In this study, the Fe-16Mn-9Al-0.8C-3Ni (wt.%) lightweight steel was fabricated by novel twin-roll strip casting technology. The microstructure, tensile properties and strain-hardening behavior of the present steel have been investigated and compared to those of conventionally processed steels with similar chemical compositions. After annealing, a unique gradient microstructure of intermetallic compound (B2)-austenite was obtained along the thickness direction, consisting of granular B2 (average: 430 nm) and fine austenite (average: 1.82 μm) at the surface layer, blocky B2 (average: 1.03 μm) and medium austenite (average: 3.98 μm) at the quarter layer and polygonal B2 (average: 1.94 μm) and coarse austenite (average: 6.13 μm) at the center layer. The cooperative action of B2 pinning dislocation, plane slip and back stress led to stronger strain hardening, among which the strong back stress effect originated from the multistage discontinuous austenite deformation and the mechanical incompatibility between austenite and B2 is believed to be the most important reason, thereby achieving an excellent balance of strength (ultimate tensile strength: 1147 MPa) and ductility (total elongation: 43.2%). This work not only developed a new processing way to fabricate Ni-containing Fe-Mn-Al-C lightweight steel with outstanding mechanical properties, but also provided a potential solution for manufacturing some other metallic materials accompanied by brittle B2 intermetallic.

High-temperature heat treatments can improve the element distributions and phase structures of AlCoCrFeNi high entropy alloys (HEAs). However, the long-term isothermal annealing at high temperatures will make the grains grow crazily. In this study, the problem of grain growth caused by high-temperature annealing at 1200 °C was solved by heavily deformed AlCoCrFeNi HEAs. The ultrafine grains formed by dynamic recrystallization will grow firstly during the subsequent annealing process, which inhibits the increase in the larger grains in the hot-extruded AlCoCrFeNi HEAs. The effect of high-temperature annealing on hot-extruded AlCoCrFeNi HEAs was also explored simultaneously in detail. After annealing at 1200 ℃ for 2 h, the compressive strength and fracture strain of the AlCoCrFeNi HEA reached an astonishing result of 3750 MPa and 43%, respectively. The results are attributed to the skeleton-liked FCC structures deeply interspersed into the grains and more importantly, the fine annealed grains which still maintained an average diameter of 20 μm. Additionally, the new nano-precipitates did not expand wildly at high temperatures either. Research on heavily deformed AlCoCrFeNi HEAs isothermally annealed at 1200 °C provides an available idea for further improving the properties of these HEAs.

The mechanical properties of the AlCoCrFeNi high-entropy alloy (HEA) can be significantly enhanced by grain refinement. However, it is difficult to refine the grain size of AlCoCrFeNi HEA by solidification methods. In this study, fine-grained AlCoCrFeNi HEA was successfully prepared by heavy thermal mechanical processing. The AlCoCrFeNi HEA consists of FCC, B2, and BCC phases. The FCC phase is distributed on grain boundaries, while the B2 phase is embedded in the BCC matrix within the grains. The fine-grained AlCoCrFeNi HEA has enhanced strength and ductility compared with its coarse-grained counterpart. The enhanced strength–ductility synergy of the fine-grained AlCoCrFeNi HEA is attributed to three key factors: the fine-grained microstructure, the delayed initiation of cracks within the hard-to-deform grain matrix, and the impediment of crack propagation by the grain boundaries enriched with the FCC phase.