Characterization of cold-rolled heterogeneous microstructure formed by multimodal deformation in an Fe-Ni-Al-C alloy with lattice softening

A heterogeneous microstructure in cold-rolled Fe-24.1Ni-4.06Al-0.43C with lattice softening, where C'=(C-11-C-12)/2 is significantly reduced, was investigated through hierarchical analysis from the macroscale to nanoscale to determine the origin of the ultrahigh-strength and large ductility of the alloy. Microstructural analysis revealed that the heterogeneous microstructure in the developed Fe-based alloy exhibited a mixture of four kinds of morphology, formed through different deformation processes activated by the specific phase stability with lattice softening which arises at the limit of phase stability of austenite (fcc) phase. In addition to the reduced C', the alloy is also characterized by the lowered stacking fault energy (SFE) and decreased the austenite-to-martensite (Ms) transformation temperature down to ambient temperature. These results suggest that both deformation twinning and stress-induced martensitic transformation are activated simultaneously or successively, in addition to dislocation glide, during cold rolling in the present alloy. On the basis of microstructural and mechanical characterization of the cold-rolled specimen, it is reasonable to conclude that the work-hardening induced by cold rolling activates a multimodal deformation mechanism which suppresses the premature failure during plastic deformation at ultrahigh-strength. (C) 2018 Elsevier Ltd. All rights reserved.