Improvement in Fatigue Strength of Biomedical β-type Ti–Nb–Ta–Zr Alloy While Maintaining Low Young’s Modulus Through Optimizing ω-Phase Precipitation

The improvement in fatigue strength, with maintenance of a low Young’s modulus, in a biomedical β-type titanium alloy, Ti–29Nb–13Ta–4.6Zr (TNTZ), by thermomechanical treatment was investigated. A short aging time at an ω-phase-forming temperature combined with severe cold rolling was employed. A fine ω phase is observed in TNTZ subjected to this thermomechanical treatment. Because the rolling texture of β phase is formed by cold rolling, such as the ω phase may be preferentially oriented to a direction that is effective for inhibiting the increase in Young’s modulus. The samples aged at 573 K (300 °C) for 3.6 ks and 10.8 ks after cold rolling exhibit a good balance between a high tensile strength and low Young’s modulus. In the case of the sample aged for 3.6 ks, the tensile strength is improved, although the fatigue strength is not improved significantly. Both the tensile strength and the fatigue strength of the sample aged for 10.8 ks are improved. This fatigue strength is the highest among the TNTZ samples used in the current and in previous studies with Young’s moduli less than 80 GPa.