Properties of a 49Ni–36Ti–15Hf High-Temperature Shape Memory Alloy in the As-Cast State

Abstract

The properties of a 49Ni–36Ti–15Hf (at %) high-temperature shape memory alloy (HTSMA) are studied comprehensively. Data on the elemental and phase compositions, the phase transformation temperatures, and the mechanical characteristics are obtained. The studies are carried out on samples cut from alloy ingots. The temperature range of the phase transformation of the alloy determined by differential thermal analysis is from M_f = 186.8°C to A_f = 275.2°C in the as-delivered state and from M_f = 188.1°C to A_f = 276.5°C after vacuum annealing. These values are suitable for designing of the required safety device. However, as-cast 49Ni–36Ti–15Hf (at %) alloy specimens undergo brittle fracture at stresses from 461 MPa (as-delivered state) to 514 MPa (after vacuum annealing at 700°C). In this connection, it is impossible to deform such samples in the afterelastic state, and the shape memory effect and the degree of shape recovery are zero in them; i.e., the as-cast 49Ni–36Ti–15Hf (at %) alloy is not suitable for designing an efficient safety device. To improve the thermomechanical characteristics, it is planned to change the HTSMA elemental composition, the conditions of deformation treatment (forging, rolling) or heat treatment of the as-cast alloy, or the deformation conditions of articles. The authors will take into account these results of studying the as-cast 49Ni–36Ti–15Hf (at %) alloy when designing various devices for nuclear power engineering.