Abstract
Complex studies of the properties of Ni49,5Ti48Hf2,5 alloy featuring high-temperature shape memory effect were carried out on samples made of 2,34 mm-thick strip after high-temperature annealing in vacuum (850 ºС, 1 h). Data on element, phase compositions and structure state was obtained. Results of studies of phase transition temperatures, mechanical and thermomechanical characteristics of the alloy are given. According to the results of studying the local phase composition of alloy samples, it was found that the main matrix of samples is formed by solid solution of Ti, Ni, Hf elements. When analyzing diffraction patterns, it was found that the main phase of samples is titanium nickelide in the low-temperature martensitic state TiNi (B19`) with a monoclinically distorted orthorhombic crystal lattice. It was found that the best average values of the shape memory characteristics εSME = 4,4 % and ηSME = 53 % were obtained for alloy samples with a previously induced total deformation of eо = 11 % in the temperature range tD=(–5 ÷ 23) ºС and deformation rate ε ≈ 2,8·10–3 s–1. The average values of temperatures of the start and the end of the main form recovery are Аs SME = 133 ºС, Аf SME = 149 ºС. These thermomechanical characteristics are suitable for alloy selected to create safety devices such as devices of pushing type.
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