Bulk ultrafine-grained materials produced by severe plastic deformation often had low ductility. A previous study had demonstrated the possibility of lowering the stacking fault energy to simultaneously increase the strength and ductility. It was demonstrated here that there existed an optimal stacking fault energy for the best ductility in ultrafine-grained Cu–Zn alloys processed by the same severe plastic deformation processing. When the stacking fault energy was too low, the grain size lay below 15nm after severe plastic deformation processing and the stacking faults were saturated so that it was difficult to accumulate dislocations and deformation twins during the subsequent tensile testing. These results provided significant guidance for the future design of ultrafine-grained and nanocrystalline alloys for achieving high ductilities.

Determining the Optimal Stacking Fault Energy for Achieving High Ductility in Ultrafine-Grained Cu–Zn Alloys. Y.H.Zhao, X.Z.Liao, Z.Horita, T.G.Langdon, Y.T.Zhu: Materials Science and Engineering: A, 2008, 493[1-2], 123-9