Structure-property relationship of cast Ti-Nb alloys

The present work is a study of the microstructure, mechanical, properties and corrosion behaviour of a series of binary Ti-Nb alloys with Nb contents up to 35 wt%, with emphasis placed on the structure-property relationship of the alloys. The results indicate that crystal structure and morphology of the Ti-Nb alloys are sensitive to the Nb content. The cast c.p. Ti has a hexagonal α phase with a lath type morphology. The alloys containing 15 wt% or less Nb are dominated by a hexagonal α′ phase with an acicular, martensitic structure. When containing 17.5-25 wt% Nb, the alloys are primarily comprised of an orthorhombic α″ phase. With 27.5 wt% Nb, metastable β phase starts to be retained. With Nb contents higher than 30 wt%, the equi-axed β phase is almost entirely retained. Small amounts of ω phase are detected in alloys containing 27.5 and 30 wt% Nb. Among all present alloys, Ti-10Nb and Ti-27.5Nb exhibit the highest strengths, while the α″-dominated (17.5 and 20Nb) and β-dominated (> 30Nb) alloys have the lowest moduli. All Ti-Nb alloys show excellent corrosion resistance in Hank's solution at 37°C. From the present data, the microhardness, bending strength and modulus of the various phases in Ti-Nb alloys are compared and tentatively summarized as follows: Microhardness: ω > α′ > α″ > β > α (c.p. Ti) Bending strength: ω > α′ > α″ > β > α (c.p. Ti) Bending modulus: ω > α (c.p. Ti) > α′ > α″ > β.