Effect of Stacking Fault Energy on the Microstructural Evolution of Pure Cu and Cu-Al Alloys during Severe Plastic Deformation

Pure Cu and Cu-Al alloys with different stacking fault energies (SFEs) were processed by severe plastic deformation (SPD) methods to systematically explore the roles of the SFE in microstructure evolution. With a lowering of the SFE, the deformation mechanisms were gradually transformed from dislocation slip to deformation twins while shear bands were increasingly significant to carry the local plasticity. Concurrently, with decreasing SFE, the grain refinement processes were also transformed from dislocation subdivision to twin fragmentation, while the grain size was refined from the ultrafine region into nanoscale. Furthermore, the homogeneous microstructures are more readily achieved in materials with high or low SFE than in materials with medium SFE due to different mechanisms governing the microstructural evolution. Specifically, recovery processes are dominant in high or medium-SFE materials whereas twin fragmentation is dominant in low-SFE materials.