Phase formations and microstructures of Ti20Zr15Hf15Ni35Cu15 high-entropy shape memory alloy under different aging conditions

The microstructures and phase formations of Ti20Zr15Hf15Ni35Cu15 high entropy shape memory alloy (HESMA) under different aging conditions were investigated in this study. At aging temperatures below 500 °C, a large amount of the H-phase formed, and the martensitic transformation temperatures were suppressed due to the strain field around the H-phase. Aging treatment at 600 °C caused a eutectoid reaction, which yielded a lamellar structure composed of (Zr,Hf)7Cu10 and Ti2Cu phases. When the aging treatment was increased to 700 °C, the lamellar structure was no longer observed, but (Zr,Hf)7Cu10 and newly-formed Ti2Ni phases formed around the original Ti2Ni phase. Experimental results demonstrated that the H-phase precipitation, eutectoid decomposition, and (Zr,Hf)7Cu10 formation occurred at different aging temperatures. These results could be utilized to adjust the martensitic transformation temperatures and design microstructures, providing a new strategy for developing TiZrHfNiCu HESMAs. © 2022 The Authors