Plasticity induced anelasticity: The atomistic origin

Abstract

Plastic deformation is associated with developments in both dislocation density and residual strain. This study used multi-scale diffraction-based, X-ray as well as electron diffraction, measurements to quantify and relate them. Though both increased with progressive tensile deformation, an inverse orientation dependent relationship clearly emerged. In particular, higher elastically strained regions were accommodated by dislocation walls of lower residual strain. These experimental observations provided a combined perspective of elastic-plastic strain gradients in experimental plasticity. This study was then extended towards anelasticity, or internal friction, as induced by plastic deformation and elastic-plastic strains. Plastic deformation is known to enhance internal friction loss factor, tanδ, which then leads to the so-called dislocation enhanced Snoek (DES) peak. However, the atomistic origin of DES, role of elastic versus plastic strain, has never been established. Experimental nano dynamic mechanical analysis (nano-dma) measurements were used to bring out the plasticity induced DES of near-(001) grains. Experimental DES, however, scaled with both dislocation density and residual strain. This ambiguity necessitated use of numerical simulations to decouple respective contributions. Firstly, continuum finite element simulations indicated a stronger impact of residual stress, than the total stress, on the experimental DES. Further, atomistic modeling simulated (i) single-crystal nano-dma response and (ii) corresponding developments in residual stress as well as dislocation density. In particular, the DES emerged as an attribute of the non-uniform residual strain field(s) associated with dislocation(s). The corresponding change(s) in the anisotropies of local activation energy landscape, for interstitial diffusion of carbon, determined the enhanced Snoek response. Our experiments plus numerical modeling, thus brought out, and for the first time, a unique atomistic perspective towards anelasticity induced by plastic deformation.