Simultaneous Twinning and Microband-Induced Plasticity of a Compositionally Complex Alloy with Interstitial Carbon at Cryogenic Temperatures

Intermediate to low stacking fault energy (SFE) high entropy alloys (HEA) have shown an excellent combination of strength and ductility as a result of deformation twinning and martensite transformation. However, even in the absence of these mechanisms HEA can show a good strength-ductility combination, as is the case with non-equiatomic (Fe40.4Ni11.3Mn34.8Al7.5Cr6)C1.1. The room temperature mechanical behavior of this alloy has been associated with Taylor lattice and microband formation. The current research focuses on tensile cryogenic deformation of this alloy and investigates if these features and/or alternate mechanisms like deformation twinning are obtained. Surprisingly, it is not one or the other but both deformation twinning and microband formation that are observed during cryogenic deformation. The activation of both deformation mechanisms is a combination that is not often reported as the former is generally associated with intermediate to low SFE alloys and the latter with intermediate to high SFE alloys. The activation of twinning in (Fe40.4Ni11.3Mn34.8Al7.5Cr6)C1.1 is attributed to the high yield stress-temperature variation, as a result of solid solution strengthening being far greater than in other commonly researched compositionally complex alloys. A ductility retention down to 4 K was observed, while simultaneously showing a significant increase in flow stress. Despite the intermediate to high SFE deformation behavior, (Fe40.4Ni11.3Mn34.8Al7.5Cr6)C1.1 exhibits excellent cryogenic strength-ductility combination.