The relationship between point defects and mechanical properties in FeAl at room temperature

Abstract

The defect concentrations and mechanical properties of B2-structured FeAl have been investigated at room temperature as a function of Al concentration. Mechanical testing of large-grained FeAl alloys has shown that the yield strength decreases rapidly with small (iron-rich) deviations from the stoichiometric composition but is almost independent of composition from 40 to 45 at.% Al. X-ray diffractometry was used to determine the lattice parameter, the degree of long range order, the concentration of vacancies and the fraction of lattice sites occupied by anti-site atoms. It was found that the lattice parameter increases with increasing Al concentrations for Fe-rich and stoichiometric compositions, but that the lattice parameter of Fe-51 at.% Al is almost the same as that of Fe-50 at.% Al, indicating that one FeAl phase boundary is around the stoichiometric composition. The anti-site atom concentrations are shown to decrease and the vacancy concentration to increase with increasing Al content. Comparisons of the anti-site atom concentration and vacancy concentration with the yield strength as a function of Al concentration suggest that vacancies control the room temperature mechanical properties.