616 Ni-Ti合金における応力誘起非晶質化および結晶変態の原子レベル解析(G01-2 計算力学(2)破壊力学・材料解析,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

抄録

The mechanism of stress-induced amorphization and martensite transformation is analyzed at an atomic level by using molecular dynamics (MD). Calculation model for MD is made of Ni-Ti (B2 structure) alloy which has edge cracking. The framework of modified embedded atom method (MEAM) potential and its approximated expression are attempted to be adopted in order to reproduce amorphous structure. The pentagonal bipyramid which is used as one of noncrystalline models is focused on, and short-range order of amorphous is distinguished by detecting indices of (1551) and (1541) for bond pairs defined in CNA. Martensite phase (B19' structure) is distinguished by the analysis of lattice constants of primitive crystal unit. As a result, it is found that amorphous structure has concentrated on nearby crack. The change of shear component in stress tensor shows very similar trend for change of amorphization ratio defined here. On the other hand, the results show that tensile stress plays an important role in martensite transformation.