National University of Science and Technology MISIS (Moscow, Russia)

К. А. Polyakova, Senior Researcher of the Laboratory of Shape Memory Alloys, Candidate of Technical Sciences, vachiyan@yandex.ru
К. Е. Lukashevich, Junior Researcher of the Laboratory of Shape Memory Alloys, Candidate of Technical Sciences
V. Cherniy, Student

Institute of Metallurgy and Materials Science, RAS (Moscow, Russia)
V. А. Andreev, Leading Researcher at the Laboratory of Plastic Deformation of Metallic Materials (No. 15), Candidate of Technical Sciences

The effect of the size factor on the functional and mechanical properties of hot-drawn Ti–50.8 at.% Ni alloy wire with diameters of 0.6 and 1.2 mm was investigated. The wire diameter was found to have virtually no effect on the sequence or transformation temperatures of the martensitic transformations. However, it significantly influenced the fine substructure, with the smallerdiameter wire exhibiting a higher density of lattice defects. Static tensile tests showed that the 0.6 mm wire possessed superior strength, with an ultimate tensile strength of 1104 MPa and an elongation to failure of 22%, whereas the 1.2 mm wire exhibited an ultimate tensile strength of 999 MPa and an elongation of 41%. Cyclic tensile tests performed under a loading scheme of 5% strain followed by unloading demonstrated that the 1.2 mm wire exhibited more stable superelastic behavior with lower accumulation of residual strain. In both cases, the phase yield stress decreased monotonically during cyclic loading; however, its values remained higher for the 0.6 mm wire, decreasing from 500 to 310 MPa, compared with a decrease from 370 to 270 MPa for the 1.2 mm wire. Functional fatigue tests revealed that the 0.6 mm wire withstood more than 3,600 cycles at a constant maximum strain of 3%, whereas the 1.2 mm wire endured up to 2,500 cycles. No significant difference in the total recoverable strain was observed between the investigated wire diameters. Nevertheless, the higher initial defect density of the finer wire provided enhanced resistance to fatigue failure.
The research was carried out at the expense of the grant of the Russian Science Foundation No. 24-79-10322, available at: https://rscf.ru/project/24-79-10322/.

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