Martensitic Phase Transformation in a f.c.c./B2 FeNiMnAl Alloy

Fe36Ni18Mn33Al13 is a lamellar two-phase alloy comprising a hard, Ni,Al-rich B2 phase measuring ~500 nm in width and a ductile, Fe,Mn-rich f.c.c. phase ~1 µm in width. Upon cold rolling and annealing, the as-cast microstructure is replaced by discrete, recrystallized ~1 µm-sized grains consisting of the f.c.c. phase and a 7R (14 M) martensite phase. The formation of the latter phase appears to be related to the change in composition of the phases upon recrystallization. Room-temperature tensile tests performed on 50 % cold-worked and annealed Fe36Ni18Mn33Al13 reveal that complete recrystallization does not occur until after 24 h of annealing at 900 °C, wherein the yield strength and elongation to fracture of the recrystallized alloy are ~443 MPa and 21 %, respectively—a change from the as-cast alloy’s values of ~352 MPa and ~28 %.