Effects of stacking fault energy and solute atoms on microstructural evolution of Cu, Ag and Cu–Al alloys processed by equal channel angular pressing

Abstract

The effect of alloying elements on microstructural evolution during the formation of ultrafine grained (UFG) structures in fcc materials during equal channel angular pressing (ECAP) was investigated. This research focused on the relative influence of stacking fault energy (SFE) and solid solution effect by comparing Cu, Ag and Cu–Al alloys (Cu-4.6 at%Al and Cu-6.8 at%Al). Either the dislocation cell or grain sizes were found to decrease together with a significant accumulation of dislocations during the early stage of successive passes in materials having low SFEs. These changes occurred regardless of the presence of solute atoms. In contrast, the solid solution effect resulted in delayed saturation of the dislocation density and hardening in the later stage of deformation, at which point the formation of a UFG structure was almost complete. The grain size after eight passes decreased with decreasing SFE, following a power law relationship. However, the effect of solute atoms on grain size reduction increased at greater plastic strain values because of steady, ongoing microstructural evolution and hardening resulting from the solid solution effect.