Atomistic Simulations of Nickel-Titanium Shape-Memory Alloys

Abstract

Shape-memory Alloys (SMAs) exhibit tremendous mechanical properties owing to their reversible phase transformation between the austenitic and the martensitic phase. Out of these, equi-atomic nickel-titanium (NiTi) alloys are the most widely used SMAs for various applications since the transformation occurs close to room temperature. Advances in SMA engineering can be propelled by understanding the fundamental behavior of these materials. Atomistic scale computational techniques provide an efficient way of doing this. The accuracy of such techniques is based on the underlying model that is used in these simulations. With advancements in computational power, the scope for building more accurate material models and simulating bigger and more realistic systems have increased. This thesis is focused on understanding NiTi behavior at an atomistic scale using such accurate models. The work done as a part of this thesis is twofold. Firstly, previously existing interatomic potential models are used to perform molecular dynamics (MD) simulations to describe various phase transformation phenomena in NiTi SMAs including pseudo-elasticity and shape-memory effect, thereby comparing the performance of these existing models. Secondly, a new NiTi interatomic potential is developed, using a database generated by performing Density Functional Theory (DFT) calculations, the performance of which is better than existing models.