20 h. The microstructures before and after solution treatment were observed by optical microscope (OM), scanning electron microscope (SEM) together with an energy dispersive spectroscope (EDS), and transmission electron microscope (TEM). The phase compositions before and after solution treatment were confirmed by X-ray diffraction (XRD). The results show that the amount of β-Mg17Al12 phases decreases remarkably after solution treatment, and new Al2Ca phases are formed. The formation of Al2Ca phase might be due to high concentration of Ca atoms in residual β-Mg17Al12 phases, which leads the place of Mg atoms to be substituted by Ca. On the other hand, Al2Ca phase could be also described as a completing product between Al-Ca system and Mg-Ca system intermetallics due to its high structural stability
The as-extruded X20 magnesium alloys containing 2.0wt% Ca were solution-treated at 410 oC for 20 h. The microstructures before and after solution treatment were observed by optical microscope (OM), scanning electron microscope (SEM) together with an energy dispersive spectroscope (EDS), and transmission electron microscope (TEM). The phase compositions before and after solution treatment were confirmed by X-ray diffraction (XRD). The results show that the amount of β-Mg17Al12 phases decreases remarkably after solution treatment, and new Al2Ca phases are formed. The formation of Al2Ca phase might be due to high concentration of Ca atoms in residual β-Mg17Al12 phases, which leads the place of Mg atoms to be substituted by Ca. On the other hand, Al2Ca phase could be also described as a completing product between Al-Ca system and Mg-Ca system intermetallics due to its high structural stability
2012, 41(6):962-966.
Abstract:
The slabs of the second generation single crystal superalloy DD6 were cast using bi-seeded crystals with symmetric twist low angle grain boundaries. The influence of low angle boundary (LAB) on the stress rupture properties of the alloy was investigated at 760 oC/758 MPa, 850 oC/550 MPa and 980 oC/250 MPa. SEM was used to study the fracture surface and the failure mechanism. The results show that when the misorientation angle of LAB is relatively small it has a less effect on the stress rupture properties of the alloy. The stress rupture properties decrease with the misorientation increase on the same test conditions. The fracture characteristic of specimen shows intergranular rupture trend with the misorientation increases on the same conditions or with increasing of temperature and decreasing of stress for the same misorientation of LAB
The slabs of the second generation single crystal superalloy DD6 were cast using bi-seeded crystals with symmetric twist low angle grain boundaries. The influence of low angle boundary (LAB) on the stress rupture properties of the alloy was investigated at 760 oC/758 MPa, 850 oC/550 MPa and 980 oC/250 MPa. SEM was used to study the fracture surface and the failure mechanism. The results show that when the misorientation angle of LAB is relatively small it has a less effect on the stress rupture properties of the alloy. The stress rupture properties decrease with the misorientation increase on the same test conditions. The fracture characteristic of specimen shows intergranular rupture trend with the misorientation increases on the same conditions or with increasing of temperature and decreasing of stress for the same misorientation of LAB
2012, 41(6):967-972.
Abstract:
The fatigue crack propagation behavior of as-extruded AZ31B magnesium alloy welded joint and heat affected zone have been studied. Compact tensions [C(T)] of welded joint [L-T(W)] and heat affected zone(welded joint is parallel [T-L(H)] and vertical [L-T(H)] to the extruded direction) were researched. Results indicate that the crack propagation direction is parallel to the extrusion direction for L-T(W); fatigue crack propagation rate is a rapid-slow process. T-L(H) is parallel to the notch direction and L-T(H) can be divided into two states (i.e., parallel to or angularly deflected towards the notch direction); crack propagation rate initially goes through a rapid course before it slows down. The fracture modes of crack tip remain a mixed-mode of transgranular and intergranular fractures. The fatigue fracture consists of quasi-cleavage and is a brittle fracture
The fatigue crack propagation behavior of as-extruded AZ31B magnesium alloy welded joint and heat affected zone have been studied. Compact tensions [C(T)] of welded joint [L-T(W)] and heat affected zone(welded joint is parallel [T-L(H)] and vertical [L-T(H)] to the extruded direction) were researched. Results indicate that the crack propagation direction is parallel to the extrusion direction for L-T(W); fatigue crack propagation rate is a rapid-slow process. T-L(H) is parallel to the notch direction and L-T(H) can be divided into two states (i.e., parallel to or angularly deflected towards the notch direction); crack propagation rate initially goes through a rapid course before it slows down. The fracture modes of crack tip remain a mixed-mode of transgranular and intergranular fractures. The fatigue fracture consists of quasi-cleavage and is a brittle fracture
2012, 41(6):973-977.
Abstract:
The effect of strain energy on Two-phase precipitation and Atoms occupying in Ni68.2Al22.7V9.1 alloy was studied, using the microscopic phase-field method. It is found that the strain energy significantly extend the precipitation process of L12 phase, and restrain the precipitation of DO22 phase. As DO22 phase decreases, the occupation probability of V atom at different sites in L12 phase increases, and the higher the strain energy, the greater the chance of occupying. The effect of strain energy on occupation probability of Al atom at α1 site in L12 phase is little, only a small reduction in amplitude, but it significantly reduces occupation probability of Al atom at α2 site and β site. In all cases, the occupation probability of V atom at β site in L12 phase is always higher than that at α site
The effect of strain energy on Two-phase precipitation and Atoms occupying in Ni68.2Al22.7V9.1 alloy was studied, using the microscopic phase-field method. It is found that the strain energy significantly extend the precipitation process of L12 phase, and restrain the precipitation of DO22 phase. As DO22 phase decreases, the occupation probability of V atom at different sites in L12 phase increases, and the higher the strain energy, the greater the chance of occupying. The effect of strain energy on occupation probability of Al atom at α1 site in L12 phase is little, only a small reduction in amplitude, but it significantly reduces occupation probability of Al atom at α2 site and β site. In all cases, the occupation probability of V atom at β site in L12 phase is always higher than that at α site
2012, 41(6):978-982.
Abstract:
This paper mainly aims at 7050 aluminum alloy to study the tensile mechanical performance of the plate with hole through testing and finite-element simulation. Then the cold working effects of different interferences (ranging from 0% to 11.11%) were compared and analyzed. Results show that compared with the standard specimens of 7050 aluminum alloy, for the plates with holes, their apparent strength, coefficient of elongation and modulus of elasticity are reduced, but the strains at plastic instability points are improved to a large extent. Cold working enhances the yield strength of the material around hole wall and improves the stress state of hole surface which make for peak stress weakened and enlarge the plane strain range along thickness direction of the hole. Meanwhile, the change of the tensile fracture with the cold working deformation degree present a regularity. Residual stress increases with interference increasing, and the position of peak stress transfers far from the wall of the hole along radial direction with interference increasing
This paper mainly aims at 7050 aluminum alloy to study the tensile mechanical performance of the plate with hole through testing and finite-element simulation. Then the cold working effects of different interferences (ranging from 0% to 11.11%) were compared and analyzed. Results show that compared with the standard specimens of 7050 aluminum alloy, for the plates with holes, their apparent strength, coefficient of elongation and modulus of elasticity are reduced, but the strains at plastic instability points are improved to a large extent. Cold working enhances the yield strength of the material around hole wall and improves the stress state of hole surface which make for peak stress weakened and enlarge the plane strain range along thickness direction of the hole. Meanwhile, the change of the tensile fracture with the cold working deformation degree present a regularity. Residual stress increases with interference increasing, and the position of peak stress transfers far from the wall of the hole along radial direction with interference increasing
2012, 41(6):983-988.
