Co_(2)VZ(Z=Ga,Si)合金马氏体相变的第一性原理计算

First-principles study of martensite transformation and mechanical properties of Co_(2)VZ(Z=Ga,Si)alloys

计算不同磁有序下的相稳定性及弹性常数对实验上设计具有良好性能的Co2VZ(Z=Ga,Si)基形状记忆合金具有重要意义。采用精确Muffin-Tin轨道结合相干势近似方法,系统计算了0 K下Co2VZ基合金立方奥氏体和四方马氏体相的晶格结构、磁矩、弹性常数及总能。结果表明,在FM状态下,Co2VGa具有L21立方结构,当磁无序度y≥0.2时发生马氏体相变,具有D022四方结构;无论在FM还是PM状态下,Co_(2)VSi均能发生马氏体相变。Co_(2)VGa和Co_(2)VSi的总磁矩主要源于Co原子;它们对应L21相的总磁矩远大于D022相,导致由FM到PM的磁激发过程D022相电子总能相对越来越低。在2种状态下,Co2VSi的四方剪切弹性常数C′((C_(11)-C_(12))/2)值均较小,因而更容易发生马氏体相变。该结果有望为实验上Co2VZ基合金形状记忆及力学性能的优化提供理论参考。

Calculating the phase stability and elastic constant under different magnetic order is of great significance to the experimental design of Co_(2)VZ(Z=Ga,Si)-based shape memory alloys with good performance.Using the accurate Muffin-Tin orbit combined with the coherence potential approximation method,the lattice structure,magnetic moment,elastic constant and total energy of Co_(2)VZ-based alloy cubic austenite and tetragonal martensite phase at 0 K were calculated systematically.The results show that in the FM state,Co2VGa has an L2_(1) cubic structure.When the degree of magnetic disorder y≥0.2,a martensitic transformation occurs,and it has a D022 tetragonal structure;whether in FM or PM state,Co2VSi can generate martensite Phase change.The total magnetic moments of Co_(2)VGa and Co2VSi are mainly derived from Co atoms;their total magnetic moments corresponding to the L2_(1) phase are much larger than the D0_(22) phase,which leads to the relatively lower total electron energy of the D0_(22) phase during the magnetic excitation process from FM to PM.In both states,the tetragonal shear elastic constant C′((C_(11)-C_(12))/2)of Co2VSi is smaller,so it is more prone to martensitic transformation.This result is expected to provide a theoretical reference for the optimization of the shape memory and mechanical properties of Co_(2)VZ-based alloys in experiments.