It was recalled that, at high temperatures, FeAl generated a large number of thermal vacancies, and their concentration increased with increasing Al content. Heat treatment, temperature, and time controlled the vacancy concentration. An increasing vacancy concentration increased the hardness and decreased the ductility. The increasing yield strength with increasing temperature was believed to be due to vacancy hardening, and a decrease in strength above the peak temperature was attributed to creep. Ternary alloying elements, except B, had little effect upon the hardening at high temperatures and could increase the hardness after long-term annealing at low temperatures. This review presented a summary of the current literature available on FeAl vacancies and their effects, including: hardness, yield strength anomaly, and the effect of ternary alloying elements.

Vacancy Formation and Effects in FeAl. J.L.Jordan, S.C.Deevi: Intermetallics, 2003, 11[6], 507-28