Abstract:
The precipitating behaviours of phases in alloy 690 affect intergranular corrosion resistance significantly. The effects of chemical composition and heat treatment temperature on equilibrium phases in alloy 690 were simulated with Thermo-Calc software. The content of C is found to affect precipitating behaviour of carbide intensively and those of α-Cr and γ′ phases slightly. The content of Cr affects the precipitating behaviour of these phases markedly. The content of Fe has little effect on the precipitating behaviour of equilibrium phases. Solution treatment temperature should be above 1050 ℃, and thermal treatment temperature should be above 700 ℃
The precipitating behaviours of phases in alloy 690 affect intergranular corrosion resistance significantly. The effects of chemical composition and heat treatment temperature on equilibrium phases in alloy 690 were simulated with Thermo-Calc software. The content of C is found to affect precipitating behaviour of carbide intensively and those of α-Cr and γ′ phases slightly. The content of Cr affects the precipitating behaviour of these phases markedly. The content of Fe has little effect on the precipitating behaviour of equilibrium phases. Solution treatment temperature should be above 1050 ℃, and thermal treatment temperature should be above 700 ℃
2012, 41(6):989-993.
Abstract:
By means of X-ray diffraction, γ′ phase and γ matrix lattice parameters and γ/γ′ misfit were measured in FGH97 PM superalloy with different hafnium contents. The results show that the lattice parameter of γ′ phase is smaller than that of γ matrix, and also the value of γ/γ′ misfit is negative. Hafnium mainly exists in γ' phase, the content of hafnium partitioning to γ' phase increases with increasing of hafnium contents in FGH97 PM superalloy, resulting in lattice parameter increasing and decreasing of the absolute value of γ/γ′ misfit.
By means of X-ray diffraction, γ′ phase and γ matrix lattice parameters and γ/γ′ misfit were measured in FGH97 PM superalloy with different hafnium contents. The results show that the lattice parameter of γ′ phase is smaller than that of γ matrix, and also the value of γ/γ′ misfit is negative. Hafnium mainly exists in γ' phase, the content of hafnium partitioning to γ' phase increases with increasing of hafnium contents in FGH97 PM superalloy, resulting in lattice parameter increasing and decreasing of the absolute value of γ/γ′ misfit.
2012, 41(6):994-997.
Abstract:
The element distribution in electrode surface, the microstructure and morphology of the W-15wt%Cu electric material were studied under DC condition. The transformation and erosion mechanism of the material in the DC arc was discussed. The results show that the DC arc causes the melting of the surface in anode, the transferring of copper ion and depositing on the cathode surface. The deposition of copper in cathode surface reduces the contact resistance. The decomposition of metal oxide is helpful to extinguish arc by absorbing the arc energy. Meanwhile the particles of W suspend in the melt pool which will increase the viscosity of the melt Cu and help to reduce the splash of melt drop and arc erosion. The W-15wt% Cu contact material shows better performance under DC condition compared to the other materials
The element distribution in electrode surface, the microstructure and morphology of the W-15wt%Cu electric material were studied under DC condition. The transformation and erosion mechanism of the material in the DC arc was discussed. The results show that the DC arc causes the melting of the surface in anode, the transferring of copper ion and depositing on the cathode surface. The deposition of copper in cathode surface reduces the contact resistance. The decomposition of metal oxide is helpful to extinguish arc by absorbing the arc energy. Meanwhile the particles of W suspend in the melt pool which will increase the viscosity of the melt Cu and help to reduce the splash of melt drop and arc erosion. The W-15wt% Cu contact material shows better performance under DC condition compared to the other materials
2012, 41(6):998-1003.
Abstract:
The orientation distribution of lamellar alpha in TC17 alloy was studied using quantitative metallography approach and finite element simulation. It is found that the orientation distribution of lamellar α varies with the value of strain. As the result, when the value of strain is below 0.38, the orientation distribution presents two symmetrical peaks, and the angle between the peaks is 90°, which indicates that lamellar α has a preferential orientation, and the microstructure shows a good agreement with initial lamellar microstructure. With the increase of strain, two asymmetric peaks appear in the orientation distribution of lamellar α, the volume fraction of lamellar α of one orientation peak increases and the angle between the peaks decreases. Initial basket structure is broken to different degree. When the value of the strain reaches about 0.7, the orientation approximately tends to present single-peak distribution with the preferential orientation of 80°~90°, lamellar α almost perpendicular to the direction of compression was observed
The orientation distribution of lamellar alpha in TC17 alloy was studied using quantitative metallography approach and finite element simulation. It is found that the orientation distribution of lamellar α varies with the value of strain. As the result, when the value of strain is below 0.38, the orientation distribution presents two symmetrical peaks, and the angle between the peaks is 90°, which indicates that lamellar α has a preferential orientation, and the microstructure shows a good agreement with initial lamellar microstructure. With the increase of strain, two asymmetric peaks appear in the orientation distribution of lamellar α, the volume fraction of lamellar α of one orientation peak increases and the angle between the peaks decreases. Initial basket structure is broken to different degree. When the value of the strain reaches about 0.7, the orientation approximately tends to present single-peak distribution with the preferential orientation of 80°~90°, lamellar α almost perpendicular to the direction of compression was observed
2012, 41(6):1004-1009.
Abstract:
The effects of aging treatments on the mechanical properties and corrosion behavior of 6156 A1 alloy were investigated by means of hardness measurement, conventional tensile test, slow strain rate tensile tests (SSRT) and intergranular corrosion test. The microstructures were observed with TEM. The results show that in T6 under-aging (T6UA) condition the precipitates are GP zones with high density in matrix, and no distinct grain boundary precipitates are observed. In T6 peak-aging (T6PA) condition the precipitates are β″ phase with high density and small amount of Q′ phase in matrix, the grain boundary precipitates are continuously distributed. The strength of T6 peak-aged 6156 alloy is the highest, however it has the serious tendency to intergranular corrosion and very high sensitivity to stress corrosion crack. With the aging time increasing, Q′ phase increases and coarsens, the grain boundary precipitates are coarsened obviously and sparsely distributed, precipitate free zone ( PFZ) appears. In T78 conditions, there are plenty of Q′ precipitates in matrix, and the coarse and isolate precipitates present in grain boundaries, and the PFZ is broaden. So the corrosion resistance is obviously improved while tensile strength is a little decreased.
The effects of aging treatments on the mechanical properties and corrosion behavior of 6156 A1 alloy were investigated by means of hardness measurement, conventional tensile test, slow strain rate tensile tests (SSRT) and intergranular corrosion test. The microstructures were observed with TEM. The results show that in T6 under-aging (T6UA) condition the precipitates are GP zones with high density in matrix, and no distinct grain boundary precipitates are observed. In T6 peak-aging (T6PA) condition the precipitates are β″ phase with high density and small amount of Q′ phase in matrix, the grain boundary precipitates are continuously distributed. The strength of T6 peak-aged 6156 alloy is the highest, however it has the serious tendency to intergranular corrosion and very high sensitivity to stress corrosion crack. With the aging time increasing, Q′ phase increases and coarsens, the grain boundary precipitates are coarsened obviously and sparsely distributed, precipitate free zone ( PFZ) appears. In T78 conditions, there are plenty of Q′ precipitates in matrix, and the coarse and isolate precipitates present in grain boundaries, and the PFZ is broaden. So the corrosion resistance is obviously improved while tensile strength is a little decreased.
