The effect of annealing temperature on the microstructures and mechanical properties of Ti₅₀Ni₄₇Fe₃ (at. %) shape memory alloy was investigated by using a cold-rolled alloy sheet. For this purpose, a scanning electron microscope, electron backscatter diffraction, a transmission electron microscope, X-ray diffraction, tensile tests and Vickers hardness tests were used. The evolution of the microstructures, mechanical properties and fracture morphology of Ti₅₀Ni₄₇Fe₃ alloy was studied. The results show that the recovery occurs at an annealing temperature of 500 °C, and the recrystallization occurs at 600 °C. Because of the recrystallization at 600 °C, the //RD texture disappears, and the intensity of the //RD texture decreases; the alloy reaches its maximum elongation while maintaining a high strength, and at this annealing temperature, the alloy has excellent comprehensive mechanical properties. After the temperature exceeds 600 °C, the mechanical properties of the alloy decrease sharply. With the increase of the annealing temperature, the quantity and distribution of elliptical Ti₂Ni-phase particles show almost no specific changes. Additionally, with the increase of annealing temperatures to 600 °C, the fracture surface of Ti₅₀Ni₄₇Fe₃ alloys becomes flatter.

A systematic study was conducted on the impact of annealing treatments on the microstructure and properties of cold-rolled Ti₅₀Ni₄₇Fe₃ alloys using optical microscopy, scanning electron microscopy, electron backscattered diffraction, and an electronic universal testing machine. It was found that, during low-temperature annealing (400 °C and 500 °C), the annealing time had no significant effect on the microstructure or properties of the Ti₅₀Ni₄₇Fe₃ alloy. Only elongation (δ) increased with the increase in the annealing time, and the grain orientation of the Ti₅₀Ni₄₇Fe₃ alloy was //RD (rolling direction). When annealing at medium–high temperature (600 °C), as the annealing time increased, recrystallization and grain growth processes occurred, resulting in a continuous decrease in strength and an increase in δ. Meanwhile, it was found that the grain orientation of the cold-rolled Ti₅₀Ni₄₇Fe₃ alloy changed from //RD during the recovery and recrystallization processes to //RD after the grain growth process. The orientation distribution function cross-section φ2 = 45° results indicate that the texture was mainly distributed along the γ orientation line (φ1 = 0~90°, Φ = 54.7°, φ2 = 45°). When annealed at 400 °C and 500 °C, the texture of the Ti₅₀Ni₄₇Fe₃ alloys was (111)[uvw]. When the annealing treatment was 600 °C for 120 min, a (110)[uvw] texture occurred. Additionally, ductile fracture occurred in all specimens, and the crack origin was located on one side of the fracture surface, with obvious “Y”-shaped propagation. This article studied annealing treatments of cold-rolled Ti₅₀Ni₄₇Fe₃ alloys, providing corresponding theoretical guidance for subsequent production applications.

The effect of annealing treatment on the microstructure and texture of a Ti₅₀Ni₄₇Fe₃ shape memory alloy tube was studied. The results show that the recrystallization process of a cold-rolled Ti₅₀Ni₄₇Fe₃ alloy tube occurs at 600 °C. The microstructure changes from long striped grains to equiaxed recrystallized grains. The main texture of the alloy tube is the fiber texture parallel to RD. With the increase in the annealing temperature, the crystal orientation of the alloy gradually turned to (111), and a series of secondary textures were distributed along the γ orientation line when the alloy was annealed at a lower temperature (450~600 °C). When the alloy was annealed at 650 °C, the growth of recrystallized grains made the grain orientation change, which led to the weakening of the γ-fiber texture and the formation of recrystallization textures.

The reverse transformation temperature, recovery strain and pull-out force of TiNiFe alloy pipe couplings under different diameter expansion ratios (7%, 9%, 11%, 13%, 15%) were studied. The results show that the martensite reorientation occurs and the elastic strain energy released decreases with the increase of the expansion ratio, which leads to the increase of martensite reverse transformation temperature as’ and Af’. The recovery strain increases and the recovery rate decreases with the increase of expansion ratio. The expansion ratio of pipe couplings has a great influence on the pull-out force, which is related to the fit clearance and the diameter of the connected rod. When the fit clearance is the same, the larger the expansion ratio is, the greater the pull-out force is, and when the diameter of the connected rod is the same, the pull-out force decreases with the increase of the expansion ratio.

Heat treatments after cold rolling for TiNiFe shape-memory alloys have been compared. After EBSD analysis and as calculated by the Avrami model and Arrhenius equation, the relationship between the heat-treatment temperature and manufacturing time of TiNiFe alloys is established. Through calculation, it can be found that TiNiFe alloys can obtain similar microstructures under the annealing processes of 823 K for 776 min, 827 K for 37 min, and 923 K for 12.5 min. And the recrystallization fractions are all around 50%. Nevertheless, the tensile properties and recovery stress of the alloys show almost similar values. And based on the feasibility of the annealing process, it is believed that annealing at 873 K for 37 min is the optimal choice to obtain a recrystallization fraction φ_R = 50%.