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

Improvement in fatigue strength in spite of maintaining low Young's 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 Y ₂O₃. Young's moduli of TNTZ with 0.05-1.00mass%Y are maintained low, and are almost similar to that of TNTZ without Y ₂O₃. The tensile strength of TNTZ with 0.05-1.00mass%Y is slightly improved and the elongation does not deteriorate by Y₂O ₃ 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 Y ₂O₃ additions. The dispersion of Y₂O ₃ 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 Y₂O ₃ 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 Young's modulus.