Excellent work hardening ability in a novel compositionally complex alloy by hierarchical microstructuring

•A compositionally complex Fe44Mn20Cr15Ni7.5Co6Si7.5 alloy (M-CCA) exhibits exceptional strength (867 MPa) and elongation to failure (110 %) synergy at room temperature owing to its hierarchical type heterostructure formed after thermo-mechancial processing and adaptive activation of deformation mechanisms.•Exceptional work hardening is the result of hetero-deformation induced (HDI) strengthening in early stage of deformation whereas planar slip assisted hetero-deformation banding, and deformation twinning in later stages of deformation during plastic straining.•The high strength-ductility index (SDI) for M-HEA is ∼512 MPa and uniform elongation ∼82 %, suggests its desirability for various safety-critical application in automotive, oil and gas, nuclear, and structural industries owing to its high energy storage capacity and crash worthiness. Strength and ductility vary inversely due to a rapid decrease in dislocation storage capacity with the pronounced increase in work hardening rate at the expense of ductility in most conventional and recently designed advanced ductile materials. This limitation can be overcome by creating heterogenous or hierarchical microstructures containing not only presence but also different length scales of twins, bands, phases synergistically. In line of that, here we present Fe44Mn20Cr15Ni7.5Co6Si7.5 (all in at.%) compositionally complex alloy (M-CCA), which showed an exceptional increase in strength and ductility simultaneously as a result of hierarchical microstructuring that forms after conventional thermo-mechanical treatment. The increase in strength-ductility synergy is attributed to the occurrence of hetero-deformation induced (HDI) strengthening in early stage of deformation whereas planar slip assisted hetero-deformation banding, and deformation twinning in later stages of deformation during plastic straining. Hence, hierarchical microstructuring in M-CCA resulted in exceptional work hardening ability which is needed for structural integrity and manufacturing applications under tensile loads to suppress sudden failures during service. [Display omitted]