Achieving wide temperature range superelasticity in additively manufactured high-entropy alloys via refined composite microstructures and partial strain glass transition

Superelastic alloys for critical applications in extreme environments are required to combine a wide operating temperature range, low temperature sensitivity, and high strength. Achieving this combination is challenging. Drawing from high-entropy and superelastic alloy design principles, this study utilised laser-directed energy deposition (L-DED) to fabricate TiZrHfNiCu high-entropy superelastic alloys with excellent forming quality. The intricate composition and swift solidification conditions resulted in a uniform, fine, and isotropic dendritic microstructure within this high-entropy alloy, which comprises the B2 phase, B19’ phase, and Zr₂Cu-like phase. In comparison to the as-cast material, the LDED-TiZrHfNiCu material exhibits a reduced degree of component segregation and concurrently experiences strain glass transition alongside martensitic crystallisation behaviour. The alloy demonstrated recoverable superelastic strains exceeding 5%, a fracture strength over 2 GPa, and very low temperature sensitivity between 173 K and 473 K. Additionally, this method addresses the difficulties associated with machining superelastic alloys and the challenges associated with manufacturing complex geometries. This study illustrates the fabrication of TiZrHfNiCu alloy via L-DED, offering a new perspective on the preparation of high-strength, wide-temperature-range superelastic alloys and providing insights into phase-structure transformations and microstructural evolution in additively manufactured high-entropy superelastic alloys.