Nucleation of twinning dislocation loops in fcc metals

TL;DR

This paper investigates the fundamental mechanisms of twinning dislocation loop nucleation in fcc metals using atomistic and continuum models, revealing new insights into energy barriers, shear stress, and nucleation mechanisms.

Contribution

It introduces an alternate-shear nucleation mechanism and compares it with the conventional layer-by-layer model, providing detailed energy and stress analyses.

Findings

The alternate-shear mechanism has a lower nucleation stress than the conventional model.

Critical loop size and Burgers vector vary with applied shear load.

Energy barriers for nucleation are quantified for different mechanisms.

Abstract

Deformation twinning, which occurs in fcc metals only under particular conditions of intrinsic material properties, microstructure, and loading conditions, occupies an indispensable place in their deformation mechanism maps. Nonetheless, dedicated studies have seldom been carried out to explore the fundamental properties of twinning dislocations mediating this process. Here we employ a combination of atomistic computations and continuum modeling to investigate the nucleation of twinning dislocation loops in metals with fcc crystal structure. Besides the conventional layer-by-layer model of twin nucleation, the newly proposed alternate-shear mechanism has been investigated, and the energy barrier and shear stress for twinning loop nucleation have been determined. We find the nucleation stress in the latter mechanism to be smaller than that in the former. The study also highlights the non-uniform variations of the critical loop size and fractional Burgers vector with the applied shear load.