The microstructure, martensite transformation behavior, thermal stability and shape memory behavior of Ti–20Zr– 10Ta high temperature shape memory alloy were investigated. The Ti–20Zr–10Ta alloy exhibited a revers...The microstructure, martensite transformation behavior, thermal stability and shape memory behavior of Ti–20Zr– 10Ta high temperature shape memory alloy were investigated. The Ti–20Zr–10Ta alloy exhibited a reversible transformation with the high martensite transformation temperature of 500oC and good thermal stability. The alloy displayed the elongation of 15% and a maximum recovery stain of 5.5% with 8% pre-strain.展开更多
The use of Ni-rich TiNiHf alloys as high temperature shape memory alloys （SMAs） through aging has been presented. For Ni-rich Ti80-xNixHf20 alloys, their phase transformation temperatures are averagely increased mor...The use of Ni-rich TiNiHf alloys as high temperature shape memory alloys （SMAs） through aging has been presented. For Ni-rich Ti80-xNixHf20 alloys, their phase transformation temperatures are averagely increased more than 100 K by aging at 823 K for 2 h. Especially for the alloys with Ni-content of 50.4 at. pct and 50.6 at. pct, their martensitic transformation start temperatures （Ms） are more than 473 K after aging. TEM observation confirmed that some fine particles precipitate from the matrix during aging. The aged Ni-rich TiNiHf SMAs show the better thermal stability of phase transformation temperatures than the solutiontreated TiNiHf alloys. The fine particles precipitated during aging should be responsible for the increase of phase transformation temperatures and its high stability.展开更多
Precipitate hardening is the most easiest and effective way to enhance strain recovery properties in NiTiHf high-temperature shape memory alloys.This paper discusses the precipitation,coarsening and age hardening of H...Precipitate hardening is the most easiest and effective way to enhance strain recovery properties in NiTiHf high-temperature shape memory alloys.This paper discusses the precipitation,coarsening and age hardening of H-phase precipitates in Ni_(50)Ti_(30)Hf_(20)alloy during isothermal aging at temperatures between 450℃and 650℃for time to 75 h.The H-phase mean size and volume fraction were determined using transmission electron microscopy.Precipitation kinetics was analyzed using the Johnson-Mehl-Avrami-Kolmogorov equation and an Arrhenius type law.From these analyses,a Time-Temperature-Transformation diagram was constructed.The evolution of H-phase size suggests classical matrix diffusion limited Lifshitz-Slyozov-Wagner coarsening for all considered temperatures.The coarsening rate constants of H-phase precipitation have been determined using a modified coarsening rate equation for nondilute solutions.Critical size of H-phase precipitates for breaking down the precipitate/matrix interface coherency was estimated through a combination of age hardening and precipitate size evolution data.Moreover,time-temperature-hardness diagram was constructed from the precipitation and coarsening kinetics and age hardening of H-phase precipitates in Ni_(50)Ti_(30)Hf_(20)alloy.展开更多
The effect of thermal cycling and aging in martensitic state in Ti-Pd-Ni alloys were investigated by DSC and TEM observations. It is shown that the thermal cycling causes the decreases in M, and Af temperatures in Ti5...The effect of thermal cycling and aging in martensitic state in Ti-Pd-Ni alloys were investigated by DSC and TEM observations. It is shown that the thermal cycling causes the decreases in M, and Af temperatures in Ti50Pd50-xNix (x=10, 20, 30) alloys, but no obvious thermal cycling effect was observed in Ti50Pd50Pd40Ni10 alloys and the aging effect shows a curious feature, i.e., the Af temperature does not saturate even after relatively long time aging, which is considered to be due to the occurrence of recovery recrystallization during aging.展开更多
The Effect of the thermal cycling training under constant strain on the two-way shape memory effect (TWSME) in a Ti36l\li49Hf15 high temperature shape memory alloy (SMA) has been investigated by bending tests. The res...The Effect of the thermal cycling training under constant strain on the two-way shape memory effect (TWSME) in a Ti36l\li49Hf15 high temperature shape memory alloy (SMA) has been investigated by bending tests. The results indicated that the training procedure is beneficial to get the better TWSME. The two-way shape memory strain increases with increasing the training strain. And it decreases with increasing the training temperature. The TWSME obtained in the present alloy shows poorer stability compared with that obtained in the TiNi alloys.展开更多