2012, 41(6):1010-1015.
Abstract:
The β→α phase transition processes of Ti-5Al and Ti-10Al were studied by molecular dynamics simulation. The phase transitions of different Al contents were studied by the internal energy, radial distribution function and the contents of different structures. The evolution of the crystal structure during the phase transition was also observed and analyzed. The results show that the nucleation of Ti-10Al occurs faster than Ti-5Al, and Ti-10Al has a higher amount of precipitation of α phase; the phase transition process involves the shuffling of {110}β and is accompanied by a distortion; the crystallographic relationship between new phase and parent phase accords with {0001}α//{110}β; stacking faults and twin crystals are easily formed to reduce the stress caused by the phase transition
The β→α phase transition processes of Ti-5Al and Ti-10Al were studied by molecular dynamics simulation. The phase transitions of different Al contents were studied by the internal energy, radial distribution function and the contents of different structures. The evolution of the crystal structure during the phase transition was also observed and analyzed. The results show that the nucleation of Ti-10Al occurs faster than Ti-5Al, and Ti-10Al has a higher amount of precipitation of α phase; the phase transition process involves the shuffling of {110}β and is accompanied by a distortion; the crystallographic relationship between new phase and parent phase accords with {0001}α//{110}β; stacking faults and twin crystals are easily formed to reduce the stress caused by the phase transition
2012, 41(6):1016-1020.
Abstract:
By means of measurement of creep properties and microstructure observation, the creep behaviors of a single crystal nickel-based superalloy containing 4.2%Re were investigated. Results show that after fully heat treated, the microstructure of the alloy consists of the cubical γ￠ phase embedded in the γ matrix as coherent form. In the range of the applied stresses and test temperatures, compared to the free-Re superalloy, the superalloy with 4.2% Re possesses a better creep resistance and longer creep lifetime, and the creep activation energy and stress exponent of the alloy during steady state creep have been calculated. By means of analyzing the dislocation climbing over the rafted γ￠ phase and the factors effecting on strain rates of the alloy, the deformation mechanism of the alloy during steady state creep was investigated. Thereinto, dissolving of Re into the alloy matrix may hinder the dislocations movement and reduce the strain rate of the alloy, which is thought to be the main reason for the alloy possessing lower strain rate and longer creep lifetime.
By means of measurement of creep properties and microstructure observation, the creep behaviors of a single crystal nickel-based superalloy containing 4.2%Re were investigated. Results show that after fully heat treated, the microstructure of the alloy consists of the cubical γ￠ phase embedded in the γ matrix as coherent form. In the range of the applied stresses and test temperatures, compared to the free-Re superalloy, the superalloy with 4.2% Re possesses a better creep resistance and longer creep lifetime, and the creep activation energy and stress exponent of the alloy during steady state creep have been calculated. By means of analyzing the dislocation climbing over the rafted γ￠ phase and the factors effecting on strain rates of the alloy, the deformation mechanism of the alloy during steady state creep was investigated. Thereinto, dissolving of Re into the alloy matrix may hinder the dislocations movement and reduce the strain rate of the alloy, which is thought to be the main reason for the alloy possessing lower strain rate and longer creep lifetime.
2012, 41(6):1021-1025.
Abstract:
The Mo-Si alloy sheets with different silicon contents were fabricated by powder-metallurgical processing, and static tensile tests were performed at 25, 300, 800 and 1200 ℃, respectively. The effect of test temperatures on mechanical properties, facture mode and microstructure of Mo-Si alloys were studied. The results indicate that with increasing of tensile test temperature, the strength of the pure Mo and Mo-Si alloy sheets decrease dramatically, the elongation shows an increasing trend at lower 300 ℃ and then decreasing at higher temperatures. The fracture mode of molybdenum alloy sheets transform from transgranular cleavage fracture at room temperature to dimple fracture at 300 and 800 ℃, and then to intergranular fracture at 1200 ℃. The strengthening mechanism analysis results show that the strengthening of Mo-Si alloy originates from particle dispersion strengthening and solid solution strengthening at room temperature. While, at elevated temperature the role of solid solution strengthening weakens significantly and the particle dispersion strengthening and grain coarsening are main strengthening modes
The Mo-Si alloy sheets with different silicon contents were fabricated by powder-metallurgical processing, and static tensile tests were performed at 25, 300, 800 and 1200 ℃, respectively. The effect of test temperatures on mechanical properties, facture mode and microstructure of Mo-Si alloys were studied. The results indicate that with increasing of tensile test temperature, the strength of the pure Mo and Mo-Si alloy sheets decrease dramatically, the elongation shows an increasing trend at lower 300 ℃ and then decreasing at higher temperatures. The fracture mode of molybdenum alloy sheets transform from transgranular cleavage fracture at room temperature to dimple fracture at 300 and 800 ℃, and then to intergranular fracture at 1200 ℃. The strengthening mechanism analysis results show that the strengthening of Mo-Si alloy originates from particle dispersion strengthening and solid solution strengthening at room temperature. While, at elevated temperature the role of solid solution strengthening weakens significantly and the particle dispersion strengthening and grain coarsening are main strengthening modes
2012, 41(6):1026-1031.
Abstract:
The isothermal compression test of GH625 alloy was performed on Gleeble thermal simulator. A series of true stress-strain curves under different deformation conditions were obtained. The processing map of GH625 alloy in different strains was constructed according to DMM model, and the following conclusions can be obtained through the analysis of processing map. There exists an area in the processing map of GH625 alloy where the power dissipation efficiency is higher than that in others areas. The temperature corresponding the area is 1100~1200 ℃ and the strain rate is 0.01~1.0 s-1. In this area the alloy has completed fully dynamic recrystallization. When the power dissipation efficiency is in the range from 0.4 to 0.45, the dynamic recrystallization grains become finer. At the peak efficiency of 0.47, the dynamic recrystallization grains grow up apparently. There exists a small area of rheological instability in the processing map where the temperature is low, while the strain rate is high, and the dynamic recrystallization grains are distributed along the adiabatic shearing edges. The practical parameters of production processing should be chosen in fully dynamic recrystallization area, and the manufacturing in the instability zone should be avoided. According to the comprehensive mechanical properties of high temperature deformation, the microstructure evolution and the processing map of the GH625 alloy, we can get a suitable processing area, which is =0.01~1.0 s-1，T=1100~1200 ℃
The isothermal compression test of GH625 alloy was performed on Gleeble thermal simulator. A series of true stress-strain curves under different deformation conditions were obtained. The processing map of GH625 alloy in different strains was constructed according to DMM model, and the following conclusions can be obtained through the analysis of processing map. There exists an area in the processing map of GH625 alloy where the power dissipation efficiency is higher than that in others areas. The temperature corresponding the area is 1100~1200 ℃ and the strain rate is 0.01~1.0 s-1. In this area the alloy has completed fully dynamic recrystallization. When the power dissipation efficiency is in the range from 0.4 to 0.45, the dynamic recrystallization grains become finer. At the peak efficiency of 0.47, the dynamic recrystallization grains grow up apparently. There exists a small area of rheological instability in the processing map where the temperature is low, while the strain rate is high, and the dynamic recrystallization grains are distributed along the adiabatic shearing edges. The practical parameters of production processing should be chosen in fully dynamic recrystallization area, and the manufacturing in the instability zone should be avoided. According to the comprehensive mechanical properties of high temperature deformation, the microstructure evolution and the processing map of the GH625 alloy, we can get a suitable processing area, which is =0.01~1.0 s-1，T=1100~1200 ℃
2012, 41(6):1032-1037.
