Significance of strain rate in severe plastic deformation on steady-state microstructure and strength

The microstructure and mechanical properties of materials saturate to steady states after severe plastic deformation (SPD). Despite the well-known effect temperature on steady-state microstructure, there is no general agreement significance strain rate applicability Zener-Hollomon parameter in this regard. In study, several pure metals (aluminum, copper, titanium, iron) a Cu–30Zn (wt%) brass alloy have been processed by high-speed high-pressure torsion (HPT) equipment with controllable rotation speeds range 0.06–60 rpm. It found that crystallite/grain size, dislocation density, microhardness shear stress at state are reasonably rate-independent for von Mises rates 0.004–20 s−1. Because both grain refinement dynamic recrystallization proportional rate, it suggested their balance, which determines state, rate-independent.