Effect of plasma-electrolytic oxidation on mechanical properties of titanium coatings

Abstract

The process of plasma electrolytic oxidation (PEO) allows to obtain multifunctional coatings with unique properties, including wear-resistant, corrosion-resistant, heat-resistant, electrical insulating and decorative. Therefore, the field of application of these coatings is quite wide: medicine, aircraft construction, shipbuilding, instrumentation, automotive and other industries. The technology is based on the phenomenon of micro-arc discharges promoting the formation of oxide layers on metal surfaces. In this review the technologies of obtaining coatings by plasma electrolytic oxidation on titanium are considered. The experiment on PEO of VT1-0 titanium substrate under anodic treatment with the addition of TiO₂ nanoparticles to the electrolyte was carried out. Dense, uniform oxide coatings that do not require additional surface grinding were obtained. The coating thickness values were 18.5-62.4 μm. The influence of PEO on the microhardness of calcium-phosphate coatings formed as a result of this treatment was studied. With a satisfactory thickness of the formed layer (62.4 μm), the surface microhardness value (4.04 GPa) was found to be the highest among all the treatment modes compared, simultaneously with a high elastic modulus value (348 GPa) and a small value of the indenter penetration depth on the coating (968.99 nm). These coatings were formed in an electrolyte containing calcium phosphate with the addition of 0.75g of titanium oxide nanoparticles. The increase of microhardness in comparison with the sample without coating is in 2,5 times. As a result of the carried out researches optimum modes and parameters of calcium-phosphate coatings receiving have been established and defined. It is shown that by changing the composition of the electrolyte of the micro-arc treatment process it is possible to influence significantly the structure, thickness and surface properties of the obtained coatings.