Theoretical insight of strengthening and hardening behavior in ultrafine-grained metals under high pressure

The mechanism-based theoretical models are presented to provide the theoretical explanations for strengthening and pressure-induced hardening behaviors in ultrafine-grained metals under high pressure. The grain boundary deformation model is extended to construct the relationship among the critical stress for grain boundary deformation, pressure and the grain size. The pressure-dependent critical twinning stress is derived on the basis of dislocation theory to describe the pressure-induced hardening behavior. The classic Hall-Petch for the grain size-dependent yield strength is modified through involving the contribution of partial dislocations. The simulation results demonstrate that the proposed models provide good descriptions of the strengthening and hardening behaviors in ultrafine-grained metals with respect to the high pressure. The critical grain size for the transition of deformation mechanisms is sensitive to the pressure and the grain boundary thickness. The predicted grain size-dependent yield strength and flow stress under high pressure are agreeable well with the experimental tests. These findings could shed some lights into understanding the plastic deformations of ultrafine-grained metals under high pressure. (C) 2021 Elsevier B.V. All rights reserved.