Mobility of point-like defects in Cu-Al martensites

We try to define a factor, apart from temperature, which allows for the mobility of quenched-in defects in a Cu-Al system of martensitic alloys. An acoustic technique, operating for temperatures between ambient and 10 K, was applied to detect the existence of mobile quenched-in defects in alloys with Al content from 20.8 to 26.9 at.%. Mobility of quenched-in defects was not detected for alloys with Al content close to and below stoichiometric one Cu3Al, corresponding to perfect DO3 ordering. For the alloy Cu-26 at.% Al, the mobility of quenched-in defects was detected starting from temperature of around 70 K. It is suggested that the off-stoichiometry of the alloys is accommodated through anti-site defect formation on the Al deficiency side and through the vacancy formation on the Al-rich side of the phase diagram.