The phase field method was applied to study the microstructure evolution of Ni4Ti3 precipitates during stress-free and stress-assisted aging of bi-crystalline NiTi shape memory alloys （SAMs） with two different initi...The phase field method was applied to study the microstructure evolution of Ni4Ti3 precipitates during stress-free and stress-assisted aging of bi-crystalline NiTi shape memory alloys （SAMs） with two different initial Ni-contents of 51.5% and 52.5% （mole fraction）, respectively. The simulation results show that, during stress-free aging of the NiTi alloy with a low supersaturation of Ni （i.e., Ti-51.5%Ni）, the Ni4Ti3 precipitates exhibit a heterogeneous distribution with a high number density of particles at the grain boundary, leaving most of the grain interiors free of precipitates; while for the NiTi alloy with a high supersaturation of Ni （i.e., Ti-52.5%Ni）, the Ni4Ti3 precipitates show a homogeneous distribution across the entire simulation system. The stress-assisted aging can give rise to homogeneous distribution of the precipitates, regardless of the initial Ni-content; however, the distribution of variant type within the two grains is heterogeneous.展开更多
The effect of deformation on recovery stress of Ni144.7Ti46.3Nb9 alloy has been studjed using tensile test at various temperatures and TEM observation. It ls shown that the recovery stress increases with jncreasing to...The effect of deformation on recovery stress of Ni144.7Ti46.3Nb9 alloy has been studjed using tensile test at various temperatures and TEM observation. It ls shown that the recovery stress increases with jncreasing total strain ET and reaches a maximum value (max) as ET= 9% but the maximum recov erV strain of the alloy is only about 4.6%. This is different from that of Ti-Ni binary alloy in which is obtained usually at maximum recovery strain and the reason of the difference is dis Cussed. Deformation temperature Td has a little effect on recovery stress when Td is less than Ms However, recovery stress decreases sharply when Td is higher than M, and lowers approximately down to zero near Msσ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 influence of aging treatment on transformation behavior and shape memory of the Ti 50_x Ni_(48) Fe_2 Nb_x(x=0,0.6,0.8,1.0,and 1.2) alloys was investigated using differential scanning calorimeter(DSC),mechanical dr...The influence of aging treatment on transformation behavior and shape memory of the Ti 50_x Ni_(48) Fe_2 Nb_x(x=0,0.6,0.8,1.0,and 1.2) alloys was investigated using differential scanning calorimeter(DSC),mechanical drawing machine,and microhardness tester in this paper.It is indicated that the aging treatment has a significant effect on the phase transformation temperatures(M_s,M_f,M_p,A_s,A_f,and A_p) and microhardness of the samples.The phase transformation temperatures are found to decrease initially with the increasing aging temperature from 300 to 500 ℃ and increase with further increase of the aging temperature.The aging treatment at intermediate temperature between 400 and 500 ℃ results in an improved shape memory effect.In addition,the highest microhardness value is also obtained.展开更多
The recovery strain, stress and transformation temperature of different pre-strained specimens of Ti44Ni47Nb9 were investigated by tensile test and electrical resistance measurement. The results indicated that pre-str...The recovery strain, stress and transformation temperature of different pre-strained specimens of Ti44Ni47Nb9 were investigated by tensile test and electrical resistance measurement. The results indicated that pre-strain increases the reverse martensitic transformation temperature (A ' (s)) and hysteresis (A(s) - M-s). The recovery strain and stress are higher if the specimens are pre-strained between M-s and A(s) temperature than outside this temperature range. There exists an optimal pre-strain value, about 10%, at which the specimen exhibits maximum recovery strain and stress.展开更多
Based on the alloy Cu55Ni45 (at pct), holding the proportion of Cu to Ni in constant and in the temperature range of 1233~1573 K, the wetting angles of CuNi-0~56 at pct Ti alloys on Si3N4 have been measured by the ses...Based on the alloy Cu55Ni45 (at pct), holding the proportion of Cu to Ni in constant and in the temperature range of 1233~1573 K, the wetting angles of CuNi-0~56 at pct Ti alloys on Si3N4 have been measured by the sessile drop method. With the increase of Ti content, the wetting angles decreased. The equilibrium wetting angle was 5° when Ti content ≥32 at pct.In the case of same Ti content, the activity of Ti in CuNiTi alloy was weaker than that in CuTi alloy The cross-section of the CuNiTi-Si3N4 interface and the elements distribution were examined by scanning electron microscope with X-ray wave-dispersion spectrometer, and the reaction products formed at the interface were determined by X-ray diffiaction analysis method.展开更多
