The effect of heterogeneities on dislocation nucleation barriers from cracktips in α-Fe

Abstract

In this work, we employ atomistic models to examine how heterogeneities at or near a cracktip influence the barriers to dislocation nucleation. We conceive of two simple scenarios designed to probe spatial and chemical effects. In the first example, we probe the effect of surface steps along the crackfront. In the second case, substitutional solutes are introduced on the emission slip plane at and in front of the crackfront. The impact of these heterogeneities is assessed by comparing the activation energy barriers for dislocation nucleation with a cracktip of the same orientation and loading without the heterogeneities present. The impact on the activation energies for emission is shown to be a function of the heterogeneity density and the volume of activation required at a given stress intensity.