Oxygen addition in biomedical Ti–Nb alloys with low Nb contents: Effect on the microstructure and mechanical properties

Abstract Ti–Nb alloys have been widely researched for biomedical applications because of their excellent mechanical properties, corrosion resistance, and superior biocompatibility. In this investigation, the influence of oxygen content on the microstructure and mechanical properties of Ti–Nb alloys with relatively low Nb contents was evaluated. Arc-melted Ti–Nb–O ingots (Nb contents were 15, 17.5, 20, and 22.5 wt% and O contents were 0.15, 0.25, and 0.40 wt%) were hot-rolled and solution-treated at 1200 °C for 1 h, followed by furnace cooling. These samples were characterized by scanning electron microscopy, differential scanning calorimetry, compression tests, and measuring hardness and Young's modulus. The furnace-cooled alloys exhibited typical α + β microstructures, in which the thickness of the α plates decreased with increasing Nb content and increased slightly with increasing oxygen content. A similar behavior was observed for the apparent β-transus, which decreased with increasing Nb content, and increased with increasing oxygen content. The obtained hardness and 0.2% compressive yield stress improved with increasing concentrations of alloying elements. This was due to the solid-solution strengthening promoted by Nb and oxygen, and microstructural refinement induced by Nb addition. The Young's modulus was found to increase very slowly with increasing oxygen content. Owing to the enhancement in yield stress and the small change in elastic modulus with increasing oxygen content, alloys can be designed and produced with high mechanical strength/Young's modulus ratios, favoring their application as biomaterials.