Search

The structure and microhardness of the Ti50Pd30Ni20 (at %) alloy with a high-temperature shape memory effect have been comprehensively studied. The investigations have been carried out on the alloy samples cut from a 2.09-mm-thick strip in the initial state and after heat treatment under different conditions. Data on the elemental and phase compositions, microstructure, grain size, and microhardness have been obtained. It has been found that the main phase of the Ti50Pd30Ni20 (at %) alloy in the initial state and after heat treatment is a solid solution based on the TiPd (B19) phase in a low-temperature martensitic state with an orthorhombic crystal lattice; Ni is introduced in the TiPd (B19) phase with the formation of a solid solution with it. Heat treatment barely changes the parameters aexp, bexp, and cexp as compared with the initial state; i.e., the crystal lattice distortions caused by defects are minor, and the changes in the crystal lattice parameters a, b, and c as compared with the reference values are caused mainly by the deviation of the alloy composition from the stoichiometric one and by the formation of a solid solution based on the TiPd (B19) phase. [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]