Temperature-deformation conditions and industrial testing of NiTiNOL alloy drawing

This article presents the investigation of drawing parameters of wire products made of NiTiNOL alloy, followed by the pilot scale testing of the developed technology. The method of calculation of drawing parameters is based on experimental hardening curves of NiTiNOL alloy, presented in the form of graphs and formulas depending on the deformation temperature. Using the safety factor of the front end of the wire, the design routes for drawing the wire from a diameter of 7.0 to 0.12 mm were analyzed within the studied range of deformation temperatures. It is shown that the most rational for guaranteed fulfilment of non-breakage conditions during drawing of NiTiNOL alloy is a wire gauge of 7.0–4.0 mm at a deformation temperature of 650 °C. The experimental industrial drawing was carried out on a 7.0 mm diameter bar produced under industrial conditions using the hot pressing → hot rolling → machining technology. The hot drawing process was tested on a specially designed stand consisting of an induction heating unit, a stand with a four-roll cassette and a drawing drum, as well as a cutting machine, and an electric contact heating device to prepare the front end of the wire for drawing. The wire was drawn to a diameter of 4.0 mm under different temperature deformation conditions. On the basis of the obtained results, the dependence of the inductor power on the reduction of the cross-sectional area of the deformable wire from NiTiNOL alloy was determined. Technological directions for improving the technology were identified.