A two-way shape memory effect (TWSM E) in the Ti46.3Ni44.7Nb9 alloy has been systematically investigated by means of bending test and transmission electron microscopy (TEM ) observations. Based on the analysis of the ...A two-way shape memory effect (TWSM E) in the Ti46.3Ni44.7Nb9 alloy has been systematically investigated by means of bending test and transmission electron microscopy (TEM ) observations. Based on the analysis of the microstructure after training. the mechanism of TWSME in the Ti46.3 Ni44.7Nb9 alloy has been discussed.展开更多
基金Project (50871039) supported by the National Natural Science Foundation of ChinaProject (2011ZB0007) supported by the Fundamental Research Funds for Central Universities of ChinaProject (201104090881) support by China Postdoctoral Science Foundation
文摘The phase field method was applied to study the microstructure evolution of Ni4Ti3 precipitates during stress-free and stress-assisted aging of bi-crystalline NiTi shape memory alloys （SAMs） with two different initial Ni-contents of 51.5% and 52.5% （mole fraction）, respectively. The simulation results show that, during stress-free aging of the NiTi alloy with a low supersaturation of Ni （i.e., Ti-51.5%Ni）, the Ni4Ti3 precipitates exhibit a heterogeneous distribution with a high number density of particles at the grain boundary, leaving most of the grain interiors free of precipitates; while for the NiTi alloy with a high supersaturation of Ni （i.e., Ti-52.5%Ni）, the Ni4Ti3 precipitates show a homogeneous distribution across the entire simulation system. The stress-assisted aging can give rise to homogeneous distribution of the precipitates, regardless of the initial Ni-content; however, the distribution of variant type within the two grains is heterogeneous.
文摘The effect of deformation on recovery stress of Ni144.7Ti46.3Nb9 alloy has been studjed using tensile test at various temperatures and TEM observation. It ls shown that the recovery stress increases with jncreasing total strain ET and reaches a maximum value (max) as ET= 9% but the maximum recov erV strain of the alloy is only about 4.6%. This is different from that of Ti-Ni binary alloy in which is obtained usually at maximum recovery strain and the reason of the difference is dis Cussed. Deformation temperature Td has a little effect on recovery stress when Td is less than Ms However, recovery stress decreases sharply when Td is higher than M, and lowers approximately down to zero near Msσ
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.
基金supported by the National Natural Science Foundation of China (No. 50921003)
文摘The influence of aging treatment on transformation behavior and shape memory of the Ti 50_x Ni_(48) Fe_2 Nb_x(x=0,0.6,0.8,1.0,and 1.2) alloys was investigated using differential scanning calorimeter(DSC),mechanical drawing machine,and microhardness tester in this paper.It is indicated that the aging treatment has a significant effect on the phase transformation temperatures(M_s,M_f,M_p,A_s,A_f,and A_p) and microhardness of the samples.The phase transformation temperatures are found to decrease initially with the increasing aging temperature from 300 to 500 ℃ and increase with further increase of the aging temperature.The aging treatment at intermediate temperature between 400 and 500 ℃ results in an improved shape memory effect.In addition,the highest microhardness value is also obtained.
文摘The recovery strain, stress and transformation temperature of different pre-strained specimens of Ti44Ni47Nb9 were investigated by tensile test and electrical resistance measurement. The results indicated that pre-strain increases the reverse martensitic transformation temperature (A ' (s)) and hysteresis (A(s) - M-s). The recovery strain and stress are higher if the specimens are pre-strained between M-s and A(s) temperature than outside this temperature range. There exists an optimal pre-strain value, about 10%, at which the specimen exhibits maximum recovery strain and stress.
文摘Based on the alloy Cu55Ni45 (at pct), holding the proportion of Cu to Ni in constant and in the temperature range of 1233~1573 K, the wetting angles of CuNi-0~56 at pct Ti alloys on Si3N4 have been measured by the sessile drop method. With the increase of Ti content, the wetting angles decreased. The equilibrium wetting angle was 5° when Ti content ≥32 at pct.In the case of same Ti content, the activity of Ti in CuNiTi alloy was weaker than that in CuTi alloy The cross-section of the CuNiTi-Si3N4 interface and the elements distribution were examined by scanning electron microscope with X-ray wave-dispersion spectrometer, and the reaction products formed at the interface were determined by X-ray diffiaction analysis method.
文摘A two-way shape memory effect (TWSM E) in the Ti46.3Ni44.7Nb9 alloy has been systematically investigated by means of bending test and transmission electron microscopy (TEM ) observations. Based on the analysis of the microstructure after training. the mechanism of TWSME in the Ti46.3 Ni44.7Nb9 alloy has been discussed.
