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

Abstract

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.

Keywords:

• copper
• Cu–Al alloys
• stacking fault energy
• high-pressure torsion
• hardness
• homogeneity

Acknowledgements

The authors thank Professor J.T.M. de Hosson, Professor J.D. Embury and Professor Y. Brechet for stimulating discussions. This work was supported by the Innovation Fund for Graduate Students of IMR.CAS and the National Natural Science Foundation of China (NSFC) under grant Nos. 50625103, 50841024, 50890173 and 50931005, the National Basic Research Program of China under grant No. 2010CB631006 and the Royal Society of the UK under International Joint Project No. JP871294.