Ni—Ti合金的R相变及其对形状记忆效应的影响

Occurrence of R Phase Transition and Its Influence on Shape Memory Effect in Ni-Ti Alloy

采用电阻测量和X-射线衍射研究了Ti-54.91wt%Ni合金发生R相变的固溶和有序化处理条件。比较了不同残余应变量下经过 R 相变和只经过熟知的马氏体相变两种试样间的形状记忆特性。在近似等原子的 Ni-Ti 合金中 R 相变的发生取决于热处理条件。除非在最有利的固溶和有序化组合条件下,通常并不存在 R 相变。延长有序化时间总是促进 R 相变。随着马氏体应变量的增大,不论是否附加 R 相变,形状回复温区加宽,单程形状回复率增高并出现极大值,而双程记忆效应单调地升高。在该合金中 R 相变的发生对于单程回复是有益的,但对于双程记忆则稍有削弱。形成 R相的热处理条件可以用声子形核的概念来解释。R 相变在单程和双程记忆上的不同效果可归因于加热(仅 M→B_2)和冷却(B_2→R 和 R→M)中经历不同的相变。

The condition of heat treatment including solution treatment and ordering for the formation of R phase transition in a 54.91 wt% Ni-Ti alloy is studied by means of electrical resistance measurement and X-ray diffraction.Comparison of shape memory characteristics under various amounts of the residual strain is made between specimen undergoing a R phase transition and that associated only with the well-known martensitic transformation.In near equiatomic Ni-Ti alloy,the occurrence of R phase transition depends on the condition of heat treatment,and usually there does not exist R phase transition unless under an optimum combination of solutionization and ordering.Prolonged ordering always promotes R phase transition.The temperature interval of the shape recovery widens,the one-way shape recovery ratio increases to a maximum value and the two-way memory effect increases monotonically with the increment of the strain of mar tensite,no matter whether the alloy has been superimposed with a R phase transition or not.The occurrence of R phase transition in the alloy under study is beneficial to one-way recovery.The condition of heat treatment for the formation of the R phase may be interpreted by the application of the phonon nucleation concept.The different effect of R phase transition on the one-way and two-way shape memory may be attributed to the different transformation upon heating(only M→B_2)and cooling(B_2→R and R→M).