Oxidation Kinetics, Phase Evolution, and Surface Characteristics of Ti-35Nb-6Mo β-Titanium Alloy at Elevated Temperatures

This present study investigates the high-temperature oxidation behavior and microstructural evolution of Ti-35Nb-6Mo β-titanium alloy at 600°C, 700°C, and 800°C for exposure durations from 0.5 to 72 hours. A comprehensive experimental approach combining gravimetric analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), focused ion beam (FIB) cross-sectional analysis, optical profilometry, and contact angle measurements was employed. The oxidation kinetics exhibited a strong temperature dependence. At 600°C, oxidation followed near-linear kinetics with low mass gain, indicating the formation of a thin and protective oxide layer. At 700°C, the kinetics transitioned to diffusion-controlled behavior, consistent with parabolic trends, associated with the development of a multilayered oxide scale comprising rutile TiO ₂ and sub-stoichiometric Ti ₃ O ₅ . At 800°C, oxidation became non-protective, showing sustained linear kinetics and significantly higher mass gain due to oxide scale cracking, porosity, and spallation. Microstructural analysis revealed progressive oxide thickening and increased crystallinity with temperature, with rutile TiO ₂ dominating at higher temperatures. Surface roughness increased markedly with oxidation severity, while contact angle measurements indicated enhanced hydrophilicity due to combined effects of oxide chemistry and surface topography. The results demonstrate that Ti-35Nb-6Mo exhibits stable oxidation resistance up to 700°C, while degradation at 800°C defines its upper thermal limit. These findings highlight the alloy’s potential for both high-temperature engineering applications and surface-engineered biomedical applications.