Thermal and mechanical disordering of ordered alloys

Abstract

The structure of ordered compounds and antiphase boundaries (APBs) is of interest both for fundamental study of phase changes and because these features affect the faults contained within dislocations that will determine their mobility, and hence affect mechanical properties. General ideas of order and chemical relaxation at APBs seem to be well established, with thermal disordering occurring by the appearance of disorder at APBs and also by disorder appearing uniformly throughout the domains. That mechanical disordering occurs by partial or imperfect dislocations trailing defects seems a reasonable idea. It is difficult to decide, however, which are the specific defects that accumulate to lead to mechanical disordering. Several examples of thermal and mechanical disordering will be presented. Special attention will be given to relaxation/disordering processes at APBs during annealing, and in particular the role of off-stoichiometry from the ideal composition. The disordered structure produced by plastic deformation will be examined, considering high resolution electron microscope studies as well as some measurements of physical properties, that make it possible to deduce how disordering occurs.