High-rate Plastic Deformation of Nanocrystalline Tantalum to Large Strains: Molecular Dynamics Simulation

TL;DR

This study uses large-scale molecular dynamics simulations to explore high-rate plastic deformation in nanocrystalline tantalum, revealing dislocation and twinning mechanisms influencing strain hardening at large strains.

Contribution

It introduces a novel technique for analyzing local grain orientation and provides detailed insights into deformation mechanisms in nanocrystalline tantalum.

Findings

Dislocation and twinning are key deformation mechanisms.

Plastic deformation mechanisms depend on strain rate.

Weak strain hardening observed due to grain size and mechanisms.

Abstract

Here we use large-scale molecular dynamics (MD) simulations of the high-rate deformation of nanocrystalline tantalum to investigate the processes associated with plastic deformation for strains up to 100%. We use initial atomic configurations that were produced through simulations of solidification in the work of Streitz et al [Phys. Rev. Lett. 96, (2006) 225701]. These 3D polycrystalline systems have typical grain sizes of 10-20 nm. We also study a rapidly quenched liquid (amorphous solid) tantalum. We apply a constant volume (isochoric), constant temperature (isothermal) shear deformation over a range of strain rates, and compute the resulting stress-strain curves to large strains for both uniaxial and biaxial compression. We study the rate dependence and identify plastic deformation mechanisms. The identification of the mechanisms is facilitated through a novel technique that computes the local grain orientation, returning it as a quaternion for each atom. We find both dislocation and twinning processes are important, and they interact in the weak strain hardening in these extremely fine-grained microstructures.