An empirical map of martensitic transformation temperatures versus average valence electrons per atom(ev/a) and valence electron concentration(cv) was developed in order to design Zr Cu-based shape memory alloys(SMAs)...An empirical map of martensitic transformation temperatures versus average valence electrons per atom(ev/a) and valence electron concentration(cv) was developed in order to design Zr Cu-based shape memory alloys(SMAs). The martensitic transformation temperatures of about 40 different alloys(Ni, Co, Hf, Ag, Ti, Al, Cr, etc.), covering nearly all possible replacements of Zr or Cu, are exhibited. The relationship between transformation temperature and cv or electron density(n) was determined. The results indicate that the transformation temperatures of Zr Cu-based alloys gradually decrease until reaching an inflection point at cv = 0.218, above which the transformation temperatures go down. A linear dependence of the transformation temperatures of Zr Cu-based alloys on the electron density is revealed by data-fitting. Under the guidance of these contour maps describing transformation temperatures and thermal hysteresis, a series of Zr Cu-based alloys that can function under different conditions can be designed.展开更多
In this paper a first-principles study of the electronic structure and stability of B2 Ti1-xNiHfx (x = 0.2, 0.4, 0.6) and B19′ Ti1-xNiHfx(x = 0, 0.5) alloys is presented. The calculations are performed by the pla...In this paper a first-principles study of the electronic structure and stability of B2 Ti1-xNiHfx (x = 0.2, 0.4, 0.6) and B19′ Ti1-xNiHfx(x = 0, 0.5) alloys is presented. The calculations are performed by the plane-wave pseudopotential method in the framework of the density functional theory with the generalized gradient approximation. This paper calculates the lattice parameters, density of states, charge density, and heats of formation. The results show that the electronic structure and stability of B2 Ti1-xNiHfx change gradually with Hf content. However, Hf content has little effect on the electronic structure and stability of B19′ Ti1-xNiHfx. The mechanism of the effect of Hf content on martensitic transformation temperature of TiNiHf alloys is studied from the electronic structure.展开更多
In this research, fabrication of a (Ti,Hf)-rich NiTiHf alloy by using vacuum induction melting (VIM) process and a graphitic crucible was investigated. For this purpose, casts with the nominal composition of Ni49T...In this research, fabrication of a (Ti,Hf)-rich NiTiHf alloy by using vacuum induction melting (VIM) process and a graphitic crucible was investigated. For this purpose, casts with the nominal composition of Ni49Ti38Hf15 were prepared in graphitic crucible and mold. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) tests were employed to characterize the samples. Results demonstrated that microstructure of the first cast was composted of a B2 austenite phase as well as a great amount of two differently formed (Ti,Hf)C carbides. Moreover, no austenite *-* martensite transformation peak was detected in the DSC curve of this sample, indicating a drastic decline in the transformation temperatures. In the succeeding cast, however, owing to the formation of carbide layers on the inner surfaces of the graphitic crucible and mold during the initial casting process, the amounts of carbides decreased remarkably. This cast exhibited transformation temperatures above 100℃, while XRD pattern denoted the presence of B19t monoclinic martensite phase at room temperature. All in all, results confirmed that VIM process using graphitic mold and crucible can be considered as an appropriate method for the fabrication of (Ti,Hf)-rich NiTiHf high temperature shape memory alloys.展开更多
Effect of γ-irradiation on the shape memory alloy CuZnAl has been studied by the techniques of TEM,positron annihilation etc..The martensitic transformation temperature of the alloy increases obviously ofter γ-irrad...Effect of γ-irradiation on the shape memory alloy CuZnAl has been studied by the techniques of TEM,positron annihilation etc..The martensitic transformation temperature of the alloy increases obviously ofter γ-irradiation at a dose of 2×10~7 Gy but not for a dose of 1× 10~7 Gy.The shape memory effect in both irradiated alloys remains unaffected.展开更多
The effects of heat treatment on the Cu-Zn-Al shape memory alloys with mixed REwere researched with the help of X-ray diffraction and transmission electron micro-scope (TEM).The results show that the shape memory allo...The effects of heat treatment on the Cu-Zn-Al shape memory alloys with mixed REwere researched with the help of X-ray diffraction and transmission electron micro-scope (TEM).The results show that the shape memory alloys with martensite can beproduced by adding mixed RE and heat treatment processes holding at 820C -880Cfor 15min,quenching into oil,aging at 150C for 15min,and then holding in waterat 50C for 10min.The alloys have the lowest transformation thermal hysteresis.Among the four experimental heat treatment processes the gradationally quenchingmakes the alloy have the highest transformation temperature and quenching into oilor water at room temperature makes the alloy have the largest thermal hysteresis.Mi-crostructure examination shows that aging at 2000C could destroy the substructuresin lathy martensites in the alloy and form a lot of dislocations,and aging at 250℃could cause the bainite transformation in the alloy.展开更多
