OBRABOTKAMETALLOV technology Vol. 27 No. 3 2025 functional behavior and obtain materials with special properties, the use of ternary titanium nickelide alloys containing Cu, Fe, Co, Nb, and Hf is being actively developed [8-11]. Among these alloys for high-temperature applications, alloys of the TiNiHf system should be highlighted [12–14]. Most scientific research in this field focuses on alloys with 20 at.% Hf and 50.3 at.% Ni, which provide a temperature range of shape recovery (TRSR) of 200–350 °C [15–19]. The high Hf (20 at.%) and Ni (over 50 at.%) content is attributed to observations from previous studies, which suggest that TiNiHf alloys become brittle and difficult to deform when the combined concentration of Ti and Hf exceeds 49.8 at.%. Embrittlement is attributed to the precipitation of a significant amount of an embrittling (Ti, Hf)2Ni-type phase [20]. To mitigate this, the nickel concentration is typically increased. However, if other elemental contents remain unchanged, the martensitic transformation temperature range will decrease accordingly. Therefore, a higher Hf concentration is required to achieve a high-temperature shape memory effect in these alloys. However, high Hf content significantly increases the cost, hindering their practical application. Moreover, the application of TiNiHf SMAs is also challenged by the limited control over martensitic transformation temperatures. Several industries currently require shape-memory alloys with a TRSR ranging from 120 to 200 °C, coupled with sufficient technological plasticity for the production of thermosensitive components. In addition, a significant challenge in expanding the practical applications of TiNiHf alloys lies in developing the technology for manufacturing semi-finished products of various grades, a task inextricably linked to the advancement of novel thermomechanical processing methods [21]. Earlier studies showed that rods with high mechanical properties and a shape recovery temperature of 155 °C after 2% bending could be obtained from the Ti49.0Ni49.5Hf1.5 alloy using rotary forging [22]. Reference [23] also demonstrated that a pulsed electric current could improve the technological plasticity of the Ti47.4Ni47.6Hf5.0 alloy during cold rolling. Based on the preceding discussion, and as part of our effort to develop methods for creating semifinished TiNiHf SMA products with lower Hf and Ni content, the first purpose of this study is to explore the application of thermomechanical treatments to TiNiHf alloys with 5 and 10 at.% Hf and 50 at.% Ni, using different deformation methods. The second purpose is to determine how the phase composition and mechanical characteristics of TiNiHf alloys change depending on the deformation method used. This paper investigates the production of semi-finished sheets and rods using longitudinal rolling, caliber rolling, and rotary forging. The alloy’s structure and mechanical properties were also analyzed using X-ray analysis, differential scanning calorimetry, and Vickers hardness testing. A significant result is the successful production of Ti45.0Ni50.0Hf5.0 alloy semi-finished products, including sheets (2.2 and 1.0 mm thick), a rectangular bars (6.9 × 8.5 mm), and a 5.1 mm diameter rods, all demonstrating high hardness and stable phase composition. Methods The study used two alloys with compositions Ti45.0Ni50.0Hf5.0 and Ti40.0Ni50.0Hf10.0. The starting materials were 99.99% pure iodide titanium, 99.99% pure nickel (H0 grade), and 2.5 mm diameter hafnium wire (GFI-1 grade). TiNiHf ingots containing 5 and 10 at.% Hf were produced by vacuum electric arc melting, with eight remelting cycles, and cast into a water-cooled copper mold. Hot deformation was performed by longitudinal flat and bar rolling on a DUO 300 two-roll rolling mill and by rotary forging at 850 °C. The bar rolling used a square-to-square pass schedule, with the square side changing as follows: 19→17→15→13→11→9→8→7→6 mm. Cold rolling was then performed on a QUARTO110/300 fourroll rolling mill. The martensitic transformation temperature range (TRMT) in the as-cast alloy was studied by differential scanning calorimetry (DSC) using a Mettler Toledo DSC 3+ calorimeter with a heating and cooling rate of 10 °C/min from 0 to 200 °C. The martensitic transformation temperature range (TRMT) was measured using differential scanning calorimetry (DSC) on a Mettler Toledo DSC 3+ calorimeter, with a heating/cooling rate of 10 °C/min from 0 to 200 °C. The phase composition was analyzed by X-ray diffraction analysis (XRD) using a DRON-3
RkJQdWJsaXNoZXIy MTk0ODM1