Effect of heterogeneous precipitation caused by segregation of substitutional and interstitial elements on mechanical properties of a β-type Ti alloy

This study investigates the effect of heterogeneous precipitation induced by the segregation of substitutional and interstitial elements in Ti–29Nb–13Ta–4.6Zr alloy (TNTZ) on its mechanical properties. For this, samples both with and without segregation of substitutional elements were prepared, with only the latter being subjected to long-term homogenization. It was found that micro-scale segregation of substitutional elements such as Nb, Ta, and Zr does not significantly affect mechanical properties such as fatigue strength, not even if heterogeneous precipitation occurs as a result of this segregation. On the other hand, segregation of interstitial elements was achieved by controlling the aging time. The segregation of interstitial elements creates precipitate-free zones (PFZs), grain boundary (GB) plates, and Widmanstätten α phases with migrating O atoms that all significantly affect the mechanical properties. Specifically, the PFZs have the potential to improve fatigue life, while the Widmanstätten α phase increases the tensile strength and reduces the fatigue ratio, the GB-plates reduce elongation, These results indicate that the formation of a Widmanstätten α phase by the migration of interstitial elements has a varying influence on the tensile and fatigue properties.