Development of tantalum oxide (ta-o) thin film coating on biomedical ti-6al-4v alloy to enhance mechanical and tribological properties, and biocompatibility / Bizhan Rahmati

Ti alloy (Ti-6Al-4V) is a one of the biomaterials that is extensively used in the human body as implants, prosthesis, dental posts, and total hip and knee joint replacements, due to its excellent mechanical properties and resistance to wear and corrosion. They are able to form efficient artificial joints via couplings of metal-on-polymer or metal-on-metal contacts. However, a high concentration of stress and direct friction between the surfaces leads to the formation of wear debris and the release of toxic metal ions into the human body, limiting its operational lifetimes. The aim of this research is to modify the surface of the Ti-6Al-4V (Ti64) alloy by creating a high adhesion thin film coating to improve its biocompatibility and decrease the release of Aluminum and Vanadium ions from corrosion and debris. Tantalum oxide (Ta-O) is proposed as a coating target material, deposited via the physical vapor deposition magnetron sputtering. Tantalum and its corresponding compounds are biocompatible materials with low ion release and high corrosion resistance. Adherent coating of multiple thicknesses, with a multilayer structure consisting of metallic tantalum and tantalum oxide, were subsequently deposited. The adhesion strength, hardness, thickness, surface roughness, wettability, wear, and corrosion and cell culture analysis of the substrate and coating were duly determined. According to the Taguchi optimization analysis, the consequence represents improvement of 6.02 %, 1.22%, 3.8%, and 10.5% in adhesion, hardness, thickness, and surface roughness, respectively, from the values obtained from 16 experiments. The sample with the highest adhesion strength is recommended for biomedical applications and is regarded as the desired sample, as it is the most durable coating. Its hardness achieved 88.5% of the highest hardness. It is also 1.4 and 2.1 times thicker and rougher (surface), respectively. Furthermore, the sample with a high adhesion strength of 2500 mN was heat treated in a box furnace at 300, 400, and 500°C. The average adhesions were recorded to be 2555,2635, and 1746 mN at 300, 400, and 500°C, respectively, while the average hardness were determined to be 558, 577, and 470 HV at 300, 400 and 500°C, respectively, and the verified surface roughness of the thermal treated coating surface at 300, 400, and 500 was 18.5, 7.96 and 10.1, respectively. The result showed that the effect of thermal treatment significantly affected adhesion at 400°C. This study also attempted to investigate corrosion and wear behaviors of fabricated Ta-O thin film coating onto Ti64. The corrosion test was carried out in fetal bovine serum (FBS). The corrosion resistance of the Ta-O film coated onto Ti64 substrate was significantly higher than the uncoated and thermal treated coating layer Ti64 substrate post-immersion of 45 min in FBS. The wear test was carried out on uncoated, coated Ti64 substrate, and treated coating layer in the presence of an FBS lubricant less than 15 N load (naturally walking load) and 1.09 m/s (simulation medium walking speed). The specific wear ratio of Ta-O coating for both untreated and thermal treated coating layer was significantly reduced to under the uncoated substrate wear ratio. Friction coefficients 0.182, 0.152, and 0.150 were realized for uncoated Ti64 substrate, Ta-O thin film coating, and thermal treated Ta-O coating at 400°C, respectively. The friction coefficients of treated and untreated Ta-O were almost equal. Therefore, it is suggested that due to noticeable corrosion and wear resistant characteristics of the Ta-O layer, Ti64 substrate needs to be replaced by untreated Ta-O coated onto a substrate specimen. Finally, Alamar Blue assay and cell culture test confirmed the acceptable levels of nontoxicity and cell growth on the surface of coated Ti64. This resulted in significant improvements to biocompatibility.