Abstract:
By the liquid metal cooling method, the microstructure character of directional solidification of Ti-45Al-7Nb (at%) alloy was examined. The results show that both the solidification behavior and lamellar orientations are affected by withdrawing rate. The primary phase is α phase, and lamellar orientation is perpendicular to the growth direction at the withdrawing rate of 0.36 mm/min. The primary phase converts into β phase at the withdrawing rate of 1~10 mm/min, alloy solidify completely into the β phase field, and lamellar orientation tends to parallel or incline with the angle of 45° to the growth direction. When the withdrawing rate increases to 20 mm/min, the primary is also β-phase, followed by the peritectic reaction of L + β → α, and lamellar orientation is inclined with the angle of 45°~75° to the withdrawing direction
By the liquid metal cooling method, the microstructure character of directional solidification of Ti-45Al-7Nb (at%) alloy was examined. The results show that both the solidification behavior and lamellar orientations are affected by withdrawing rate. The primary phase is α phase, and lamellar orientation is perpendicular to the growth direction at the withdrawing rate of 0.36 mm/min. The primary phase converts into β phase at the withdrawing rate of 1~10 mm/min, alloy solidify completely into the β phase field, and lamellar orientation tends to parallel or incline with the angle of 45° to the growth direction. When the withdrawing rate increases to 20 mm/min, the primary is also β-phase, followed by the peritectic reaction of L + β → α, and lamellar orientation is inclined with the angle of 45°~75° to the withdrawing direction
2012, 41(6):1038-1040.
Abstract:
The evolutions of microstructure and stress-rupture properties were investigated during aging at 700 and 900 ℃. With the increase of aging time at 700 ℃, the morphology, the size and the distribution of γ′ and carbides did not change, and the stress-rupture time was stable. During aging at 900 ℃, γ′ was coarsened to be worm-shaped. The worm-shaped microstructure was stable from 1007 h to 2014 h. The needle-like TCP phase was precipitated when the alloy was aged for 2014 h, but its content was very small. The stress-rupture time was only 30 h when the alloy was aged for 500 h. It was shortened by 50% in contrast to heat treated state. The stress-rupture time did not change from 1007 h to 2014 h
The evolutions of microstructure and stress-rupture properties were investigated during aging at 700 and 900 ℃. With the increase of aging time at 700 ℃, the morphology, the size and the distribution of γ′ and carbides did not change, and the stress-rupture time was stable. During aging at 900 ℃, γ′ was coarsened to be worm-shaped. The worm-shaped microstructure was stable from 1007 h to 2014 h. The needle-like TCP phase was precipitated when the alloy was aged for 2014 h, but its content was very small. The stress-rupture time was only 30 h when the alloy was aged for 500 h. It was shortened by 50% in contrast to heat treated state. The stress-rupture time did not change from 1007 h to 2014 h
2012, 41(6):1041-1044.
Abstract:
Based on the ability of nonlinear mapping and generalization, an artificial neural network model for the prediction of mechanical properties of hydrogenated TC21 titanium alloy was established. The input parameters of the neural network model includes temperature tensile testing temperature and hydrogen content. The outputs of the model are mechanical properties namely ultimate tensile strength and tensile yield strength. The accuracy of ANN model was tested by the test sample. It is found that the predicted results are in good agreement with experimental value because of the characters of good fault-tolerance and strong commonality. The trained model can predict the mechanical properties of hydrogenated TC21 alloy under the condition of different experimental temperatures and contents. With the help of application of neural network technology in the field of material preparation process and design, the efficiency can be improved greatly, and the cycle of the actual experiment will be shortened obviously.
Based on the ability of nonlinear mapping and generalization, an artificial neural network model for the prediction of mechanical properties of hydrogenated TC21 titanium alloy was established. The input parameters of the neural network model includes temperature tensile testing temperature and hydrogen content. The outputs of the model are mechanical properties namely ultimate tensile strength and tensile yield strength. The accuracy of ANN model was tested by the test sample. It is found that the predicted results are in good agreement with experimental value because of the characters of good fault-tolerance and strong commonality. The trained model can predict the mechanical properties of hydrogenated TC21 alloy under the condition of different experimental temperatures and contents. With the help of application of neural network technology in the field of material preparation process and design, the efficiency can be improved greatly, and the cycle of the actual experiment will be shortened obviously.
2012, 41(6):1045-1048.
Abstract:
In the present investigation a phase field model was used to analysis the processing of grain nucleation, and the nano-liked interface effect was introduced to describe the influence of the nucleation from grain growth kinetics. The precipitation of nuclei, the change of the nuclei number, the thickness of grain boundary and the feature of grain growth were studied at the same time. The simulation results show that the interface effect provides the driving power for nuclei growth, and the number of nuclei increases with prolonging of time, the radii of nuclei increase and the growth of nuclei changes fast. The distribution of the radius orientation reflects the change of grain boundary thickness and the grain size
In the present investigation a phase field model was used to analysis the processing of grain nucleation, and the nano-liked interface effect was introduced to describe the influence of the nucleation from grain growth kinetics. The precipitation of nuclei, the change of the nuclei number, the thickness of grain boundary and the feature of grain growth were studied at the same time. The simulation results show that the interface effect provides the driving power for nuclei growth, and the number of nuclei increases with prolonging of time, the radii of nuclei increase and the growth of nuclei changes fast. The distribution of the radius orientation reflects the change of grain boundary thickness and the grain size
2012, 41(6):1049-1052.
Abstract:
Different colors of oxide films were prepared directly on the TA2 pure titanium by constant voltage anodic oxidation in phosphate acid .The micro-morphologies, composition, components and valence bonds of the colored films were characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Energy disperse spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Tafel polarization curves and EIS of the colored films were studied by electrochemical workstation in Hank’s simulated body fluid. The SEM results show that the colored films of pure titanium after anodic oxidation are composed of porous surface and inner dense of oxide. The XRD study shows that the films are possessed of the amorphous structure of titanium dioxide. The XPS results indicate that the films are composed Ti4+ and O2-. With increasing of the voltage, the corrosion potential of colored films increases and corrosion current density decreases according to the Tafel polarization curves. The EIS exhibits that capacitive loop radius are enlarged and impedance values are increased with the increase of voltage, thus the corrosion performance of colored films is improved.
