Structure of point defects in B2 Fe-Al alloys : An atomistic study by semi-empirical simulation

We present the first results of a simulation study of point-defect properties in B2 ordered Fe-Al alloys (34% < x Al < 52%). After examining the T = 0 K energetics of simple defects, we turn to complexes and discuss the usual hypothesis of independent elementary defects. Almost all complex defects involving an Al vacancy and an Al antisite atom in nearest neighbour position are shown to be unstable, confirming that Al vacancies are rare in these alloys. Small deviations from stoichiometry induce a change in the nature of defects: whereas on the Al-rich side, isolated Al antisite atoms dominate, Fe antisite atoms have a strong trend towards clustering on the Fe-rich side, leading to the formation of local D0 3 order.