Molecular Dynamics Simulations on the Deformation Behavior of Shape Memory Alloy using Multi-Grain Models
Takuya UEHARA Chihiro ASAI and Nobutada OHNO
Abstract:Deformation mechanism of a shape memory alloy is investigated by molecular dynamics simulations using several multi-grain models. An EAM potential for Ni-Al alloy is applied, and a set of conditions with loading, unloading, heating and cooling is imposed. As a result, the stress-strain relation obtained by a multi-grain model revealed to draw a loop consisting of smooth curves which resembles experimentally obtained one, while previously-simulated single-crystal model produced a zigzag diagram. From the observation of the configuration of atoms and local structure during the deformation, it revealed that local deformation of martensite variants is initiated at grain boundaries, and also that the propagation of the deformed region is obstructed by the boundaries. The influence of the grain shape and distribution, as well as the crystal orientation of each grain, on the deformation behavior is then discussed: Qualitatively common features in deformation mechanism and stress-strain relation are observed despite different grain distributions, while quantitative values such as critical stresses are dependent on the crystal orientations of each grain and of the neighbors. Key Words:Molecular dynamics, Shape memory alloy, Phase transformation, Martensite, Deformation behavior, Numerical analysis