Attainment of Large Thermal Hysteresis and Good Cyclic Stability in Multi-Component TiHfZrNi Alloys

Abstract

Shape memory alloys (SMAs) hold great promise for phase-change-based energy storage, demanding attainment of both large thermal hysteresis and good cyclic stability. Nevertheless, these two properties are often mutually exclusive. Here we developed a multicomponent Ti33Hf15Zr5Ni47 alloy that exhibits a large hysteresis of 44.6 °C and a small transformation temperature shift of 0.5 °C after 20 thermal cycles. This performance is superior for applications of thermal management, surpassing most TiNi-based SMAs. The presence of Hf and Zr atoms with larger size increases the lattice mismatch between the austenite and martensite phases, thereby enlarging the thermal hysteresis. Simultaneously, these atoms tend to form heterogeneous lattice strains and chemical short-range order, strengthening the matrix. As a result, fewer defects accumulate during thermal cycling, leading to good cyclic stability. The multi-component high entropy SMAs provides an alternative approach to balance conflicting properties such as large thermal hysteresis and good cyclic stability.

Keywords: High entropy alloys, Lattice compatibility, Solid solution strengthening, Chemical short-range ordered structures, Shape memory alloys