Relationship between extrinsic stacking faults and mechanical twinning in F.C.C. solid solutions with low stacking fault energy

A detailed analysis of twin nucleation and growth is performed for the case of face-centred cubic materials with low stacking fault energy γ. It is found that twin nucleation may occur only if certain conditions concerning the crystallographic orientation, sign of the applied stress and deformation level, are satisfied. Each of these conditions is analysed ; their interdependence leads to the conclusion that the occurrence of twinning is controlled by the nucleation and the growth of extrinsic stacking faults. This analysis concentrates on cases where the tensile (or compressive) axis is either [100] or [111]. The discussion of the energy of twin nucleation leads to a quantitative relation between twin size and stacking fault energy γ. These assumptions are in good agreement with experimental data on many face-centred cubic solutions.