Determining the optimal stacking fault energy for achieving high ductility in ultrafine-grained Cu–Zn alloys

Bulk ultrafine-grained (UFG) materials produced by severe plastic deformation (SPD) often have low ductility. A previous study demonstrated the possibility of lowering the stacking fault energy to simultaneously increase the strength and ductility. This paper demonstrates, there exists an optimal stacking fault energy for the best ductility in UFG Cu–Zn alloys processed by the same SPD processing. When the stacking fault energy is too low, the grain size lies below 15 nm after SPD processing and the stacking faults are saturated so that it is difficult to accumulate dislocations and deformation twins during the subsequent tensile testing. These results provide significant guidance for the future design of UFG and nanocrystalline alloys for achieving high ductilities.