Vacancy-like defects in stoichiometric material were investigated by means of positron lifetime and Doppler-broadening measurements after quenching from high temperatures and after proton or electron irradiation. The lifetime (178ps) in annealed samples confirmed that remaining defects, which were probably vacancies and vacancy complexes, were quenched-in during production of the samples. Decreases in the positron lifetimes and the S-parameter values, with increasing quenching temperature, were explained in terms of an increasing concentration of Al vacancies. Isochronal annealing of samples which had been quenched from 1600C revealed a distinct agglomeration of defects at temperatures ranging from 400 to 800C. No change in the positron lifetime was observed after proton or electron irradiation. There was an annealing stage between 900 and 1200C. The S-parameter after proton irradiation exhibited an additional annealing step at about 200C. Long-term annealing (1150C, 520h) did not result in any marked reduction in the positron lifetime.

An Investigation of Vacancy-Like Defects in Stoichiometric NiAl by means of Positron Annihilation Measurements. W.Puff, B.Logar, A.G.Balogh: Acta Materialia, 1999, 47[1], 101-9