Effect of additive for preparation of reduced-porosity ceramic layer on Ti-6Al-4 V alloy for orthopaedic and trauma implants

The micro-arc oxidation (MAO) method using a pulsed unipolar source was used to prepare coatings suitable for orthopaedic and trauma implants. The application of the MAO pilot plant containing the alkaline electrolyte Na2SiO3 center dot 9H(2)O, NaOH and glycerol additive was studied on a Ti-6Al-4 V alloy while focusing on reducing the pore size and improving the tribological and corrosion properties. The effects of stress, discharge time, duty cycle and the effect of the additive on the morphology of the coating, coating thickness, pore size, chemical and phase composition, wear resistance and corrosion resistance were described. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) methods equipped with X-ray energy dispersive spectroscopy (EDX), pin-on-disc, tribometer, potentiodynamic polarisation were used to characterise the coatings. Pulsation of the unipolar source and microdischarge intensity of voltage influenced the growth of the sample surface layer, surface morphology and silicon content in the analysed coating. A significant difference in pore sizes was confirmed when a glycerol-containing electrolyte was applied. The pore size distribution influenced the wear resistance and stability of the coefficient of friction. The corrosion behaviour of the prepared coatings on Ti6Al-4 V alloy was studied in physiological solutions and evaluated by using potentiodynamic curves. Corrosion resistance was evaluated based on the corrosion potentials, current densities, and polarisation resistance; a significant improvement in corrosion resistance was observed in the coatings prepared in the electrolyte with added glycerol and the presence of smaller pores.