Effect of oxygen addition on microstructures and mechanical properties of Ti-7.5Mo alloy

The effect of oxygen addition on microstructures and mechanical properties of Ti-7.5Mo (wt.%) alloy has been investigated. The series of Ti-7.5Mo-xO (x = 0, 0.2, 0.3, 0.4 and 0.5 (wt.%)) alloys were solution-treated at 1173 K for 1 h followed by water quenching. Microstructure characterizations were performed by means of X-ray diffraction, scanning electron microscope, as well as transmission electron microscope. The as-quenched microstructure of each alloy was mainly composed of internally twinned α" martensite. The twinning structures in alloys with oxygen contents of zero and 0.5 wt% were both identified as {111}α"-Type I twinning. The precipitated α plates were observed in alloys with higher oxygen contents (≥0.4 wt%). This is attributed to the α-stabilizing effect by the interstitial oxygen atoms, as confirmed by the differential scanning calorimeter measurements. Based on the results of Vickers micro-hardness tests and tensile tests, the hardness, yield strength, ultimate tensile strength, and Young's modulus increased with increasing the oxygen content, while the total elongation and uniform elongation decreased. This is ascribed to the solid-solution strengthening by the addition of oxygen atoms. The present study revealed that Ti-7.5Mo alloy with oxygen content less than 0.3 wt% exhibits an excellent combination of high yield strength and elongation, as well as low Young's modulus; the alloy has good potential as biomedical materials.