Deformation twinning in alloys at low temperatures

Observations on low temperature mechanical twinning in Cu and Cu-Zn alloys are reported. The absence of indications of twinning on the stress-strain curves of crystals of 70:30 α-brass is discussed in relation to recent preliminary electron microscopy observations. The twinning data are consistent with the existence of a critical twinning stress which decreases with decreasing stacking-fault energy. The results are discussed in terms of recent models for twinning in f.c.c. crystals.