TiNi合金B2奧氏體中Ti位Ni誘導的晶格失穩

TiNi合金B2奧氏體中Ti位Ni誘導的晶格失穩The lattice instability induced by Ti-site Ni in B2 austenite in TiNi alloy

提出了點缺陷擾動策略，并利用此策略證實鈦位鎳實際上引起了B2奧氏體局域晶格失穩。失穩終態相的結構特征是從擾動位出發的一維方向上的<100>B2原子列收縮和<111>B2原子列膨脹。失穩終態相的能量低于B2相，最低能量比B2相低20meV/atom，出現在鈦位鎳濃度達到2%~4%時。與奧氏體情況相反，鈦位鎳無法令B19′馬氏體失穩。鈦位鎳顯著降低鈦鎳合金相變溫度的現象一定程度上是來源于此。

The shape memory effect exists in the 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 Ti-Ni 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, we proposed a point-defect-perturbation strategy by which we proved 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 20meV/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 didn’t 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.

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