Production of rods and sheets from TiNiHf alloy with high-temperature shape memory effect by longitudinal rolling and rotary forging methods

Introduction. Ti-Ni based shape memory alloys (SMAs) are functional materials that find widespread practical application in engineering and medicine. Functional properties of Ti-Ni based alloys are sensitive to the chemical composition. To develop alloys with specific properties, ternary SMAs are being actively developed. For example, TiNiHf ternary alloys are characterized by a high-temperature shape memory effect. Today, there is a demand for SMAs used in the production of functional elements with a response temperature of more than 120 °C. These alloys must also have sufficient ductility to obtain deformed semi-finished products for the subsequent manufacture of heat-sensitive functional elements. Also among the current issues of developing the practical application of TiNiHf alloys is the lack of technological schemes for obtaining semi-finished products from TiNiHf SMAs. The purpose of this work is study the feasibility of conducting deformation processing of the studied TiNiHf alloys with a high-temperature shape memory effect and to identify the relationships between phase composition and mechanical characteristics and the applied processing method. In this work, the possibility of producing sheets and rods from TiNiHf alloys with 5 and 10 at.% Hf and 50.0 at.% Ni by longitudinal rolling, caliber rolling, and rotary forging was investigated. The research methods were: X-ray analysis, differential scanning calorimetry, and measurement of Vickers hardness. Results and discussion. It was found that the TiNiHf alloy with 10 at.% Hf has insufficient ductility. From the alloy with 5 at.% Hf, blanks in the form of sheets and rods of various sizes were obtained by using longitudinal rolling and rotary forging processes. It was shown that hot deformation allows increasing the hardness of the studied TiNiHf alloy with 5 at.% Hf compared to the cast state, from 232 HV to 242–264 HV. Cold deformation leads to a significant increase in hardness values up to 362–394 HV. Characteristic temperatures of the forward and reverse martensitic transformation are quite stable. The obtained results indicate the potential of using longitudinal rolling and rotary forging to obtain semi-finished products of TiNiHf alloys with 5 at.% Hf and to improve the functional and mechanical properties of the alloy after smelting.