The effects of prestrain and annealing temperature on phase transformation temperatures in Fel4Mn5Si8Cr4Ni shape memory alloy have been studied. The results showed that when the annealing temperature was 673 K, both t...The effects of prestrain and annealing temperature on phase transformation temperatures in Fel4Mn5Si8Cr4Ni shape memory alloy have been studied. The results showed that when the annealing temperature was 673 K, both the At and the Ms temperatures increased appreciably as the prestrain increased, the As temperature increased slightly with increasing prestrain; the resistivity difference at 303 K between the heating and cooling curve also increased with increasing prestrain, which agreed with the recovery strain. The shape memory effect in Fe-Mn-Si-Cr-Ni shape memory alloy is caused by the stress-induced γ→ε martensite transformation and its reverse transformation. When the prestrain was 10%, the Ms temperature decreased remarkably as the annealing temperature increased.展开更多
In the present work,the effects of Ni doping on the microstructure and mechanical properties of Co-V-Ga high-temperature shape memory alloy have been studied.It has been found thatγphase occurs in the form of precipi...In the present work,the effects of Ni doping on the microstructure and mechanical properties of Co-V-Ga high-temperature shape memory alloy have been studied.It has been found thatγphase occurs in the form of precipitation or even dendrite microstructure when Ni content continuously increases in the alloy.The composition distribution showed the elements Co and Ni segregated in theγphase,while elements V and Ga concentrated in the martensite phase.Moreover,the phase transition temperature increased by Ni-doping in Co-V-Ga alloys due to the increase in e/a of the alloy.However,the abundant presence ofγphase hindered the shear phase transformation and created a large number of grain boundaries to reduce Ms temperature when Ni content continuously increased.In addition,electron backscattered diffraction(EBSD)results verified that the presence ofγphase could hinder the expansion of cracks,and improve the strength and plasticity of the alloy.Furthermore,it could be found the shape memory effect could maintain a relatively high recovery rate when Ni content was within a certain extent.However,the shape memory effect of the alloy significantly decreased in the presence ofγphase with dendrite microstructure.The current research results not only clarify the influence of Ni doping on the microstructure and mechanical behavior of Co-V-Ga alloys,but also provide guidance for element doping to prepare high-temperature shape memory alloys(HTSMAs)with excellent performance.展开更多
The work-hardening behaviour in an Fe-Mn-Si-Cr-Ni alloy has been investigated using tensile test at different temperatures and TEM observation. It was found that besides the intersection of εmartensite, the intersect...The work-hardening behaviour in an Fe-Mn-Si-Cr-Ni alloy has been investigated using tensile test at different temperatures and TEM observation. It was found that besides the intersection of εmartensite, the intersections of ε martensite with stacking fault and the cross-slip of dislocation which is difficult to occur in the alloy with low stacking fault energy are also important factors to the temperature dependent work-hardening behaviour.展开更多
The phase transformation behavior, mechanical properties, and the thermal stability of CuAlAg alloy were studied and minor rare earth (0.1 wt pct La+Ce) was added to improve the mechanical property of the studied allo...The phase transformation behavior, mechanical properties, and the thermal stability of CuAlAg alloy were studied and minor rare earth (0.1 wt pct La+Ce) was added to improve the mechanical property of the studied alloy. It was found that Ag addition in the CuAl binary alloy can improve the stability of martensitic transformation and high Al content leads to the disappearing of martensitic transformation. The tensile strength and strain of the Cu-10.6AI-5.8Ag (wt pct) alloy were measured to be 383.5 MPa and 0.86%, respectively. With rare earth addition, the tensile strain increased from 0.86% to 1.47%. The CuAlAg alloy did not exhibit martensitic transformation on the second heating process. Its poor thermal stability still needs to be improved.展开更多
