OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 3 2022 metallic materials deformability can be equal from a tenth to tens of percent, limiting or expanding the possibility of application of metal forming processes. The deformability of metallic materials before forming processes is commonly increased by application of thermal treatment (heating). However, in some cases heating is unacceptable due to accompanied changes in other properties (corrosion resistance, hydrogen embrittlement, etc.) or a decrease in economic effi ciency. Deformation processes with the use of a pulsed electric current allows solving these problems for a number of brittle or hard-to-deform metals, steels and alloys based on Ti, Zr, Al, Mg, Fe [1-15]. Among the studied materials, a special role belongs to alloys based on the TiNi ordered intermetallic compound, which performs a shape memory (SME) and superelasticity effects at temperatures close to room temperature [16, 17]. Previous studies have revealed the prospect of forming process with a pulsed current for production of thin long-length semi-fi nished products from binary Ti-Ni shape memory alloys (SMA) [2, 3, 9]. Ti-Ni SMA are actively used in various sectors of the economy due to its unique properties. The fi nishing temperature of the reverse martensitic transformation in titanium nickelide of equiatomic composition is about 80-90 °C, which put bounds to its use at higher temperatures. Recently, high-temperature multicomponent alloys with a noticeably higher temperature of martensitic transformation, in which some of the nickel or titanium atoms are replaced by hafnium atoms, was also studied [18-24]. As compared to titanium nickelide, hafnium-doped alloys are not only diffi cult to deform, but rather brittle. The need for the practical use of these alloys in the form of long thin-section products imposes increased requirements on its deformability during rolling or drawing, especially at the fi nal stages of manufacturing. Until now, there has been no information in the literature on the application of the electrostimulated forming process to TiNi-based ternary alloys with the addition of hafnium. Therefore, the development of any technologies, including electroplastic rolling, to increase the deformability of these alloys is relevant. The purpose of the paper is to study the deformability and the possibility of application of pulsed current during cold rolling of the TiNiHf alloy. This treatment has shown its effi ciency for titanium nickelide [3], however, it has not been previously applied to brittle hafnium-doped alloys, where the embrittling phase plays a signifi cant role. Materials and research methods In the present study the TiNiHf alloy, obtained in the industrial center MATEK-SMA by the method of electron beam melting from charge materials: TiNi near stoichiometric alloy in the form of a rod with a diameter of 12 mm and a hafnium wire with a diameter of 1 mm, was used. The chemical composition of the ingot is given in Table 1. Samples for rolling were cut from the ingot by the method of electrical discharge cutting in the form of strips with dimensions of 2.0×6.0×131 mm3. The shape and dimensions of the ingot and the sample for rolling are shown in Fig. 1. For fl at rolling, a two-roll mill with a roll diameter of 65 mm was used. The pulse current was supplied from a generator with the following parameters: current J = 500–5,000 A, pulse duration ≤ 1000 μs and frequency in the range ν = 1–1000 Hz. The scheme of current supply and the direction of deformation is shown in Fig. 2. The rolling rate and thickness reduction were 60 mm/s and 25 μm, respectively. The process was carried out at room temperature. To avoid overheating, the samples were cooled in water after each rolling pass. The uniform distribution of deformation along the length and thickness was ensured by rotating the sample around the longitudinal axis by 180° and changing the direction of rolling to the opposite. Ta b l e 1 Chemical composition of the alloy mass.% at.% Ti Ni Hf Ti Ni Hf 38.2 47.0 14.8 47.4 47.6 5.0
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