TiNi合金B2奥氏体中Ti位Ni诱导的晶格失稳

The Lattice Instability Induced by Ti-Site Ni in B2 Austenite in TiNi Alloy

提出了点缺陷扰动策略,并利用此策略证实Ti位Ni实际上引起了B2奥氏体局域晶格失稳。失稳终态相的结构特征是从扰动位出发的一维方向上的<100>B2原子列收缩和<111>B2原子列膨胀。失稳终态相的能量低于B2相,最低能量比B2相低20 meV/atom,在Ti位Ni浓度达到2%～4%时出现。与奥氏体情况相反,Ti位Ni无法令B19′马氏体失稳。Ti位Ni显著降低TiNi合金相变温度的现象一定程度上来源于此。

The shape memory effect exists in the temperature range between martensitic phase transformation temperature and reverse martensitic phase transformation temperature, thus the control of martensitic phase transformation temperature is a key issue for the application of shape memory alloys.Valence electrons have been thought to dominate phase stability and phase transformation temperature in TiNi alloy. Inconsistent with the valence electron theory, Ti-site Ni could lead to a significant decrease of phase transformation temperature in TiNi alloy. To deeply understand the effect of Ti-site Ni, a pointdefect-perturbation strategy was proposed to prove that Ti-site Ni indeed induced a local lattice instability in B2 austenite. It is the structural feature of instability final phase that one-dimensional <100>B2 atomic column compression and <111>B2 column expansion from the perturbation site. The final phase is energetic lower than B2 structure, and the lowest energy of final phase is 20 meV/atom lower than B2 structure,when the perturbing Ti-site Ni content reaches 2%~4%. In contrast to the case in austenite, Ti-site Ni did not induce the lattice instability in B19′ martensite. The difference between austenite and martensite is to some extent the origin of the significant decrease of phase transformation temperature brought by Ti-site Ni in TiNi alloy.