Ni_(50)Ti_(49)Nb_(1)合金的马氏体相变行为与超弹性

Martensitic transformation behavior and superelasticity of Ni_(50)Ti_(49)Nb_(1)alloy

通过室温拔丝与晶化退火工艺制得了不同晶粒尺寸的Ni_(50)Ti_(49)Nb_(1)和Ni_(50)Ti_(50)合金丝材。利用差示扫描量热仪(DSC)、电阻测试仪(ER)、X射线衍射仪(XRD)与透射电子显微镜(TEM)表征了样品的热致马氏体相变行为与微观组织结构,利用万能拉伸试验机测试了纳米晶样品在不同温度下的超弹特性。结果表明,两类合金的热致相变均随晶粒尺寸减小而愈发受制,当晶粒尺寸为纳米晶时,B19′相被完全抑制;低温时,纳米晶Ni_(50)Ti_(49)Nb_(1)样品R相受制更强。拉伸测试结果表明,纳米晶Ni_(50)Ti_(49)Nb_(1)样品在218~398 K温域内展现超弹性,显著优于纳米晶Ni_(50)Ti_(50)合金;前者相变临界应力以及应力滞后与温度呈非线性相关,与后者显著不同。研究结果有助于理解微量Nb掺杂对NiTi基合金相变行为与超弹性的影响规律,并为新型超弹合金设计提供思路。

Ni_(50)Ti_(49)Nb_(1)and Ni_( 50) Ti _(50) alloy wires with different grain sizes were prepared by wire drawing at room temperature and annealing process.The differential scanning calorimetry(DSC),electrical resistivity(ER)measurement,X-ray diffraction(XRD)and transmission electron microscope(TEM)were used to characterize the martensitic transformation behavior during cooling and heating and the microstructure.Superelastic properties were examined at different temperatures using a universal tensile machine.Results show that the phase transition of both types of alloys were increasingly suppressed with the reduction of grain size.When the grain size is nanocrystalline,the B19′phase was completely suppressed.The suppression of R phase in nanocrystalline Ni_(50)Ti_(49)Nb_(1)was particularly severe at low temperature.As tensile test results,nanocrystalline Ni_(50)Ti_(49)Nb_(1)alloy exhibited tensile superelasticity over 218-398 K,being significantly superior to nanocrystalline Ni _(50 )Ti _(50).Moreover,the critical stresses and stress hysteresis of the former changed with temperature in a non-linear manner,in sharp contrast to that of the latter.The results of this study may shed light in the understanding of the role of Nb on the phase transformation behavior and superelasticity of NiTi based alloys,and in the development of new superelastic alloys.