The microstructure of near-equiatomic B2/f.c.c. FeNiMnAl alloys

A microstructural analysis of two FeNiMnAl alloys, Fe30Ni20Mn30Al20 and Fe25Ni25Mn30Al20, was performed by a combination of atom probe tomography and transmission electron microscopy techniques. Although the microstructures of both alloys, which consist of alternating platelets aligned along < 100> of the B2-ordered phase, are similar to B2/b.c.c. two-phase alloys previously observed in the FeNiMnAl system, the two phases present in the current alloys are B2-ordered and f.c.c., with the latter phase being heavily twinned. Very fine (~ 5 nm) precipitates, whose chemistry was similar to that of the f.c.c. (Fe, Mn)-rich phase, were found within the B2 (Ni, Al)-rich phase in both alloys.