退火温度对铸态Ti_(49)Ni_(51)形状记忆合金微观组织和力学性能的影响

采用光学显微镜、X射线衍射仪(XRD)和万能试验机等仪器对铸态以及退火条件下Ti_(49)Ni_(51)形状记忆合金的微观组织和力学性能进行了研究。结果表明,合金随着退火温度的升高,晶粒逐渐由纤维状向等轴状过渡,晶粒变得粗大。XRD分析发现,对于铸态合金,在非晶态弥散衍射峰基础上呈现出Ti Ni晶体相衍射峰;样品在723 K和773 K退火,非晶态弥散衍射峰消失,XRD谱图上显示出现Ti Ni晶体相的衍射峰。Ti_(49)Ni_(51)合金在723 K和773 K温度下热处理30 min后进行压缩试验的结果表明,723 K热处理试样在加载过程中母相奥氏体朝马氏体起始转变应力σAs大于773 K热处理试样的母相奥氏体朝马氏体起始转变应力;然而,前者母相奥氏体朝马氏体完成转变应力σAf小于后者母相奥氏体朝马氏体完成转变应力;另外,在卸载试验中,前者的残余应变小于后者的残余应变。

Effect of microstructure and mechanical properties on annealing temperature in as-cast Ti49Ni51 shape memory alloy

In this paper, the microstructure and mechanical properties of Ti49Ni51 shape memory alloy were investigated by means of optical microscope, X-ray diffraction (XRD) and universal testing machine. The results show that the grain sizes of the alloy increases with the increase of the annealing temperature; in addition, the grain size is gradually changed from the like-fiber crystal to equal axis crystal. The diffraction peaks of TiNi crystal phase for the cast alloy were found on the basis of the non crystalline diffuse diffraction peak by the analysis of XRD; and the samples were annealed at 723K and 773K, the non crystalline diffuse diffraction peaks disappeared, a TiNi crystal phase is exhibited in the XRD curves. The Ti49Ni51 alloys with heat treatment of 723K and 773k at 30 min were compressed. The results show that, the beginging stress (sAs) of the austenite phase transformation the specimen at heat treatment of 723K is larger than that specimen at heat treatment of 773k; however, the finishing stress of austenite phase transformation for the former is smaller than for the latter; in addition, in unloading experiments, the residual strain of the former is less than that of the latter.