Improving Bioactivity and Corrosion Resistance of Laser-Powder-Bed-Fused Ti6Al4V with Hydroxyapatite and Titanium Oxide Nanocomposite Coatings Applied by Electrophoretic Deposition

Abstract

Hydroxyapatite (HA) coatings are commonly used on titanium alloy substrates for orthopedic and dental implants because of their excellent osteoconductivity and biocompatibility. The disparity in the coefficient of thermal expansion (CTE) between the coating and substrate can result in the formation of cracks in the HA coatings during the coating process. This study examined the effect of titania (TiO2) nanoparticle additions in HA coatings to enhance their properties and prevent cracking. Using electrophoretic deposition (EPD), HA and HA-TiO2 composite coatings were applied to laser-powder-bed-fused Ti6Al4V substrates. Optimal EPD conditions of 45 volts and 120 s were identified to produce consistent, crack-free coatings. The microstructural analysis confirmed the uniform distribution of HA and TiO2 in the coatings. X-ray diffraction and Fourier transform infrared spectroscopy data revealed that the HA structure remained intact even with the addition of TiO2. Based on the corrosion analysis, higher TiO2 content reduced the average surface roughness, with the HA-40%TiO2 coating exhibiting the lowest roughness (approximately 50 nm) while increasing the TiO2 nanoparticle concentration (>= 50 wt.%) decreased the coatings' CTE, mitigating cooling-induced cracking. Higher TiO2 reduced the average surface roughness, with the HA-40%TiO2 coating exhibiting the lowest roughness (approximately 50 nm). Electrochemical tests corroborated the surface roughness findings. Incorporating TiO2 into the HA coatings decreased the thermal expansion coefficient, reducing tensile stresses.