Vacancies effect on the mechanical properties in B2 FeAl intermetallic by the first-principles study

The geometric structures, electronic and mechanical properties of the high vacancy concentration intermetallic FeAl (experimental value: 3.3 at.% at 1451 K) were investigated by first-principles calculations based on density functional theory. The FeAl structures of different vacancy concentration with minimum energy were addressed, which shows that vacancies of iron (V-Fe) are more favourable and tend to gather together. For mechanical properties, both Young's modulus and elastic constants show an overall downward trend as vacancy concentration increases, but increase abnormally with the vacancy concentration ranging from 3.7 at.% to 5.6 at.%. All can be explained by the strength of Al-Fe bond, in other words, the Al-Fe interaction. Interestingly enough, intermetallic FeAl shows a transfer from the brittle manner to ductile manner, which also behaves as an important feature of FeAl in experiments. All the mechanical properties agree well with experimental data, indicating the reasonable vacancy model of FeAl intermetallic.