The grain-size effect on deformation twinning in nanocrystalline Cu was studied. It was reported that deformation twinning in coarse-grained Cu occurred only under high strain rate and/or low-temperature conditions. Furthermore, reducing grain sizes was shown to suppress deformation twinning. Here, it was shown that twinning became a major deformation mechanism in nanocrystalline Cu during high-pressure torsion under a very slow strain rate and at room temperature. High-resolution transmission electron microscopy investigation of the twinning morphology suggested that many twins and stacking faults in nanocrystalline Cu were formed by partial dislocation emission from grain boundaries. This mechanism differed from the pole mechanism operating in coarse-grained Cu.

Deformation Twinning in Nanocrystalline Copper at Room Temperature and Low Strain Rate. X.Z.Liao, Y.H.Zhao, S.G.Srinivasan, Y.T.Zhu, R.Z.Valiev, D.V.Gunderov: Applied Physics Letters, 2004, 84[4], 592-4