第一性原理研究压力下NiTi合金B2相的结构、力学以及热力学性质

运用第一性原理研究0~40 GPa下B2相NiTi合金的机械性能、 电子性质以及热力学性能. 计算发现, 几何优化后NiTi晶体的晶格常数与实验值和其他文献提供的数值大体一致, 表明随着压力的增加该型合金力学稳定且没有相变产生. NiTi合金的体模量B、 剪切模量G和杨氏模量E以及B/G的值随压力增大呈线性增加, 表明压力使其抗体积变形能力、 抗剪变能力及塑性增强. 研究发现, 压力也会使NiTi合金的各向异性发生改变. 对NiTi合金态密度的研究表明, 该合金同时显现出共价性与离子性, 并且压力对其电子性质无明显影响. 此外, 本文还研究了不同温度和压力下NiTi合金的热力学性能, 包括德拜温度ΘD,热容Cv和Cp的变化, 为今后实验提供理论数据.

Study on structural,mechanical and thermodynamic properties of B2 NiTi under pressures based on first-principles

We employ density functional theory to study the mechanical, electronic and thermodynamic properties of the cubic NiTi in a prssure range of 0-40 GPa.The calculated lattice parameters are well in agreement with experimental values and other calculated results, showing that the B2 NiTi is mechanically stable and no phase transformation occurs with pressure going up to 40 GPa.The bulk modulus B, shear modulus G, Young's modulus E and B/G of B2 NiTi improve linearly with increasing pressure, implying that the volume change resistance, shear deformation resistance and elastic stiffness could also be strengthened by pressure.The pressure could also have an influence on the ductility of NiTi.The density of state (DOS) of NiTi indicates that the bonding nature of B2 NiTi is metallic combining with covalent bonding, and pressure has no significant influence on the electronic properties in a pressure range of 0-40 GPa.In addition, the dependences of temperature and pressure on Debye temperature ΘD, heat capacity Cv and Cp are further studied to figure out the thermodynamic properties of B2 NiTi.All above are especially useful to further study the properties of NiTi.