Effect of Stacking Fault Energy and Solute Atoms on Microstructural Evolutions of FCC Metals Processed by Severe Plastic Deformation

Abstract

Pure copper, pure silver, Cu-6.8at%Al, Cu-1at%Mn and Cu-5at%Ni (stacking fault energies (SFEs) are about 41, 22, 23, 43 and 105mJ/m2, respectively) were processed by equal channel angular pressing (ECAP) at the same homologous temperatures to investigate the effect of SFE and solute atoms on microstructural evolutions. The final grain size of Cu-6.8at%Al after eight passes of ECAP was the smallest followed by that of Cu-1at%Mn with little difference. The former alloy reaches saturation for grain size and grain boundary misorientation in early passes of ECAP while the latter continues decreasing even after eight passes. The role of shear bands and deformation twins is predominant for grain fragmentation in the early stage for Cu-6.8at%Al and Ag with low SFE while evolution from cell walls to grain boundaries is main mechanism for Cu, Cu-1at%Mn and Cu-5at%Ni with medium or high SFE. Solute Mn atom of Cu-Mn with high atomic size misfit and may suppress the dynamic recovery which transforms cell walls to grain boundaries, and allow accumulation of higher dislocations and reduction of cell size to smaller scales.