The combined effects of crystallographic orientation, stacking fault energy and grain size upon deformation twinning behavior in several face-centred cubic crystals were investigated experimentally and analytically. Three types of face-centred cubic crystals, Al single crystals, Cu single crystals and polycrystalline Cu-3%Si alloy with different stacking fault energies and special crystallographic orientations, were selected. The orientations of the Al and Cu single crystals were designed with one of the twinning systems just perpendicular to the intersection plane of equal-channel angular pressing. For Al single crystals, no deformation twins were observed after a one-pass equal-channel angular pressing, although a preferential crystallographic orientation was selected for twinning. For Cu single crystals, numerous deformation twins were found even when strained at room temperature and at low strain rate. For Cu-3%Si alloy, deformation twins were only observed in some grains; however, others with different orientations were full of dislocations, although it has the lowest stacking fault energy value of the three face-centred cubic crystal types. The experimental results provided evidence that stacking fault energy and crystallographic orientation had a remarkable influence upon the behavior of deformation twinning in face-centred cubic crystals. The observations were subsequently analyzed based upon fundamental dislocation mechanisms and the grain-size effect. The deformation conditions required for twinning and the variation in twinning stress with stacking fault energy, crystallographic orientation and grain size in face-centred cubic crystals were also considered.

Combined Effects of Crystallographic Orientation, Stacking Fault Energy and Grain Size on Deformation Twinning in FCC Crystals. W.Z.Han, Z.F.Zhang, S.D.Wu, S.X.Li: Philosophical Magazine, 2008, 88[24], 3011-29