Effect of strain hardening on subgrain formation during ECAP process

Abstract

The effect of strain hardening on the grain refinement in the Equal Channel Angular Pressing (ECAP) is studied by applying various hardening models and the ratio of the latent hardening to self-hardening in the form of the latent hardening matrix in the elasto-viscoplastic material model. The initial and final orientations of pure nickel single crystals after a single pass are evaluated to study subgrain formation during the ECAP extrusion. The pole figures show that all hardening models predict almost the same trends in the grain refinement as observed in experiments. The results demonstrate that with increasing latent hardening ratios the orientations are heterogeneously scattered around the initial orientation. Also the analysis of the misorientation distribution reveals that the grain fragmentation has occurred with both high and low angle grain boundaries. The reconstruction of the microstructure after the deformation shows that when the active and latent slip systems harden equally, the number of subgrains is minimum, and with increasing latent hardening ratios (the active systems harden faster than other systems) the number of subgrains is increasing.