Introducing strain glass transition into high-entropy TiZrHfNiCuCo alloys exhibiting elastocaloric effect and quasi-linear superelasticity

High entropy alloys (HEAs) have garnered significant attention due to their vast compositional space and tremendous potential for advanced structural and functional properties. While most studies on HEAs concentrate on optimizing one or two primary characteristics, there exists a transformative opportunity in designing HEAs that integrate multiple structural and functional attributes. In this work, we present equiatomic TiZrHfNiCuCo HEAs that exhibit a remarkable combination of mechanical and functional properties, including high strength, low elastic modulus, quasi-linear superelasticity, broad-temperature-range elastocaloric effect with a high coefficient of performance (COP_material) spanning from 223 K to 423 K, elastic modulus softening, and exceptional fatigue stability exceeding 10⁵ cycles. Through detailed nanoscale microstructural analysis, we demonstrate that these properties are linked to the strain glass transition in the HEAs, characterized by frequency-dependent modulus behavior, invariance of average structure, non-ergodicity, and the formation and growth of nanodomains. The high COP_material elastocaloric effect, and long-term fatigue stability can be attributed to the quasi-linear superelasticity with narrow hysteresis that originates from the stress-induced continuous evolution of nanodomains. The elastic modulus softening arises from the combined contributions of the elastic modulus softening of the B2 matrix and the elastic modulus hardening of B19′ and R nanodomains, as well as other precipitates. Our work sheds light on the strategy to introduce strain glass transition into advanced HEAs for designing structural and functional properties.