NiTi合金势能面的第一性原理研究

First principles study of potential energy curves of NiTi alloy

采用模守恒赝势(Lin方案)和平面波超软赝势对两种NiTi异构体超晶胞势能面进行了理论研究,结果表明:由于在绝对零度下B19′相总能量低于B2相总能量,B19′相更为稳定.对于B2相,合金化元素Au和Fe在Ni原子位处于势能面平衡点而Ni(Ni位)及位于Ti原子位的Ti,Zr和Al并非处于平衡位置.在B19′相,Ni,Au,Fe,Ti,Zr,Al均处于势能面平衡点.NiTi合金的马氏体相变应该主要是来自Ni、Ti原子位于势能面非平衡位置所致.

The potential energy curves of B2 and B19＇ phase for NiTi alloys were investigated with the norm-conserving and planewave ultrasoft pseudopotential in the local density approximation. Our results reveals that the B19＇ phase is more stable than the B2 phase at absolute zero temperature due to lower potential energy of the former. In the B2 phase, the alloying atoms Au and Fe （at Ni site） occupy the equilibrium positions, whereas Ti, Zr and Al （ at Ti site ） and Ni atoms are displaced from their equilibrium positions. In the B19＇ phase, all the above atoms are exactly located at the equilibrium positions. The martensitic transformation may mostly be ascribed to the non-global minimum positions that the Ni and Ti atoms occupy.