Influence of rotary forging and post-deformation annealing on mechanical and functional properties of titanium nickelide.

This work studies the influence of thermomechanical processing modes, including rotary forging and post-deformation annealing at various temperatures and holding times, on the structure and mechanical properties of titanium nickelide alloy with shape memory effect of near-equiatomic composition. Rotary forging was carried out at a temperature of 450 °C from 12 to 5 mm with a true accumulated strain of e = 1.8. Post-deformation annealing was carried out in the temperature range from 450 to 550 °C for 0.5–1 h. The structure of the alloy following rotary forging and post-deformation annealing was studied using transmission electron microscopy. Mechanical properties were studied by tensile testing. Functional properties were determined using the thermomechanical method under bending deformation. It was found that rotary forging leads to the formation of an ultrafine-grained structure in the TiNi alloy with a high density of defects and sizes of structural elements in the range of 100–250 nm. Post-deformation annealing at 450 °C results in no increase in the average size of structural elements. At the same time, the dislocation density visually decreases. After rotary forging, the TiNi SMA rod is characterized by strong strain hardening compared to the state after reference treatment (annealing at 750 °C, 30 min, cooling in water), since a sharp increase in strength characteristics is observed. Post-deformation annealing leads to a slight decrease in strain hardening, and with an increase in the post-deformation annealing temperature and holding time, a more noticeable decrease in strength characteristics occurs. After inducing 7% strain, there is no residual strain following all considered rotary forging and post-deformation annealing regimes, with the exception of annealing at a temperature of 550 °C for 1 h, which is a confirmation of a significant increase in the shape recovery characteristics as a result of the applied processing modes. [ABSTRACT FROM AUTHOR]