Toward the Exploration of the NiTi Phase Diagram with a Classical Force Field

Classical force fields, used for atomistic modeling of metal materials, are typically constructed to match low-temperature properties obtained in experiments or from quantum-level calculations. However, force fields can systematically fail to reproduce further fundamental parameters, such as the melting point. In this work, we present a modified force field for modeling metallic compounds, which has been implemented in the MBN Explorer software package. It is employed to simulate different regions of the composition temperature size phase diagram of nickel titanium nanoalloys with particular focus on the evaluation of the melting point of NixTi1-x(x = 0.45-0.55) systems. A near-equiatomic NiTi alloy is of paramount interest for biomedical and nanotechnology applications due to its shape memory behavior, but experiments and theory are inconsistent regarding its structural ground-state properties. The presented force field is used to predict the ground-state structure of an equiatomic NiTi nanoalloy. We observe that this compound does not possess the shape memory capacity because it stabilizes in the austenite instead of the required martensite crystalline phase. All results of our atomistic approach utilizing molecular dynamics and Monte Carlo techniques are in agreement with respective,,ab initio calculations and the available experimental findings.