Deformation-induced multi-step TRIP/TWIP(fcc, hcp) behaviors in metastable Fe55Mn25Co10Cr10 high-entropy alloy at ambient and cryogenic temperatures

Abstract

The mechanical performance and multi-step TRIP/TWIP behaviors in a metastable Fe55Mn25Co10Cr10 were systematically investigated at room temperature (RT) and 77 K. The deformation behaviors and mechanically induced 8-martensite, fcc twin and hcp twin bands in Fe55Mn25Co10Cr10 were studied based on the thermodynamics and nanostructural analyses. Deformation-induced nanostructural evolutions were found to vary greatly as the temperture decreases from RT to 77K. Deformation induced 8-martensite and fcc deformation twins (fcc) carrying more strain developed at RT. On the other hand, bi-directional 8-martensite bands were favored to accommodate the increased strain at 77K instead of fcc deformation twins because of the increased stability of hcp phase. Complicated hcp 8-martensite twins developed adjacent to the crossed region of two 8-martensitec bands at 77K. The tensile stress developed perpendicular to the original hcp 8-martensite band because of its intrinsic smaller c/a ratio (1.615-1.620) than the ideal ratio (1.633) in hcp 8-martensite, inducing {10I<overline>2} twins with (0001) basal plane approximately perpendicular (86.0 degrees) to that of the original 8-martensite band. Hcp twinning in the 8-martensite band at 77K is suggested to be driven by the structural and electronic relaxations associated with the c/a distortion of the hcp 8-martensite bands. Excellent strength-ductility combinations were also obtained at RT (861MPa/73.2 %) and 77 K (1.42GPa/61.8 %) because of the enhanced hardening rates due to TRIP/TWIP(fcc) at RT and/or TRIP/TWIP(hcp) at 77 K in this study.