In the present work,the microstructure features,martensitic transformation,mechanical properties and strain recovery characteristics of Ti-Ta based shape memory alloys were tailored by changing Hf contents.The single...In the present work,the microstructure features,martensitic transformation,mechanical properties and strain recovery characteristics of Ti-Ta based shape memory alloys were tailored by changing Hf contents.The singleα"martensite phase was dominated in Ti-Ta alloy with 2 at.%H f.Upon Hf content exceeded2 at.%,βphase started to appear.Moreover,the amount ofβphase gradually increased with Hf content increasing.The martensitic transformation temperatures continuously decreased with the increased Hf content,which was attributed to the rising of valence electron concentration.Meanwhile,Hf addition improved the thermal cycling stability of Ti-Ta alloys due to the suppression ofωprecipitation.The yield stress of Ti-Ta based alloys firstly decreased and then increased with Hf content increasing.In addition,the completely recoverable strain of 4%can be obtained in Ti-Ta alloy with 6 at.%Hf as a consequence of the higher critical stress for dislocation slip.Besieds,the Ti-Ta based alloy containing 8 at.%Hf had the superior superelasticity behavior with the fully recoverable strain of 2%at room temperature.展开更多
In order to further understand the characteristics of the floating potential of low earth orbit spacecraft,the effects of the electron current collection area,background electron temperature,photocurrent emission,spac...In order to further understand the characteristics of the floating potential of low earth orbit spacecraft,the effects of the electron current collection area,background electron temperature,photocurrent emission,spacecraft wake,and the shape of spacecraft on spacecraft floating potential were studied here by particle-in-cell simulation in the low earth orbit.The simulation results show that the electron current collection area and background electron temperature impact on the floating potential by changing the electron current collection of spacecraft.By increasing the electron current collection area or background electron temperature,the spacecraft will float at a lower electric potential with respect to the surrounding plasma.However,the spacecraft wake affects the floating potential by increasing the ion current collected by spacecraft.The emission of the photocurrent from the spacecraft surface,which compensates for the electrons collected from background plasma,causes the floating potential to increase.The shape of the spacecraft is also an important factor influencing the floating potential.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
基金Project supported by the National Natural Science Foundation of China （Grant Nos. 51071059 and 51271065） and the National Basic Research Program of China （Grant Nt）. 2012CB619400）
文摘The microstructure, martensite transformation behavior, thermal stability and shape memory behavior of Ti–20Zr– 10Ta high temperature shape memory alloy were investigated. The Ti–20Zr–10Ta alloy exhibited a reversible transformation with the high martensite transformation temperature of 500oC and good thermal stability. The alloy displayed the elongation of 15% and a maximum recovery stain of 5.5% with 8% pre-strain.
文摘The use of Ni-rich TiNiHf alloys as high temperature shape memory alloys （SMAs） through aging has been presented. For Ni-rich Ti80-xNixHf20 alloys, their phase transformation temperatures are averagely increased more than 100 K by aging at 823 K for 2 h. Especially for the alloys with Ni-content of 50.4 at. pct and 50.6 at. pct, their martensitic transformation start temperatures （Ms） are more than 473 K after aging. TEM observation confirmed that some fine particles precipitate from the matrix during aging. The aged Ni-rich TiNiHf SMAs show the better thermal stability of phase transformation temperatures than the solutiontreated TiNiHf alloys. The fine particles precipitated during aging should be responsible for the increase of phase transformation temperatures and its high stability.
