Preparation and characterization of Ti5Al16O34 PEO ceramic coatings deposited on CP-Ti in mixed aluminate-phosphate electrolytes

Abstract

Oxide ceramic layers of Ti5Al16O34 were fabricated on commercially pure titanium grade 2 substrates by plasma electrolytic oxidation in aqueous electrolyte media at a fixed 10 g/L concentration of trisodium phosphate and 25 g/L sodium aluminate. Lowering the sodium aluminate concentration to 15 g/L and 20 g/L, β-TiAl2O5 and Ti2Al6O13 components were produced under similar PEO processing conditions. The composition and structure of the PEO coatings were studied using XPS, XRD, SEM, EDS, mechanical (hardness, adhesion, and tribology), electrochemical impedance spectroscopy, and potentiodynamic polarization tests. The layers possess a polycrystalline character with minor amorphous phases, while their thicknesses varied slightly between samples with similar treatment times. The PEO coatings consist of a compact inner layer with an enriched phosphorus content of about 5–10 wt% and a porous outer layer in which phosphorus is found in less than 1 wt%. Ti5Al16O34 coatings showed better mechanical performance regarding microhardness and corrosion resistance compared to β-TiAl2O5 and Ti2Al6O13. At a longer applied PEO process duration of 10 min, Ti5Al16O34 layer thickness, microhardness, and corrosion current densities of 40.2 μm, 9.37 GPa, and 2.8 nA/cm2 were measured.