Mechanical behaviour of low-, medium- and high-entropy Ti-Hf-Zr-Ni-Cu-Co shape memory alloys

• Published in: Journal of alloys and compounds 2025-01, Vol.1010, p.177479, Article 177479
• Main Authors: Resnina, N., Belyaev, S., Ivanov, A., Bikbaev, R., Ponikarova, I., Starodubova, M., Rebrov, T., Bazlov, A., Andreev, V., Kalganov, V.
• Format: Article
• Language: English
• Subjects: Deformation mechanisms; High-entropy shape memory alloys; Mechanical behaviour; NiTi-based alloys; Shape memory alloys
• ISSN: 0925-8388
• DOI: 10.1016/j.jallcom.2024.177479

The mechanical behaviour was studied in twelve senary Ti-HfXZrX-Ni-CuXCoX alloys with various configuration entropies, which were regulated by the X value - concentration of doping elements (Hf, Zr, Cu, and Co) that varied from 1 at% to 17 at% and the concentration of the Ni group (Ni+Cu+Co) that varied from 49 to 51 at%. The stress vs strain curves were obtained at three temperatures (-100 °C, 22 °C and 100 °C) at which the alloys were in different states (martensite, austenite, or a mixture of both). It was found that the senary Ti-Hf-Zr-Ni-Cu-Co alloys could undergo deformation via martensite reorientation, stress-induced martensitic transformation, and dislocation slip. The activation of the mechanisms depends on the deformation temperature compared to the temperatures of the martensitic transformations, as in the binary NiTi alloys. An increase in the X value from 1 to 10 at% increased the yield limit for dislocation slip in the austenite phase, while a further rise in the X value by 17 at% decreased this limit. An increase in the X value decreased the strain up to failure. The larger the [Ni] concentration or deformation temperature, the more pronounced the reduction in strain up to failure. An increase in X value from 1 to 5 at% significantly changed the fracture mechanisms from ductile to brittle due to the suppression of the dislocation movement. •Senary Ti-Hf-Zr-Ni-Cu-Co alloys demonstrated mechanical response close to NiTi alloy.•If ΔSmix increased from 0.89 R to 1.64 R, the dislocation yield limit increased.•If ΔSmix increased from 1.64 R to 1.79 R, the dislocation yield limit decreased.•An increase in ΔSmix from 0.89 R to 1.33 R dramatically reduced strain up to failure.•The deviation of the Ni- group from 50.0 at% decreased the strain up to failure.