Microstructural Evolution and Deformation Mechanisms in Fe-Mn-Al-Ni-C Compositionally Complex Steels

Abstract

The development of advanced lightweight steels is critical for energy conservation and the reduction of emissions. This paper outlines the application of high-entropy alloy (HEA) design principles to the traditional Fe-Mn-Al-C system, resulting in a novel class of Compositionally Complex Steels (CCSs). By incorporating five principal elements, the alloy accesses a unique dual-nanoprecipitation phase space, enabling the simultaneous formation of ordered κ-carbides and B2 intermetallic compounds. This paper details the microstructural evolution and deformation mechanisms of the CCS across a spectrum of mechanical loading conditions. At room temperature, the synergistic interplay of dislocation shearing and bypassing within the dual-nanoprecipitation enhances the flow stress to an extent that triggers high-stress mechanical twinning, overriding the limitations of the inherently high stacking fault energy of lightweight steels. Furthermore, we evaluate the microstructural evolution under extreme conditions: dynamic high-strain-rate loading induces intricate multidirectional twinning networks and localized amorphization, while cryogenic deformation triggers an unprecedented paradigm shift from Orowan bypassing to the direct dislocation shearing of brittle B2 intermetallics. These findings provide valuable insights into designing ultra-strong, damage-tolerant structural materials.