Different colors of oxide films were prepared directly on the TA2 pure titanium by constant voltage anodic oxidation in phosphate acid .The micro-morphologies, composition, components and valence bonds of the colored films were characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Energy disperse spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Tafel polarization curves and EIS of the colored films were studied by electrochemical workstation in Hank’s simulated body fluid. The SEM results show that the colored films of pure titanium after anodic oxidation are composed of porous surface and inner dense of oxide. The XRD study shows that the films are possessed of the amorphous structure of titanium dioxide. The XPS results indicate that the films are composed Ti4+ and O2-. With increasing of the voltage, the corrosion potential of colored films increases and corrosion current density decreases according to the Tafel polarization curves. The EIS exhibits that capacitive loop radius are enlarged and impedance values are increased with the increase of voltage, thus the corrosion performance of colored films is improved.
2012, 41(6):1055-1059.
Abstract:
Based on the sputtering theory and molecular thermodynamics theory, a mediated composition model of SmCo-based multinary alloy films was established, and the effect of sputtering parameters on the film composition was discussed. Subsequently, the SmCo-based multinary alloy films were deposited on Si substrates by magnetron sputtering from Sm(Co0.62Fe0.25Cu0.1Zr0.03)7.5 alloy target. The composition of the films prepared by different sputtering parameters was measured. The results show that the dependence of the film composition on sputtering parameters observed from the model agrees well with the experiment results, which gives a favorable support to the acquired model
Based on the sputtering theory and molecular thermodynamics theory, a mediated composition model of SmCo-based multinary alloy films was established, and the effect of sputtering parameters on the film composition was discussed. Subsequently, the SmCo-based multinary alloy films were deposited on Si substrates by magnetron sputtering from Sm(Co0.62Fe0.25Cu0.1Zr0.03)7.5 alloy target. The composition of the films prepared by different sputtering parameters was measured. The results show that the dependence of the film composition on sputtering parameters observed from the model agrees well with the experiment results, which gives a favorable support to the acquired model
2012, 41(6):1060-1064.
Abstract:
The sintered permanent magnets of (PrNd)33Al0.7Nb0.6Cu0.1B1.05Febal (wt%) were prepared by the high pressure and conventional molding processes. The performances and microstructure were discussed by metalloscope, VSM, SEM and so on. The results show that the Hcj and (BH)max of the samples by high pressure process (1.8 and 3.6 GPa) are much higher (133 kA·m-1 and 0.6 kJ·m-3; 120.3 kA·m-1 and 3.2 kJ·m-3) than those by the conventional pressure process. On the other hand, the former crystalline grains of NdFeB phase are thin and small. In addition, the former Nd-rich phases are homogeneous and reasonable, but too high pressure will decrease Vickers hardness of samples
The sintered permanent magnets of (PrNd)33Al0.7Nb0.6Cu0.1B1.05Febal (wt%) were prepared by the high pressure and conventional molding processes. The performances and microstructure were discussed by metalloscope, VSM, SEM and so on. The results show that the Hcj and (BH)max of the samples by high pressure process (1.8 and 3.6 GPa) are much higher (133 kA·m-1 and 0.6 kJ·m-3; 120.3 kA·m-1 and 3.2 kJ·m-3) than those by the conventional pressure process. On the other hand, the former crystalline grains of NdFeB phase are thin and small. In addition, the former Nd-rich phases are homogeneous and reasonable, but too high pressure will decrease Vickers hardness of samples
2012, 41(6):1065-1068.
Abstract:
The spark plasma sintering (SPS) technique was used to consolidate pre-alloyed powder of Ti-45Al-2Cr-2Nb-0.2W produced by plasma rotating electrode processing (PREP). The powder was sintered at temperatures between 1150 and 1250 oC，and the effects of sintering temperature on the microstructure and the mechanical properties were studied. The optimized conditions yield high densities and uniform microstructure. Specimens sintered at 1150 oC are characterized by fine duplex microstructure, leading to superior room temperature mechanical properties with a tensile strength of 1026 MPa and an elongation of 1.12%, while the specimen sintered at 1250 oC are of fully lamellar microstructure with a tensile strength of 953 MPa and an elongation of 0.92%. The main fracture mode in the duplex microstructure is transgranular in the equiaxed γ grains and interlamellar in the lamellar colonies, and for the fully lamellar microstructure the dominant fracture mode is interlamellar, translamellar and stepwise failure.
The spark plasma sintering (SPS) technique was used to consolidate pre-alloyed powder of Ti-45Al-2Cr-2Nb-0.2W produced by plasma rotating electrode processing (PREP). The powder was sintered at temperatures between 1150 and 1250 oC，and the effects of sintering temperature on the microstructure and the mechanical properties were studied. The optimized conditions yield high densities and uniform microstructure. Specimens sintered at 1150 oC are characterized by fine duplex microstructure, leading to superior room temperature mechanical properties with a tensile strength of 1026 MPa and an elongation of 1.12%, while the specimen sintered at 1250 oC are of fully lamellar microstructure with a tensile strength of 953 MPa and an elongation of 0.92%. The main fracture mode in the duplex microstructure is transgranular in the equiaxed γ grains and interlamellar in the lamellar colonies, and for the fully lamellar microstructure the dominant fracture mode is interlamellar, translamellar and stepwise failure.
2012, 41(6):1069-1074.
Abstract:
We used Zr66.7Ni33.3 binary alloys as base alloys and selected the intermetallic compound TiC as additional particles. The influence of TiC addition on the microstructural evolution induced by mechanical alloying has been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM)，transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The experimental results show that the proper addition of TiC (5wt%) not only shortens the starting time of the amorphization reaction, but also improves the glass forming ability (GFA) of Zr-Ni alloy powders and greatly enhances the mechanical stability of the amorphous composites. Based upon the EDX analysis, we have found that the diffusion of TiC among the atoms of Zr and Ni is inhomogeneous, leading to the increase of the disorder degree of atoms in local regions. Therefore, the TiC addition improves the GFA and stability of the Zr-Ni alloys. The DSC results demonstrate that the effect of the addition of 3 wt% TiC is better than that of the addition of 5 wt% TiC on the improvement of thermal stability of the amorphous phase, suggesting that there is no correlation between thermal stability and mechanical stability of MA induced Zr-Ni-based amorphous alloys
We used Zr66.7Ni33.3 binary alloys as base alloys and selected the intermetallic compound TiC as additional particles. The influence of TiC addition on the microstructural evolution induced by mechanical alloying has been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM)，transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The experimental results show that the proper addition of TiC (5wt%) not only shortens the starting time of the amorphization reaction, but also improves the glass forming ability (GFA) of Zr-Ni alloy powders and greatly enhances the mechanical stability of the amorphous composites. Based upon the EDX analysis, we have found that the diffusion of TiC among the atoms of Zr and Ni is inhomogeneous, leading to the increase of the disorder degree of atoms in local regions. Therefore, the TiC addition improves the GFA and stability of the Zr-Ni alloys. The DSC results demonstrate that the effect of the addition of 3 wt% TiC is better than that of the addition of 5 wt% TiC on the improvement of thermal stability of the amorphous phase, suggesting that there is no correlation between thermal stability and mechanical stability of MA induced Zr-Ni-based amorphous alloys
2012, 41(6):1075-1079.
