Steady-state characteristics of fcc pure metals processed by severe plastic deformation: experiments and modelling

A series of experimental studies are carried out to investigate the steady-state microstructures and mechanical properties of Cu, Ni, and Al obtained by equal-channel angular pressing (ECAP) at homologous temperatures. Under 0.32T(m) the steady-state grain sizes d(s) of the three metals are below 1 ?m, and dominated by dynamic recovery mechanism. Discontinuous dynamic recrystallization (DDRX) occurs in Cu and Ni processed by ECAP at 0.4T(m). The variation of dislocation density at 0.32T(m) (?(Cu)>?(Ni)>?(Al)) shows a dependence on stacking fault energy (SFE), and it is consistent with the change of kernel average misorientation (KAM) values (Cu?>?Ni?>?Al). The SFE not only influences the strain hardening capacity of metals but also the critical strain needed to get steady-state. In order to understand the relationship between SFE and d(s) quantitatively, a steady-state grain size model based on the Mohamed?s dislocation model is proposed through considering dynamic recovery mechanisms. Two important factors temperature and SFE are involved in the model, and other parameters and constants are determined from our experimental data. The predictions of d(s) by the model are compared with d(s) obtained by experiments for five fcc pure metals (Au, Ag, Cu, Ni, and Al), and the characteristic and limitation of the model are discussed.