The concentrations of quenched-in vacancies which were retained in the B2 intermetallic compound, Fe1-xAlx, were deduced, for x-values ranging from 0.39 to 0.51, from lattice-constant and density measurements after quenching from temperatures of between 773 and 1273K. The vacancy concentrations which were obtained revealed a gradual increase with composition at lower Al contents. They increased rapidly as the composition approached the stoichiometric ratio. The data for slowly cooled (1K/min) samples showed that the retained vacancy concentration was higher than that in samples which had been annealed at, and quenched from, 773K. The lattice constant for each composition decreased linearly with vacancy concentration, and this was explained in terms of an atomic size effect. Apparent vacancy formation energies were estimated from changes in the vacancy concentration with quenching temperature. The relationship between vacancy concentration and micro-hardness confirmed that there was a hardening effect due to retained vacancies. A proposed linear relationship between the hardness and the square root of the vacancy concentration was supported by the results.

M.Kogachi, T.Haraguchi: Materials Science and Engineering A, 1997, 230, 124-31