Abstract:
Sulfuric acid solution was used to be the polishing slurry for the electropolishing of Ni5W alloy substrates prepared by rolling-assisted biaxially textured technology. The substrates with different surface states were obtained in several polishing slurry concentrations. The phase compositions of the surface mass and the microstructures were investigated by XPS, XRD, AFM and SEM, respectively. The results show that the low concentration polishing slurry promotes the excess production of oxides and H2WO4 which can disorder the process of selective solution disorder. The best effect can be obtained in 8.76 mol/L polishing slurry which promotes the formation of solid layer and mucus layer in proper thickness.
Sulfuric acid solution was used to be the polishing slurry for the electropolishing of Ni5W alloy substrates prepared by rolling-assisted biaxially textured technology. The substrates with different surface states were obtained in several polishing slurry concentrations. The phase compositions of the surface mass and the microstructures were investigated by XPS, XRD, AFM and SEM, respectively. The results show that the low concentration polishing slurry promotes the excess production of oxides and H2WO4 which can disorder the process of selective solution disorder. The best effect can be obtained in 8.76 mol/L polishing slurry which promotes the formation of solid layer and mucus layer in proper thickness.
2012, 41(6):1080-1084.
Abstract:
Mg-based hydrogen storage alloys Mg67-xCaxNi33 (x=0, 5, 10, 15, 20, at%) were prepared by means of induction melting，melt-spinning and ball milling. The effects of Ca content and preparation technologies on phase composition and hydrogen storage properties were studied. The results show that the preparation technologies (as-cast, casting + ball milling and casting + melt-spinning + ball milling) have little effect on the phase composition. The alloys containing Ca can form amorphous after melt-spinning. Mg67Ni33 alloy are mainly composed of Mg2Ni and a little quantity of Mg. The content of Mg2Ni decreases, while MgNi2 and Mg2Ca increase with the increase of Ca content in Mg67-xCaxNi33 alloys. When Ca content reaches 20at%, Mg47Ca20Ni33 alloy mainly consist of MgNi2 and Mg2Ca phase. P-C-T tests show that the maximum hydrogen storage capacity of Mg67-xCaxNi33 alloys decreases with increase of Ca content due to the decrease of Mg2Ni phase. After hydrogen absorption, Mg67Ni33 consists of Mg2NiH4 phase, while Ca containing alloys Mg67-xCaxNi33 alloys consist of Mg2NiH4, CaH2 and MgNi2
Mg-based hydrogen storage alloys Mg67-xCaxNi33 (x=0, 5, 10, 15, 20, at%) were prepared by means of induction melting，melt-spinning and ball milling. The effects of Ca content and preparation technologies on phase composition and hydrogen storage properties were studied. The results show that the preparation technologies (as-cast, casting + ball milling and casting + melt-spinning + ball milling) have little effect on the phase composition. The alloys containing Ca can form amorphous after melt-spinning. Mg67Ni33 alloy are mainly composed of Mg2Ni and a little quantity of Mg. The content of Mg2Ni decreases, while MgNi2 and Mg2Ca increase with the increase of Ca content in Mg67-xCaxNi33 alloys. When Ca content reaches 20at%, Mg47Ca20Ni33 alloy mainly consist of MgNi2 and Mg2Ca phase. P-C-T tests show that the maximum hydrogen storage capacity of Mg67-xCaxNi33 alloys decreases with increase of Ca content due to the decrease of Mg2Ni phase. After hydrogen absorption, Mg67Ni33 consists of Mg2NiH4 phase, while Ca containing alloys Mg67-xCaxNi33 alloys consist of Mg2NiH4, CaH2 and MgNi2
2012, 41(6):1085-1089.
Abstract:
The Nb-Mo-Si eutectic alloys were prepared using Optical Floating Zone (OFZ) directional solidification method. The effects of rod rotation speed and withdrawal rate on the eutectic morphology were examined. Results show that the rotation speed of seed rod has an obvious effect on structure morphology, while the rotation speed of starting sample rod has unobvious effect. When the withdrawal rate is 5 mm/h, and the seed rod doesn’t rotate, a regular Nbss-β(Nb,Mo)5Si3 lamellar structure can be obtained. When the seed rod rotates, some spherical particles and regular lamellar structure firstly appear in the center area of the sample, and then expand outwards along radius direction. Afterwards, the regular lamellar structure is gradually transferred into irregular and broken lamellar structure. When the withdrawal rate is between 3 and 5 mm/h, it is regular lamellar structure. At 10 mm/h, columnar and cellular structures co-exist. At 1 mm/h, the lamellar structure is degenerated and Nb-ss tends to form a net-work structure. The variety of microstructure was discussed in terms of liquid/solid interface characterization and undercooling
The Nb-Mo-Si eutectic alloys were prepared using Optical Floating Zone (OFZ) directional solidification method. The effects of rod rotation speed and withdrawal rate on the eutectic morphology were examined. Results show that the rotation speed of seed rod has an obvious effect on structure morphology, while the rotation speed of starting sample rod has unobvious effect. When the withdrawal rate is 5 mm/h, and the seed rod doesn’t rotate, a regular Nbss-β(Nb,Mo)5Si3 lamellar structure can be obtained. When the seed rod rotates, some spherical particles and regular lamellar structure firstly appear in the center area of the sample, and then expand outwards along radius direction. Afterwards, the regular lamellar structure is gradually transferred into irregular and broken lamellar structure. When the withdrawal rate is between 3 and 5 mm/h, it is regular lamellar structure. At 10 mm/h, columnar and cellular structures co-exist. At 1 mm/h, the lamellar structure is degenerated and Nb-ss tends to form a net-work structure. The variety of microstructure was discussed in terms of liquid/solid interface characterization and undercooling
2012, 41(6):1090-1093.
Abstract:
A series of Gd1- xNbx(x=0, 1, 2, 3, 5) alloys were prepared by arc melting in purified argon atmosphere. The ingots were heat-treated at 1273K for 96h followed by water quenching to homogenize the microstructure. All Gd1-xNbx alloys with various Nb doping keep the hexagonal crystal structure of pure Gd. The Curie temperatures Tc of the Nb-doped alloys are lower than that of Gd by ~2 K and the magnetic transition occurring in the vicinity of Tc is a second order transformation. The maximum entropy changes of Gd1-xNbx alloys under 5 T magnetic field are about 85% of that of pure Gd. The microhardness of Gd1- xNbx alloys is greatly improved by doping a small amount of Nb (≤5 at%). Comparing with pure Gd, the microhardness increases by about 53% for Gd1-xNbx alloys with x=5. The present results indicate that the Gd1- xNbx alloys with small amounts of Nb doping have large values of magnetic entropy change and good processing properties, they are possessed of great potential in room-temperature magnetic refrigeration applications
A series of Gd1- xNbx(x=0, 1, 2, 3, 5) alloys were prepared by arc melting in purified argon atmosphere. The ingots were heat-treated at 1273K for 96h followed by water quenching to homogenize the microstructure. All Gd1-xNbx alloys with various Nb doping keep the hexagonal crystal structure of pure Gd. The Curie temperatures Tc of the Nb-doped alloys are lower than that of Gd by ~2 K and the magnetic transition occurring in the vicinity of Tc is a second order transformation. The maximum entropy changes of Gd1-xNbx alloys under 5 T magnetic field are about 85% of that of pure Gd. The microhardness of Gd1- xNbx alloys is greatly improved by doping a small amount of Nb (≤5 at%). Comparing with pure Gd, the microhardness increases by about 53% for Gd1-xNbx alloys with x=5. The present results indicate that the Gd1- xNbx alloys with small amounts of Nb doping have large values of magnetic entropy change and good processing properties, they are possessed of great potential in room-temperature magnetic refrigeration applications
2012, 41(6):1094-1096.
