Effect of O addition on microstructure and mechanical properties of Ti-Nb alloys with various β stability.

To study the effect of O on β-Ti alloys with various β phase stability, Ti– x Nb–0.4O (x = 30, 32, 34, 36, 38, 40, 42, mass%) alloys were prepared by arc melting followed by homogenization, hot rolling, and solution treatment. To ensure the O content of the alloys, melting and hot rolling were performed under an Ar atmosphere, and homogenization and solution treatment were performed under vacuum conditions. The mass fractions of O in the Ti–Nb–O alloys were finally accurately controlled in the range of 0.4–0.5%. The phase composition of the alloys was determined by analyzing the X-ray diffraction patterns, the microstructure was observed by optical microscopy, and the mechanical properties were measured by tensile tests. The ω phase and α" phase were found in the solution-treated Ti–30Nb–0.4O. Ti–30Nb–0.4O showed the lowest yield strength owing to the existence of the α" phase. O suppressed ω phase and α" phase transformations during quenching, and showed an obvious solution-strengthening effect. Because the O content of the alloys was essentially the same, the Ti– x Nb–0.4O alloys showed similar tensile strengths. The Young's moduli of the alloys ranged from 60 to 69 GPa, and the elongations were all higher than 15%. Particularly, Ti–36Nb–0.4O exhibited desirable mechanical properties, including a Young's modulus of 61 GPa, a tensile strength of 760 MPa, and an elongation of approximately 35%. • The O content was accurately controlled in the range of 0.4–0.5% using high vacuum equipment. • O effectively suppressed the formations of the α" phase and ω phase during quenching. • Ti-36Nb 0.4O alloy exhibited desirable high strength and low Young's modulus. [ABSTRACT FROM AUTHOR]