Multifunctional Non‐Equiatomic High Entropy Alloys with Superelastic, High Damping, and Excellent Cryogenic Properties

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.