Abstract:
The hot rolling process of a low-density Nb-based alloy was carried out at 1000, 1100 and 1200 ℃, respectively. The microstructures of the samples were characterized by the optical microscopy, SEM and field emission TEM, and the tensile strength and elongation of the alloy were also tested. The results show that the alloys hot-rolled at 1200 and 1100 ℃ have excellent room and high temperature properties, the room temperature strength reaches 600 MPa and the elongation more than 12%, the high temperature strength reaches 80 MPa and the high-temperature elongation above 30%. It is also found that the tensile strength decreases and the plasticity increases with the increase of the rolling temperature. But the alloy hot-rolled at 1000 ℃ has lower mechanical properties and the surface of the tensile fracture shows brittle rupture at the room temperature
The hot rolling process of a low-density Nb-based alloy was carried out at 1000, 1100 and 1200 ℃, respectively. The microstructures of the samples were characterized by the optical microscopy, SEM and field emission TEM, and the tensile strength and elongation of the alloy were also tested. The results show that the alloys hot-rolled at 1200 and 1100 ℃ have excellent room and high temperature properties, the room temperature strength reaches 600 MPa and the elongation more than 12%, the high temperature strength reaches 80 MPa and the high-temperature elongation above 30%. It is also found that the tensile strength decreases and the plasticity increases with the increase of the rolling temperature. But the alloy hot-rolled at 1000 ℃ has lower mechanical properties and the surface of the tensile fracture shows brittle rupture at the room temperature
2012, 41(6):1097-1100.
Abstract:
Bismuth and Tellurium nanoparticles were prepared by evaporation-condensation method in argon atmosphere, and n-type Bi2Te3 fine-grained thermoelectric bulk materials were fabricated by spark plasma sintering (SPS) at different temperatures from 663 to 723 K using mechanically alloyed (MA) powders. The phase compositions of powder and bulk samples were characterized by X-ray diffraction (XRD). The sizes and microscopic structures of nanoparticles and fractured cross section of the bulk samples were observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. The thermoelectric transport properties were measured at 323~473 K. The results show that electrical transport properties are almost unchanged but thermal conductivity is reduced significantly from 1.93 W/m·K to 1.29 W/m·K at 423 K for the fine-grained bulks prepared by nanoparticles comparing with coarse-grained materials. The maximum ZT value after SPS at 693 K reaches 0.68 at 423 K
Bismuth and Tellurium nanoparticles were prepared by evaporation-condensation method in argon atmosphere, and n-type Bi2Te3 fine-grained thermoelectric bulk materials were fabricated by spark plasma sintering (SPS) at different temperatures from 663 to 723 K using mechanically alloyed (MA) powders. The phase compositions of powder and bulk samples were characterized by X-ray diffraction (XRD). The sizes and microscopic structures of nanoparticles and fractured cross section of the bulk samples were observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. The thermoelectric transport properties were measured at 323~473 K. The results show that electrical transport properties are almost unchanged but thermal conductivity is reduced significantly from 1.93 W/m·K to 1.29 W/m·K at 423 K for the fine-grained bulks prepared by nanoparticles comparing with coarse-grained materials. The maximum ZT value after SPS at 693 K reaches 0.68 at 423 K
33 Study of Technology and Properties for Pulse Electrodeposition Nanocrystalline Fe-Ni-Cr Alloy Foil
2012, 41(6):1101-1106.
Abstract:
Fe-Ni-Cr alloy foil was pulse electrodeposited from the trivalent chromium bath. Orthogonal design was used to optimize the processing parameters. The effects of the electrodeposition parameters such as complexing agent and temperature on the composition of alloy foil were investigated systematically. The Fe-Ni-Cr alloy foil was characterized by SEM, EDS and XRD. The optimal process conditions are followed as that: 50 g·L-1 CrCl3·6H2O, with 16 A·dm-2 current density, the period with 100 ms, the duty cycle with 0.3, at 60 ℃ temperature in the solution of pH 1~1.5 with 45 minutes electroplating. The 20-30 μm thick Fe-Ni-Cr alloy foil with a smooth and uniform appearance was obtained, which contains (62~67)wt% Fe, (30~33)wt%Ni and (3~5)wt% Cr. The results indicate the alloy foil is piled up compactly with sphericity and its grain size less than 100 nm; and the main phases are the α-Fe or γ-Fe solid solution with Cr. When Cr content exceeds 4wt%, the main phase would be γ-Fe. The alloy foil also exhibits better electrical, mechanical performance and corrosion resistance with 68.66×10-6 Ω·cm resistivity, 5819 MPa micro-hardness and 1.685×10-6A·cm-2 corrosion current density in 3.5%NaCl solution respectively. Furthermore, the mechanism of co-deposition Fe-Ni-Cr was studied by means of polarization curve and cyclic voltammetry. The results demonstrate that the complexing agent changes the deposited potential of Fe, Ni, Cr, respectively and makes the co-deposition possible
Fe-Ni-Cr alloy foil was pulse electrodeposited from the trivalent chromium bath. Orthogonal design was used to optimize the processing parameters. The effects of the electrodeposition parameters such as complexing agent and temperature on the composition of alloy foil were investigated systematically. The Fe-Ni-Cr alloy foil was characterized by SEM, EDS and XRD. The optimal process conditions are followed as that: 50 g·L-1 CrCl3·6H2O, with 16 A·dm-2 current density, the period with 100 ms, the duty cycle with 0.3, at 60 ℃ temperature in the solution of pH 1~1.5 with 45 minutes electroplating. The 20-30 μm thick Fe-Ni-Cr alloy foil with a smooth and uniform appearance was obtained, which contains (62~67)wt% Fe, (30~33)wt%Ni and (3~5)wt% Cr. The results indicate the alloy foil is piled up compactly with sphericity and its grain size less than 100 nm; and the main phases are the α-Fe or γ-Fe solid solution with Cr. When Cr content exceeds 4wt%, the main phase would be γ-Fe. The alloy foil also exhibits better electrical, mechanical performance and corrosion resistance with 68.66×10-6 Ω·cm resistivity, 5819 MPa micro-hardness and 1.685×10-6A·cm-2 corrosion current density in 3.5%NaCl solution respectively. Furthermore, the mechanism of co-deposition Fe-Ni-Cr was studied by means of polarization curve and cyclic voltammetry. The results demonstrate that the complexing agent changes the deposited potential of Fe, Ni, Cr, respectively and makes the co-deposition possible
2012, 41(6):1107-1110.
Abstract:
Mo-Ti-Zr-TiC alloy was prepared via powder metallurgy method. The effects of trace TiC additive on the mechanical properties and microstructure of TiC reinforced Mo-Ti-Zr-TiC alloy were studied. The results indicate that the relative density and the tensile strength at room temperature of Mo-Ti-Zr-TiC alloy is effectively enhanced by adding trace TiC (0.1wt%~0.5wt%). The tensile strength achieves the highest value when the content of TiC is 0.4wt%, which is 28.1% higher than that of Mo-Ti-Zr alloy. The adding of trace TiC can inhibit the grain growth during alloy sintering process, which leads to the decrease of grain sizes with the rise of TiC content. A part of the fine TiC particles react with trace oxygen in molybdenum matrix to form (Mo,Ti)xOyCz compound second phase particles during high temperature sintering, while the other part are agglomerated into large particles, which play a role in grain boundaries purification and dispersion-strengthening.
