The annealing of vacancy defects in β-NiAl I. Vacancy loop growth in as-grown single crystals annealed in ultra-high vacuum

Abstract

Abstract Annealing studies have been performed in ultra-high vacuum on thinned samples taken from as-grown single crystals of β-NiAl. The resultant climb of vacancy dislocation loops has been observed using transmission electron microscopy. Dislocation loops grow during annealing at temperatures between 650–700°C, but the growth rate tends to zero after annealing for 2 hours at 700°C. The results of these experiments are consistent with the view that a relatively large supersaturation of vacancies is retained in crystals, presumably trapped at impurity atom or present in the form of clusters, during cooling from the melting point. Such an explanation implies a low value for the energy of formation of vacancies. This is deduced in the present paper from the results of quenching experiments, where it was found that the energy of formation E t of a pair of vacancies is 1·45 ± 0·2 eV.