Influence of cooling kinetics on surface texture, hydrophilicity and scratch resistance of the oxide layers produced by thermal oxidation on Ti-6Al-4V

The properties like high strength to weight ratio and superior corrosion resistance made Ti-6Al-4V as one on the most sorted alloy among titanium alloys for the manufacturing of orthopedic and other implants. Despite these characteristics, it is accompanied by disadvantages like lower wear resistance, release of metal ions due to degradation of passive oxide layer present on the alloys causing allergic reaction to patients. This limits their application to non-articulating joints and long-term stability of the simplant is uncertain. Surface modification through different techniques is considered as viable solution to overcome the above limitations. Surface modification in the present study is carried out using thermal oxidation technique. Titanium dioxide (TiO2) layers were synthesized over the surface of Ti-6Al-4V substrate using thermal oxidation technique. The polished Ti-6Al-4V substrates were subjected to oxidation for 24 h at a temperature of 650 °C in a muffle furnace. The specimens are then brought to room temperature using furnace cooling, air cooling and oil cooling. The resultant oxide layers were characterized for surface morphology, oxide layer thickness, crystalline phase, chemical composition, wettability, surface texture, hardness, and adhesion strength. The sample subjected to oil cooling had least Sa of 0.107 μm and highest contact angle of 118.64 ± 2.53° leading to hydrophobicity. The furnace and air-cooled samples had similar Sa of 0.135 μm and 0.134 μm leading to contact angles of 78.28 ± 1.56° and 84.11 ± 1.51° which are hydrophilic in nature. The surface of the oil-cooled samples is dominated by TiO2 when compared to other oxides. The adhesion strength of the oxide layers developed was investigated by using single point progressive scratch test. The influence of surface texture, chemical nature on hydrophilicity and adhesion strength were examined. •Cooling kinetics showed a significant effect on the chemical and physical nature of oxide layers formed•Rapid cooling inhibited formation of Al2O3 on the surface by restricting the diffusion of Al to the surface•The absence of nodular Al2O3 influenced the surface texture leading to variation in hydrophilicity if the oxide layers•Surface texture had significant role on hydrophilic nature and surface damage caused during scratch testing of oxide layers