Atomic-scale simulation of martensitic phase transformations in NiAl

Thermodynamic and kinetic properties of the martensitic phase transformations (MPT) in a model NiAl alloy are studied using the molecular dynamics method. The interatomic potential of Farkas et al. is used. It allows simulating a quite realistic behavior of the MPT for this alloy. We observe a typical hysteretic behavior during the reversible MPT. The temperature and composition regimes appear to be in good agreement with the ones experimentally observed for the Ni-Al alloy system. A new way of characterizing the local structure is proposed and applied for the analysis of the phase transformation. The definition of the local order parameter is based on the technique of the common neighbor analysis and combined with the method of space tessellation in Voronoy polyhedra. With this parameter the phase transformation can be followed in time on an atomistic scale showing how the nucleation process and the volume fraction of the new phase evolve with time. In order to find the location of the MPT in the temperature-composition-stress diagram, the influence of shear stresses is investigated. The effects of grain boundaries are simulated. (C) 2007 Elsevier B.V. All rights reserved.