Abstract Three copper-gold single crystals containing 29.9 at. % gold and having the disordered, Cu3Au I and Cu3Au II structure respectively, were deformed in tension at room temperature, at dry ice temperature (just into the plastic region) and at liquid nitrogen temperature (until fracture) successively.
For Cu3Au I and Cu3Au II 00 does not vary practically with composition, being four times that of stoichiometric Cu3Au . At 78° K twinning was observed in the elastic region for Cu3Au II, whereas Cu3Au I twinned only under the influence of complex stresses; the disordered alloy showed no twinning at all.
The strain-hardening II at 78° K is almost the same for Cu3Au I and Cu3Au II at the 20.9 at. % composition.