This paper describes the design of a low-cost α+β type Ti-4V-0.6O alloy and the investigation of its microstructure and mechanical properties, with a focus on heat treatability. The β transus (T β ) of the alloy was found to be 1195 K, as determined from the relationship between the heat treatment temperature and the volume fraction of the equiaxed α phase (f α ). The formation of α ′ martensite exhibiting an acicular morphology was observed after heat treatments between 1073 and 1273 K. The O content in the equiaxed α and β phases increased with increasing heat treatment temperature while the V content increased with decreasing heat treatment temperature. The alloy demonstrated a higher tensile strength and lower total elongation when heat-treated between 1073 and 1173 K as compared to the as-forged material, because of the formation of α ′ martensite. The reduced total elongation was caused by the increase in the hardness difference between the equiaxed α and β (α ′ martensite) grains. The tensile strength and total elongation of the Ti-4V-0.6O alloy were comparable to those of the Ti-6Al-4V alloy, which marks the material as a low-cost α+β type Ti alloy candidate. [

Ti-(5–20)Nb-(0.5–1)O alloys (mass%) were investigated for developing low-cost biomedical α+β-type Ti alloy. Ti-(5, 10, 15, 20)Nb-(0.5, 0.75, 1)O alloys (mass%) were arc-melted and forged into bars. The forged alloy bars were heat-treated at 873 to 1373 K for 3.6 ks in an Ar atmosphere and quenched in iced water. β transus (Tβ) of the Ti-Nb-O alloys decreased with increasing Nb content. An increase in the oxygen content led to an increase in Tβ. After quenching, the formation of α′ martensite was observed in Ti-5Nb-yO alloys. An increase in the Nb content to 10 mass% led to the formation of α′ and α″ martensites. A further increase in the Nb content to 15 and 20mass% resulted in the formation of more α″ martensites. The boundary temperature for the formation of α′ and α″ martensite in the Ti-10Nb-yO alloys increased with increasing oxygen content, because oxygen enhances the Nb distribution to the β phase. The ultimate tensile strength of the Ti-xNb-0.75O alloys heattreated to obtain the α-phase fraction (fα) of 0.5 was over 1000 MPa, except for the Ti-15Nb-0.75O alloy. The total elongation decreased with increasing Nb content. The Ti-5Nb-0.75O alloy exhibited excellent strength-ductility balance as a low-cost α+β-type biomedical Ti alloy.

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