On the behaviour of mechanical twinning in Cu-Al single crystals

This work brings experimental observations on 295 and 77.4 K necking and twinning phenomena occurring at the end of overshoot in Cu-Al single crystals tested in tension. Critical concentrations of aluminium for a transition of overshoot necking → overshoot twinning to occur were found. It was also found that the disappearance of load drops which usually accompany mechanical twinning of more dilute alloys is controlled by critical solute concentration. A simple explanation of both types of transition which is based on γ/b criterion has been suggested. Strengthening of F.C.C. materials due to mechanical twinning is also discussed.