On the activation of alternated stacking fault pair twinning mechanism in a very large-grained Fe–29Mn–2.4Al steel

Abstract An alternated stacking fault (SF) pair twinning mechanism involving local fcc → hcp transformation in a very large-grained high-Mn austenitic steel is reported, which hitherto was valid for nano crystalline metals. It was identified using high-resolution transmission electron microscopy that a pre-twinned e-martensite like phase, containing local hcp structure is converted to a stable three-layer twin lamella through nucleation of new SF in-between the pre-existing SFs. Activation of observed mechanism is deciphered in terms of the low intrinsic and unstable stacking fault energies ratio of the steel (~ 0.13), predicted using a model based on density functional theory.