Precipitate formation in the Fe-Al-Nb and Fe-Al-Ta systems

The composition of the metastable L21 Heusler phase in Fe2AlX with (X = Nb, Ta) alloys has been determined by atom probe tomography (APT). It was found that the composition of L21 is off-stoichiometric in both systems, however closer to the stoichiometric composition in the Fe-Al-Ta than in the Fe-Al-Nb(-B) alloy. L21 dissolves faster and therefore the formation of the stable C14 Laves phase proceeds quicker in the Fe-Al-Nb(-B) alloy. Doping with boron does not lead to the formation of borides and only a slight enrichment of boron in the Fe-Al matrix at the grain boundary, which is covered with C14 precipitates is observed.