An investigation of vacancy-like defects in stoichiometric NiAl by means of positron annihilation measurements

Abstract

Vacancy-like defects in stoichiometric NiAl are investigated by means of positron lifetime and Doppler-broadening measurements after quenching from high temperatures and proton or electron irradiation. The lifetime of the annealed samples, τ=178 ps, confirms that remnant defects, most probably vacancies and vacancy complexes, are quenched-in during the production of the samples. The decrease of the positron lifetimes and the S-parameter values with increasing quenching temperature are explained with the increasing concentration of Al vacancies. The isochronal annealing of the samples, quenched from 1600°C, shows a distinct agglomeration of defects in the temperature range 400–800°C. After proton and electron irradiation no change in the positron lifetime is observed. There is an annealing stage in the temperature range 900–1200°C. The S-parameter after proton irradiation shows an additional annealing step at around 200°C. Long-time annealing for 520 h at 1150°C does not result in a remarkable reduction of the positron lifetime.