Improvement in fatigue strength while keeping low Youngʹs modulus of a β-type titanium alloy through yttrium oxide dispersion

Improvement in fatigue strength in spite of maintaining low Youngʹs modulus was achieved in Ti–29Nb–13Ta–4.6Zr (TNTZ) by hard-particles dispersion. A certain amount of Y2O3 additions was added into TNTZ. TNTZ with 0.05–1.00mass%Y consists of a β-phase with a small amount of Y2O3. Youngʹs moduli of TNTZ with 0.05–1.00mass%Y are maintained low, and are almost similar to that of TNTZ without Y2O3. The tensile strength of TNTZ with 0.05–1.00mass%Y is slightly improved and the elongation does not deteriorate by Y2O3 additions. However, the 0.2% proof stress decreases with the increase in Y concentration. Although tensile properties are not changed drastically, the fatigue strength is significantly improved by Y2O3 additions. The dispersion of Y2O3 particle increases the resistance to fatigue initiation. However, Y2O3 with too large diameter at the surface of the specimen works harmfully as the fatigue initiation site. The Y2O3 diameter and volume fraction increase with the increase in Y concentration. As a result, the fatigue limit of the alloys with 0.05–1.00mass%Y firstly increases and then decreases with the increase in Y concentration. TNTZ with 0.1mass% Y exhibits the best combination of higher fatigue strength and low Youngʹs modulus.