Significance of stacking fault energy on microstructural evolution in Cu and Cu-Al alloys processed by high-pressure torsion

Disks of pure Cu and several Cu-Al alloys were processed by high-pressure torsion (HPT) at room temperature through different numbers of turns to systematically investigate the influence of the stacking fault energy (SFE) on the evolution of microstructural homogeneity. The results show there is initially an inhomogeneous microhardness distribution but this inhomogneity decreases with increasing numbers of turns and the saturation microhardness increases with increasing Al concentration. Uniform microstructures are more readily achieved in materials with high or low SFE than in materials with medium SFE, because there are different mechanisms governing the microstructural evolution. Specifically, recovery processes are dominant in high or medium SFE materials, whereas twin fragmentation is dominant in materials having low SFE. The limiting minimum grain size (d(min)) of metals processed by HPT decreases with decreasing SFE and there is additional evidence suggesting that the dependence of d(min) on the SFE decreases when the severity of the external loading conditions is increased.