The influence of vacancy concentration on the mechanical behavior of Fe-40Al

In order to investigate the effect of vacancies on mechanical behavior room-temperature compression tests have been performed on polycrystals and single-slip oriented single crystals of Fe-40 at% Al annealed at different temperatures and quenched. Vacancy concentrations were determined using a combination of X-ray lattice parameter measurements and dilatometry. Both polycrystals and single crystals displayed a rapid initial increase in yield stress with increasing vacancy concentration (when [111] slip occurred on (<(1)over bar 01>) and (<(1)over bar 10>) in the single crystals), followed by a much slower increase at high vacancy concentrations (>4x10(-3)). This slower increase corresponded to the activation of (<(2)over bar 11>) slip in the single crystals. The effects of vacancies on the yield strength are consistent with a frictional strengthening mechanism. In contrast, the work-hardening rate of both polycrystals and single crystals was only weakly dependent on the vacancy concentration. Dislocation pinning points, debris and loops were produced through the interactions between gliding dislocations and the quenched-in vacancies. (C) 1997 Elsevier Science Limited.