Molecular dynamics simulations of the effects of defects on martensite nucleation

The effects of various lattice defects, such as a single edge dislocation, dislocation configurations, a low-angle grain boundary, and a high-angle grain boundary, on martensite nucleation and growth were investigated by performing molecular dynamics simulations, using EAM interatomic potentials for Ni–Al alloy. Stress induced and thermally activated martensitic transformations were studied in the cases that various defects were introduced into the simulated system. The simulation results show that the nucleation patterns were closely related to the stresses of the dislocation configurations, in the sense that the locations where stresses assist the lattice distortion of the transformation are favorable for martensite nucleation. A symmetric, tilt low-angle grain boundary is not favorable for martensite nucleation, because the stresses of the constituent dislocations cancel one another and stresses that assist the lattice distortion cannot be produced. The low-angle boundary hinders the martensite growth due to the high stability of this type of dislocation configuration. A relaxed, high-angle grain boundary (coincident site lattice) is also not favorable for martensite nucleation, because of the lack of long-range stress field.