Mo-Ti-Zr-TiC alloy was prepared via powder metallurgy method. The effects of trace TiC additive on the mechanical properties and microstructure of TiC reinforced Mo-Ti-Zr-TiC alloy were studied. The results indicate that the relative density and the tensile strength at room temperature of Mo-Ti-Zr-TiC alloy is effectively enhanced by adding trace TiC (0.1wt%~0.5wt%). The tensile strength achieves the highest value when the content of TiC is 0.4wt%, which is 28.1% higher than that of Mo-Ti-Zr alloy. The adding of trace TiC can inhibit the grain growth during alloy sintering process, which leads to the decrease of grain sizes with the rise of TiC content. A part of the fine TiC particles react with trace oxygen in molybdenum matrix to form (Mo,Ti)xOyCz compound second phase particles during high temperature sintering, while the other part are agglomerated into large particles, which play a role in grain boundaries purification and dispersion-strengthening.
2012, 41(6):1111-1115.
Abstract:
AZ31B magnesium alloy was joined by friction stir welding (FSW) and submerged friction stir welding (SFSW), respectively, and the microstructure and mechanical properties of the joints were investigated. The experimental results show that the nugget zone in SFSW joint is characterized by fine and equiaxed recrystallized grains. Increasing of the travel speed will induce an increase in grain size and a decrease in microhardness in the nugget zone. The microstructure of the FSW joint on the surface is coarser and more inhomogeneous than that in the center, while the microstructure of the SFSW joint on the surface is obviously finer than that in the center. The microhardness of the FSW joint on the surface is lower than that in the center, while the SFSW joint has the opposite trend. When the rotation speed is 950 r·min-1 and the travel speed is 75 mm·min-1, the maximum ultimate tensile strength of the SFSW joint reaches 72% that of the base material. The fracture surface of the SFSW joints exhibits cleavage-like feature
AZ31B magnesium alloy was joined by friction stir welding (FSW) and submerged friction stir welding (SFSW), respectively, and the microstructure and mechanical properties of the joints were investigated. The experimental results show that the nugget zone in SFSW joint is characterized by fine and equiaxed recrystallized grains. Increasing of the travel speed will induce an increase in grain size and a decrease in microhardness in the nugget zone. The microstructure of the FSW joint on the surface is coarser and more inhomogeneous than that in the center, while the microstructure of the SFSW joint on the surface is obviously finer than that in the center. The microhardness of the FSW joint on the surface is lower than that in the center, while the SFSW joint has the opposite trend. When the rotation speed is 950 r·min-1 and the travel speed is 75 mm·min-1, the maximum ultimate tensile strength of the SFSW joint reaches 72% that of the base material. The fracture surface of the SFSW joints exhibits cleavage-like feature
2012, 41(6):1116-1118.
Abstract:
A novel Nd-Fe-B based permanent magnets named as SPSed NdFeB magnets were prepared by spark plasma sintering (SPS) technique. In order to better comprehend the mechanism of the changes in magnetic properties of the SPSed NdFeB magnets treated in an optimized process, the effects of the heat treatment process on the microstructure of magnets were systematically studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS)，high-resolution transmission electron microscopy (HRTEM), respectively. The results show that the increase in coercivity of the magnet is related to the obvious decrease in ratio of Fe to RE (Fe/Re) in Re-rich phase，and the RE-rich phase transforms to crystalline state from amorphous state after heat treatment process.
A novel Nd-Fe-B based permanent magnets named as SPSed NdFeB magnets were prepared by spark plasma sintering (SPS) technique. In order to better comprehend the mechanism of the changes in magnetic properties of the SPSed NdFeB magnets treated in an optimized process, the effects of the heat treatment process on the microstructure of magnets were systematically studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS)，high-resolution transmission electron microscopy (HRTEM), respectively. The results show that the increase in coercivity of the magnet is related to the obvious decrease in ratio of Fe to RE (Fe/Re) in Re-rich phase，and the RE-rich phase transforms to crystalline state from amorphous state after heat treatment process.
2012, 41(6):1119-1123.
Abstract:
Accumulated annealing parameter has been widely used for indicating the corrosion resistance of Zircaloys. However, for Nb-containing zirconium alloys, a unanimous conclusion has not been drawn yet. Even more, some researchers confirm that the accumulated annealing parameter is totally inadequate in this type of alloy. Based on its physical nature, we summarize the correlation of the accumulated annealing parameter and alloy microstructure. Further, the reason why it can identify the corrosion resistance in some specific alloys is explained tentatively. It is suggested that the diffusion rate of alloying elements (Fe and Cr diffusing fast while Nb diffusing extraordinarily slow) determines whether the accumulated annealing parameter will work. A clear conclusion is drawn that the accumulated annealing parameter can identify the low-Nb zirconium alloy’s corrosion resistance, i.e., the smaller the value of the accumulated annealing parameter, the finer the second phase particles and then the better the corrosion resistance of alloy
Accumulated annealing parameter has been widely used for indicating the corrosion resistance of Zircaloys. However, for Nb-containing zirconium alloys, a unanimous conclusion has not been drawn yet. Even more, some researchers confirm that the accumulated annealing parameter is totally inadequate in this type of alloy. Based on its physical nature, we summarize the correlation of the accumulated annealing parameter and alloy microstructure. Further, the reason why it can identify the corrosion resistance in some specific alloys is explained tentatively. It is suggested that the diffusion rate of alloying elements (Fe and Cr diffusing fast while Nb diffusing extraordinarily slow) determines whether the accumulated annealing parameter will work. A clear conclusion is drawn that the accumulated annealing parameter can identify the low-Nb zirconium alloy’s corrosion resistance, i.e., the smaller the value of the accumulated annealing parameter, the finer the second phase particles and then the better the corrosion resistance of alloy
2012, 41(6):1124-1128.
Abstract:
氢渗透合金膜是一种重要的氢气提纯材料。本文简要介绍了目前存在的几种氢渗透合金膜的研究进展和各自的优缺点，重点讨论了氢渗透合金膜的工作原理、氢渗透性能和制备方法；详细分析了影响氢渗透性能的关键因素，包括氢渗透系数、氢扩散系数、氢溶解系数和氢脆性，提出了通过改善氢渗透合金膜的微观结构以提高膜材料的抗氢脆性、提高氢渗透系数和扩散系数的方法，最后对合金膜的发展趋势进行了探讨
氢渗透合金膜是一种重要的氢气提纯材料。本文简要介绍了目前存在的几种氢渗透合金膜的研究进展和各自的优缺点，重点讨论了氢渗透合金膜的工作原理、氢渗透性能和制备方法；详细分析了影响氢渗透性能的关键因素，包括氢渗透系数、氢扩散系数、氢溶解系数和氢脆性，提出了通过改善氢渗透合金膜的微观结构以提高膜材料的抗氢脆性、提高氢渗透系数和扩散系数的方法，最后对合金膜的发展趋势进行了探讨
