Attainment of large thermal hysteresis and good thermal cyclic stability in multi-component TiHfZrNi alloys

Shape memory alloys (SMAs) hold great promise for phase-change-based energy storage, demanding attainment of both large thermal hysteresis and good thermal 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 degrees C and a small transformation temperature shift of 0.5 degrees C after 20 thermal cycles. This performance is superior for applications in thermal management, surpassing most TiNi-based SMAs. The presence of Hf and Zr atoms with a 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 thermal cyclic stability. Multicomponent high-entropy SMAs provide an alternative approach to balancing conflicting properties such as large thermal hysteresis and good thermal cyclic stability.