Formation of microstructure and mechanical properties of Ti13Nb13Zr medical titanium alloy

The article presents the results of the microstructure and selected mechanical properties of the medical titanium alloy Ti13Nb13Zr. These results were obtained through heat treatment of the alloy, which involved cooling it in the β range (900 °C) and subsequently aging it at various temperatures (350, 450, and 550 °C). The mechanical properties of the alloy were evaluated through tests that determined its strength and plastic indices, including hardness, tensile strength, yield strength, fatigue strength, elongation, and reduction of area. Additionally, the fracture toughness was assessed using the KIc and KV tests. The results of the Charpy impact tests were supported by fractographic documentation of fractures. Furthermore, the fatigue strength test results were presented in the form of elaborated Wöhler curves for each aging temperature. The study revealed that cooling the alloy in the β range resulted in a martensitic transformation and the formation of titanium martensite (α') in the microstructure. However, within the tested range of aging temperatures (350–550 °C), a gradual change in the microstructure was observed, along with the separation of new α and β phases from the titanium martensite. As the aging temperature increased from 350 to 550 °C, the hardness, tensile strength, yield strength, and fatigue strength of the alloy also increased. However, these changes were accompanied by a decrease in plastic properties and fracture toughness (KIc, KV). Additionally, increasing the aging temperature led to a change in the fracture character of the samples, with an increase in fracture dispersion and a shift in the proportions of intercrystalline and transcrystalline fracture. Consequently, these changes resulted in a decrease in fracture toughness and an increase in the strength properties of the alloy.