OBRABOTKAMETALLOV technology Vol. 27 No. 3 2025 Ta b l e 2 Martensitic transformation temperatures of processed TiNiHf SMA (Ingot 2) Sample Direct transformation Reverse transformation Ms, °С Mf, °С Mp, °С As, °С Af, °С Ap, °С Initial 74 50 21 62 92 124 HR 54 40 17 61 85 105 HRF 65 50 31 71 97 115 HBR 62 47 27 70 97 113 CR 54 36 17 52 85 107 The results showthat neither hot nor colddeformation significantly changes themartensitic transformation temperatures; they remain relatively stable with fluctuations under 10 °C. However, there’s a trend of decreasing forward MT (Af) temperature compared to the as-cast state of ingot 2. Even so, this temperature stays above 105 °C in all cases, indicating that the TiNiHf alloy maintains its high-temperature shape memory behavior. Conclusion A comprehensive investigation was undertaken to assess the feasibility of producing a range of semifinished products from TiNiHf shape memory alloys containing 5 and 10 at.% Hf with reduced Ni content, utilizing various deformation methods. Based on the findings of this study, the following conclusions can be drawn: The TiNiHf SMA with 10 at.% Hf lacks sufficient technological plasticity for thermomechanical treatment by the considered deformation methods. The TiNiHf SMA with 5 at.% Hf has sufficient technological plasticity Various deformation methods were applied to the alloy (hot and cold longitudinal rolling, bar rolling, rotary forging). High-quality semifinished products in the form of sheets and rods of various sizes were obtained. Hot deformation increases hardness from 232 HV (as-cast) to 242 HV (HR/HRF) and 264 HV (HBR). Cold deformation significantly increases hardness, reaching 362 HV (1 mm thick sheet) and 394 HV (rolling to critical strain). The characteristic temperatures of the forward and reverse martensitic transformations in the TiNiHf SMA with 5 at.% Hf remain stable after deformation. Deformation slightly decreases the finishing temperature of the reverse martensitic transformation (Af) (to 19 °C) compared to the as-cast ingot. However, Af remains above 105 °C, confirming their high-temperature shape memory behavior. Thermomechanical processing using hot and cold rolling and rotary forging is a promising method for producing TiNiHf SMA semi-finished products with 5 at.% Hf and improving the alloy’s functional and mechanical properties after melting. References 1. Sadashiva M., Sheikh M.Y., Khan N., Kurbet R., Gowda T.D. A review on application of shape memory alloys. International Journal of Recent Technology and Engineering (IJRTE), 2021, vol. 9 (6), pp. 111–120. DOI: 10.35940/ ijrte.F5438.039621. 2. Nair V.S., Nachimuthu R. The role of NiTi shape memory alloys in quality of life improvement through medical advancements: A comprehensive review. Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 2022, vol. 236 (7), pp. 923–950. DOI: 10.1177/09544119221093460. 3. Kim M.S., Heo J.K., Rodrigue H., Lee H.T., Pané S., Han M.W., Ahn S.H. Shape memory alloy (SMA) actuators: The role of material, form, and scaling effects. Advanced Materials, 2023, vol. 35 (33), p. 2208517. DOI: 10.1002/adma.202208517.
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