基金supported by the National Natural Science Foundation of China(51171052 and 51322102)the Key Projects of Chinese National Programs for Fundamental Research and Development(2011CB012904 and 2012CB619400)+1 种基金the Doctoral Program Foundation of Institutions of Higher Education of China(20112302130006)the Fundamental Research Funds for the Central Universities(HIT.BRET III 201201)
文摘An empirical map of martensitic transformation temperatures versus average valence electrons per atom(ev/a) and valence electron concentration(cv) was developed in order to design Zr Cu-based shape memory alloys(SMAs). The martensitic transformation temperatures of about 40 different alloys(Ni, Co, Hf, Ag, Ti, Al, Cr, etc.), covering nearly all possible replacements of Zr or Cu, are exhibited. The relationship between transformation temperature and cv or electron density(n) was determined. The results indicate that the transformation temperatures of Zr Cu-based alloys gradually decrease until reaching an inflection point at cv = 0.218, above which the transformation temperatures go down. A linear dependence of the transformation temperatures of Zr Cu-based alloys on the electron density is revealed by data-fitting. Under the guidance of these contour maps describing transformation temperatures and thermal hysteresis, a series of Zr Cu-based alloys that can function under different conditions can be designed.
基金Project supported by the National Natural Science Foundation of China (Grant No 50471018).
文摘In this paper a first-principles study of the electronic structure and stability of B2 Ti1-xNiHfx (x = 0.2, 0.4, 0.6) and B19′ Ti1-xNiHfx(x = 0, 0.5) alloys is presented. The calculations are performed by the plane-wave pseudopotential method in the framework of the density functional theory with the generalized gradient approximation. This paper calculates the lattice parameters, density of states, charge density, and heats of formation. The results show that the electronic structure and stability of B2 Ti1-xNiHfx change gradually with Hf content. However, Hf content has little effect on the electronic structure and stability of B19′ Ti1-xNiHfx. The mechanism of the effect of Hf content on martensitic transformation temperature of TiNiHf alloys is studied from the electronic structure.
文摘In this research, fabrication of a (Ti,Hf)-rich NiTiHf alloy by using vacuum induction melting (VIM) process and a graphitic crucible was investigated. For this purpose, casts with the nominal composition of Ni49Ti38Hf15 were prepared in graphitic crucible and mold. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) tests were employed to characterize the samples. Results demonstrated that microstructure of the first cast was composted of a B2 austenite phase as well as a great amount of two differently formed (Ti,Hf)C carbides. Moreover, no austenite *-* martensite transformation peak was detected in the DSC curve of this sample, indicating a drastic decline in the transformation temperatures. In the succeeding cast, however, owing to the formation of carbide layers on the inner surfaces of the graphitic crucible and mold during the initial casting process, the amounts of carbides decreased remarkably. This cast exhibited transformation temperatures above 100℃, while XRD pattern denoted the presence of B19t monoclinic martensite phase at room temperature. All in all, results confirmed that VIM process using graphitic mold and crucible can be considered as an appropriate method for the fabrication of (Ti,Hf)-rich NiTiHf high temperature shape memory alloys.
文摘Effect of γ-irradiation on the shape memory alloy CuZnAl has been studied by the techniques of TEM,positron annihilation etc..The martensitic transformation temperature of the alloy increases obviously ofter γ-irradiation at a dose of 2×10~7 Gy but not for a dose of 1× 10~7 Gy.The shape memory effect in both irradiated alloys remains unaffected.
文摘The effects of heat treatment on the Cu-Zn-Al shape memory alloys with mixed REwere researched with the help of X-ray diffraction and transmission electron micro-scope (TEM).The results show that the shape memory alloys with martensite can beproduced by adding mixed RE and heat treatment processes holding at 820C -880Cfor 15min,quenching into oil,aging at 150C for 15min,and then holding in waterat 50C for 10min.The alloys have the lowest transformation thermal hysteresis.Among the four experimental heat treatment processes the gradationally quenchingmakes the alloy have the highest transformation temperature and quenching into oilor water at room temperature makes the alloy have the largest thermal hysteresis.Mi-crostructure examination shows that aging at 2000C could destroy the substructuresin lathy martensites in the alloy and form a lot of dislocations,and aging at 250℃could cause the bainite transformation in the alloy.