Point defects in Al-Ni-Cu alloys based on the NiAl phase

A previous method of analysis of constitutional vacancies, antisite atoms and triple defects, in NiA1, is extended to the ternary Al-Ni-Cu field of this phase. Because its affinity for Al is smaller than is that of Ni, Cu is able to transfer more abundantly than Ni, by thermal activation, from the Ni-sublattice to antisite positions in the Al-sublattice. The distribution of vacancy content across this ternary field is then shown to follow from the effects of configurational entropy. The presence of constitutional defects in the non-stoichiometric alloys (i.e. Al not equal 50 at%) reduces the entropy gain from the thermal formation of Cu-based triple defects and thereby diminishes the effectiveness of the Cu as a producer of additional vacancies.