A New Model That Considers the Gradual Change in Local Crystalline Geometry to Account for Grain Boundary Hardening

Abstract

In this study, a new model is proposed to account for grain boundary hardening. The gradual change in the local crystalline geometry constrained by grain boundaries, where dislocations glide and are stored within polycrystalline grains during plastic deformation, is considered by subdivision of the grains in the form of crystalline strips. Within this context, the local dislocation densities, corresponding local strengths, and even the local strains developed within polycrystalline grains could be computed for each crystalline segment for a given small amount of plastic strain. For this purpose, the Orowan equation was implemented together with Taylor polycrystalline deformation and Taylor hardening models. It was also assumed that, rather than strain, the deformation within polycrystalline grains is controlled by stress. Based on these, a new model was developed. The model was verified by comparing the predicted results with the experimental results found in the literature for several pure face centered cubic (FCC) materials, and a good agreement was found. In addition, based on the current model, three alternative equations were also derived to compute yield strength in terms of plastic strain and the reciprocal of grain size. Nevertheless, the model proposed in this study provides new insights in terms of understanding grain boundary hardening.