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 Fe 40 Mn 40 Co 10 Cr 10 , Fe 39.5 Mn 40 Co 10 Cr 10 C 0.5 , and Fe 38.3 Mn 40 Co 10 Cr 10 Mo 1.7 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 ε-martensite with strain in Fe 38.3 Mn 40 Co 10 Cr 10 Mo 1.7 at 77 K. The fractions of annealing twins played important roles in the nanostructural evolution and grain refinement of the Fe 38.3 Mn 40 Co 10 Cr 10 Mo 1.7 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 (ΔGfcc−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 Fe 39.5 Mn 40 Co 10 Cr 10 C 0.5 exhibited an excellent strength/ductility combination (1022 MPa/~ 110%) at 77 K. • Effects of C and Mo on the nanostructural evolution and deformation were studied. • Deformation is dependent on changes of SFE, friction stress & ΔG fcc−hcp by alloying. • TRIP effect is stimulated by addition of Mo in Fe 40 Mn 40 Co 10 Cr 10 high entropy system. • Combined TWIP/TRIP in Fe 39.5 Mn 40 Co 10 Cr 10 C 0.5 enhanced both strength/ductility at CT. • Superior mechanical properties achieved via metastability engineering at CT.