A new class of non-equiatomic FeNiCoAlTaB (NCATB) high entropy alloy (HEA) is introduced, which exhibits tunable properties from cryogenic/ambient superelasticity to ultra-high strength through controlling the nature or type of martensite. In the current NCATB-HEA alloy system, depending on the size of γ'-Ni 3 Al (L1 2 ) precipitates, thin-plate, lenticular, butterfly, and lath-like martensite can form. When thin-plate thermoelastic martensite is favored, a superelastic strain of about 0.025 (ambient) and %0.01 (cryogenic) is achieved with a high yield stress of %800 MPa and a high-damping effect (10 times higher than Cu-Al-Ni superelastic alloy). While for butterfly and lath-like martensite dominated NCATB-HEA, an ultra-high yield stress of around 1.1 GPa is achieved while no superelasticity is demonstrated. This current alloy system helps to expand the application domain of HEAs, for example, into high-damping applications, robust actuators, space exploration, and other structural material applications.

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