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The properties of the Ni50Ti47.5Hf2.5 alloy with a high-temperature shape memory effect have been comprehensively studied on samples made from a 2.34-mm-thick strip in the initial state and after high-temperature annealing in vacuum. Data on the elemental and phase compositions and structural state have been obtained. The results of investigations of the phase transformation temperatures and the mechanical and thermomechanical characteristics of the alloy are reported. Using annealing and selecting the strain-inducing conditions, the shape recovery temperatures AsSME = 137°C and AfSME = 150°C have been determined. These values are acceptable for creating the required depressurization device. The maximum εSME and ηSME values have been found to be 3.4 and 43%, respectively. These are not very large values for creating an efficient depressurization device for nuclear power plants. The desired displacement values in such a device can be obtained by optimizing the geometry of a thermosensitive element. [ABSTRACT FROM AUTHOR]

The properties of an Ni49.5Ti48Hf2.5 high-temperature shape memory effect alloy are comprehensively studied on samples made of a 2.34-mm-thick strip after high-temperature vacuum annealing (850°C, 1 h). The elemental, phase compositions and structure of the alloy are analyzed. The results of studying the phase transformation temperatures and the mechanical and thermomechanical characteristics of the alloy are presented. The results of studying the local phase composition of the alloy samples demonstrate that their matrix is formed by a solid solution of alloy elements (Ti, Ni, Hf). X-ray diffraction analysis demonstrates that the main phase of the samples is titanium nickelide in the low-temperature TiNi martensitic state (B19') with a monoclinically distorted orthorhombic crystal lattice. The best average shape memory characteristics (εSME = 4.4%, ηSME = 53%) are obtained for alloy samples subjected to preliminarily induced total strain εt = 11% in the temperature Td range from –5 to 23°C at a strain rate ≈ 2.8 × 10–3 s–1. Here, the average temperatures of the onset and end of the main shape recovery are AsSME = 133°C and AfSME = 149°C. These thermomechanical characteristics are acceptable for the alloy chosen to create safety devices of, e.g., a pushing type. [ABSTRACT FROM AUTHOR]