Thermal formation of atomic vacancies in Ni3Al

Transition-metal aluminides are of interest both from the viewpoint of basic research and with respect to their potentials for technical application as high-temperature materials.(1,2) The investigation of the formation and migration of atomic defects is a prerequisite for the understanding of self-diffusion processes,(3) order-disorder phenomena,(4) creep behavior,(5) mechanical hardening,(6) or plastic deformation, Positron lifetime spectroscopy is a sensitive and specific technique for studying thermal vacancy formation in pure metals(8) as well as in intermetallic phases. (9-17) For a detailed understanding of the experimental data on thermal vacancy formation in ordered intermetallic compounds a theoretical treatment of thermal defect formation in the framework of ab initio calculations,(7,18) embedded-atom calculations,(l9'20) or empirical nearest-neighbor bond models(21-29) is necessary. A comprehensive overview of the systematics of thermal defect formation, migration, and self-diffusion in intermetallic compounds and ordered alloys was given recently,(30) The present work aims at the investigation of the thermal vacancy formation in Ni3Al in dependence on temperature and composition by positron lifetime spectroscopy accompanied by model calculations based on the interaction of nearest-neighbor atoms.