Molecular-dynamics study of martensitic transformations in sintered FeNi nanoparticles

Abstract

Nanocrystalline metals with grain sizes in the nanometer range often have interesting properties which differ from usual polycrystalline samples or single crystals. Here we report on the first molecular-dynamics simulations of martensitic transformations—i.e. structural transformations from fcc to bcc—in sintered FeNi nanoparticles. The atomic interactions were described by an embedded-atom method (EAM) potential specially designed to model the FeNi system. Simulations were carried out by applying a constant pressure and temperature ensemble (NPT ensemble) to 32 nanoparticles each containing slightly more than 1000 atoms. The nano-particles initially were placed with random crystallographic orientation on an fcc lattice such that the particles attract each other. After relaxation for 0.58 ns at a temperature of 800 K and a pressure of 0 GPa a polycrystalline sample with a density just about two percent larger than that of a perfect single crystal was achieved. Subsequent cooling towards low temperatures allows the study of the temperature-induced martensitic transformation at pre-existing defects.