Effects of carbon and molybdenum on the nanostructural evolution and strength/ductility trade-off in Fe₄₀Mn₄₀Co₁₀Cr₁₀ high-entropy alloys

The effects of carbon and molybdenum on the strain-induced nanostructural evolution and strength-ductility trade-off in Fe40Mn40Co10Cr10, Fe39.5Mn40Co10Cr10C0.5, and Fe38.3Mn40Co10Cr10Mo1.7 high-entropy alloys (HEAs) were investigated at room temperature (RT) and cryogenic temperature (CT). Deformation twinning was the dominant deformation mechanism for all the three HEAs at RT. The addition of Mo enhanced the metastability and thus increase the volume fraction of epsilon-martensite with strain in Fe38.3Mn40Co10Cr10Mo1.7 at 77 K. The fractions of annealing twins played important roles in the nanostructural evolution and grain refinement of the Fe38.3Mn40Co10Cr10Mo1.7 at CT. The nanostructural evolution was found to be controlled by modifying SFE, the friction stress for cross slip and Gibbs free energy for phase transformation (Delta Gfcc-hcp) via alloying with Mo or C. The nucleation of mechanical twinning at RT and the preferential occurrence of strain-induced martensitic transformation at CT was found to induce the grain partitioning through the hierarchical structure formation and enhanced work hardening rate. The simultaneous occurrence and synergistic effect of twinning-induced plasticity/transformation-induced plasticity in Fe39.5Mn40Co10Cr10C0.5 exhibited an excellent strength/ductility combination (1022 MPa/similar to 110%) at 77 K. (c) 2022 Elsevier B.V. All rights reserved.