Mechanical Property Enhancement of Ti-6Al-4V by Multilayer Thin Solid Film Ti/TiO₂ Nanotubular Array Coating for Biomedical Application

With the intention of improving the mechanical properties of Ti-6Al-4V, samples were first coated with pure titanium using the physical vapor deposition (PVD) magnetron sputtering technique. The Taguchi optimization method was used to attain a higher coating on substrate adhesion. Second, pure titanium-coated samples with higher adhesion were anodized to generate TiO₂ nanotubes. Next, the TiO₂-coated specimens were heat treated at annealing temperatures of 753.15 K and 923.15 K (480 °C and 650 °C). The XRD results indicate that the varying heat treatment temperatures produced different phases, namely, anatase [753.15 K (480 °C)] and rutile [923.15 K (650 °C)]. Finally, the coated samples’ mechanical properties (surface hardness, adhesion, and fretting fatigue life) were investigated. The fretting fatigue lives of TiO₂-coated specimens at 753.15 K and 923.15 K (480 °C and 650 °C) annealing temperatures were significantly enhanced compared to uncoated samples at low and high cyclic fatigue. The results also indicate that TiO₂-coated samples heat treated at an annealing temperature of 753.15 K (480 °C) (anatase phase) are more suitable for increasing fretting fatigue life at high cyclic fatigue (HCF), while at low cyclic fatigue, the annealing temperature of 923.15 K (650 °C) seemed to be more appropriate. The fretting fatigue life enhancement of thin-film TiO₂ nanotubular array-coated Ti-6Al-4V is due to the ceramic nature of TiO₂ which produces a hard surface as well as a lower coefficient of friction of the TiO₂ nanotube surface that decreases the fretting between contacting components, namely, the sample and friction pad surfaces.