基金supported by the National Natural Sci-ence Foundation of China(Nos.52050410340 and 51971072)the Fundamental Research Funds for the Central University(No.3072021CFJ1002).
文摘Precipitate hardening is the most easiest and effective way to enhance strain recovery properties in NiTiHf high-temperature shape memory alloys.This paper discusses the precipitation,coarsening and age hardening of H-phase precipitates in Ni_(50)Ti_(30)Hf_(20)alloy during isothermal aging at temperatures between 450℃and 650℃for time to 75 h.The H-phase mean size and volume fraction were determined using transmission electron microscopy.Precipitation kinetics was analyzed using the Johnson-Mehl-Avrami-Kolmogorov equation and an Arrhenius type law.From these analyses,a Time-Temperature-Transformation diagram was constructed.The evolution of H-phase size suggests classical matrix diffusion limited Lifshitz-Slyozov-Wagner coarsening for all considered temperatures.The coarsening rate constants of H-phase precipitation have been determined using a modified coarsening rate equation for nondilute solutions.Critical size of H-phase precipitates for breaking down the precipitate/matrix interface coherency was estimated through a combination of age hardening and precipitate size evolution data.Moreover,time-temperature-hardness diagram was constructed from the precipitation and coarsening kinetics and age hardening of H-phase precipitates in Ni_(50)Ti_(30)Hf_(20)alloy.
基金This work was supported by a Grant-in-Aid fOrEncouragement of Young Scientists (W.C.) (l998-1999) from the Ministry of Educat
文摘The effect of thermal cycling and aging in martensitic state in Ti-Pd-Ni alloys were investigated by DSC and TEM observations. It is shown that the thermal cycling causes the decreases in M, and Af temperatures in Ti50Pd50-xNix (x=10, 20, 30) alloys, but no obvious thermal cycling effect was observed in Ti50Pd50Pd40Ni10 alloys and the aging effect shows a curious feature, i.e., the Af temperature does not saturate even after relatively long time aging, which is considered to be due to the occurrence of recovery recrystallization during aging.
文摘The Effect of the thermal cycling training under constant strain on the two-way shape memory effect (TWSME) in a Ti36l\li49Hf15 high temperature shape memory alloy (SMA) has been investigated by bending tests. The results indicated that the training procedure is beneficial to get the better TWSME. The two-way shape memory strain increases with increasing the training strain. And it decreases with increasing the training temperature. The TWSME obtained in the present alloy shows poorer stability compared with that obtained in the TiNi alloys.
文摘The effects of prestrain and annealing temperature on phase transformation temperatures in Fel4Mn5Si8Cr4Ni shape memory alloy have been studied. The results showed that when the annealing temperature was 673 K, both the At and the Ms temperatures increased appreciably as the prestrain increased, the As temperature increased slightly with increasing prestrain; the resistivity difference at 303 K between the heating and cooling curve also increased with increasing prestrain, which agreed with the recovery strain. The shape memory effect in Fe-Mn-Si-Cr-Ni shape memory alloy is caused by the stress-induced γ→ε martensite transformation and its reverse transformation. When the prestrain was 10%, the Ms temperature decreased remarkably as the annealing temperature increased.
基金supported by the National Key R&D Program of China(Nos.2023YFB3506701 and 2022YFB3706801)the National Natural Science Foundation of China(Nos.52174365,52004155,and 52130204).
