Molecular Dynamics Modeling of the Effect of Nanotwins on the Superelasticity of Single-Crystalline NiTi Alloys

Abstract

The objective of this work is to simulate the superelasticity and shape-memory effect in a single-crystalline nickel-titanium (NiTi) alloy through a molecular dynamics (MD) study. Cooling and heating processes for this material are reproduced to investigate the temperature-induced phase transformation in its microstructure. It is found that the martensitic transformation and its reverse process occur accompanied by an abrupt volume change, and the transformed variants lead to the appearance of the (001) type compound twin. In addition, the transform temperatures for martensite start ( ) and austenite finish ( ) are determined, respectively. The results indicate that when the temperature is beyond during the compressive loadingunloading, the superelastic behavior becomes pronounced, which is attributed to the role of nanotwins on the transformation from the austenitic phase (B2) to martensitic phase (B19 ). Compared to existing experimental data, a reasonable agreement is achieved through the modeling results, highlighting the importance of the compound twins for dominating the superelasticity of nanostructured NiTi alloys.

A Unified Empirical Equation for Determining the Mechanical Properties of Porous NiTi Alloy: From Nanoporosity to Microporosity

“…This potential reproduces the physical properties of NiTi for a wide thermodynamic region, as has been shown previously in the works [62][63][64]. In Equation (A1), E is the total energy of the system; F i (ρ i ) is the embedding function for the atom i within the background electron density ρ i ; the pair potential φ ij (r ij ) and the screening function S ij are evaluated at the distance r ij between atoms i and j; the cutoff radius of this potential is 5.0 Å for the considered binary system.…”