Atomistic simulations of ductile failure in a b.c.c. high entropy alloy

TL;DR

This study uses molecular dynamics simulations to investigate ductile failure mechanisms in a bcc high entropy alloy, revealing how void size influences elastic and plastic properties, and comparing its behavior to pure tantalum.

Contribution

It provides new insights into the failure mechanisms of bcc high entropy alloys, including dislocation nucleation, twinning, and the effects of element size mismatch, which were not previously characterized in detail.

Findings

Elastic modulus scales with porosity similarly to foams.

Dislocation nucleation stress depends on void radius and is lower than in pure Ta.

Twinning occurs as a deformation mechanism, with some detwinning at large strains.

Abstract

Ductile failure is studied in a bcc HfNbTaZr High Entropy Alloy (HEA) with a pre-existing void. Using molecular dynamics simulations of uniaxial tensile tests, we explore the effect of void radius on the elastic modulus and yield stress. The elastic modulus scales with porosity as in closed-cell foams. The critical stress for dislocation nucleation as a function of the void radius is very well described by a model designed after pure bcc metals, taking into account a larger core radius for the HEA. Twinning takes place as a complementary deformation mechanism, and some detwinning occurs at large strain. No solid-solid phase transitions are identified. The concurrent effects of element size mismatch and plasticity lead to significant lattice disorder. By comparing our HEA results to pure tantalum simulations, we show that the critical stress for dislocation nucleation and the resulting dislocation densities are much lower than for pure Ta, as expected from lower energy barriers due to chemical complexity