文摘In the present work,the effects of Ni doping on the microstructure and mechanical properties of Co-V-Ga high-temperature shape memory alloy have been studied.It has been found thatγphase occurs in the form of precipitation or even dendrite microstructure when Ni content continuously increases in the alloy.The composition distribution showed the elements Co and Ni segregated in theγphase,while elements V and Ga concentrated in the martensite phase.Moreover,the phase transition temperature increased by Ni-doping in Co-V-Ga alloys due to the increase in e/a of the alloy.However,the abundant presence ofγphase hindered the shear phase transformation and created a large number of grain boundaries to reduce Ms temperature when Ni content continuously increased.In addition,electron backscattered diffraction(EBSD)results verified that the presence ofγphase could hinder the expansion of cracks,and improve the strength and plasticity of the alloy.Furthermore,it could be found the shape memory effect could maintain a relatively high recovery rate when Ni content was within a certain extent.However,the shape memory effect of the alloy significantly decreased in the presence ofγphase with dendrite microstructure.The current research results not only clarify the influence of Ni doping on the microstructure and mechanical behavior of Co-V-Ga alloys,but also provide guidance for element doping to prepare high-temperature shape memory alloys(HTSMAs)with excellent performance.
文摘The work-hardening behaviour in an Fe-Mn-Si-Cr-Ni alloy has been investigated using tensile test at different temperatures and TEM observation. It was found that besides the intersection of εmartensite, the intersections of ε martensite with stacking fault and the cross-slip of dislocation which is difficult to occur in the alloy with low stacking fault energy are also important factors to the temperature dependent work-hardening behaviour.
基金supported by Aviation Science Foundation of China(ASFC),No.00G51007.
文摘The phase transformation behavior, mechanical properties, and the thermal stability of CuAlAg alloy were studied and minor rare earth (0.1 wt pct La+Ce) was added to improve the mechanical property of the studied alloy. It was found that Ag addition in the CuAl binary alloy can improve the stability of martensitic transformation and high Al content leads to the disappearing of martensitic transformation. The tensile strength and strain of the Cu-10.6AI-5.8Ag (wt pct) alloy were measured to be 383.5 MPa and 0.86%, respectively. With rare earth addition, the tensile strain increased from 0.86% to 1.47%. The CuAlAg alloy did not exhibit martensitic transformation on the second heating process. Its poor thermal stability still needs to be improved.
基金financially supported by the National Natural Science Foundation of China(Nos.51871080,51931004 and 51571073)the Talent Training Program for Shandong Province Higher Educational Youth Innovative Teams(2019)。
文摘In the present work,the microstructure features,martensitic transformation,mechanical properties and strain recovery characteristics of Ti-Ta based shape memory alloys were tailored by changing Hf contents.The singleα"martensite phase was dominated in Ti-Ta alloy with 2 at.%H f.Upon Hf content exceeded2 at.%,βphase started to appear.Moreover,the amount ofβphase gradually increased with Hf content increasing.The martensitic transformation temperatures continuously decreased with the increased Hf content,which was attributed to the rising of valence electron concentration.Meanwhile,Hf addition improved the thermal cycling stability of Ti-Ta alloys due to the suppression ofωprecipitation.The yield stress of Ti-Ta based alloys firstly decreased and then increased with Hf content increasing.In addition,the completely recoverable strain of 4%can be obtained in Ti-Ta alloy with 6 at.%Hf as a consequence of the higher critical stress for dislocation slip.Besieds,the Ti-Ta based alloy containing 8 at.%Hf had the superior superelasticity behavior with the fully recoverable strain of 2%at room temperature.
基金supported by National Natural Science Foundation of China(No.11105063)
文摘In order to further understand the characteristics of the floating potential of low earth orbit spacecraft,the effects of the electron current collection area,background electron temperature,photocurrent emission,spacecraft wake,and the shape of spacecraft on spacecraft floating potential were studied here by particle-in-cell simulation in the low earth orbit.The simulation results show that the electron current collection area and background electron temperature impact on the floating potential by changing the electron current collection of spacecraft.By increasing the electron current collection area or background electron temperature,the spacecraft will float at a lower electric potential with respect to the surrounding plasma.However,the spacecraft wake affects the floating potential by increasing the ion current collected by spacecraft.The emission of the photocurrent from the spacecraft surface,which compensates for the electrons collected from background plasma,causes the floating potential to increase.The shape of the spacecraft is also an important factor influencing the floating potential.
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.
