Effect of suspension stability on bonding strength and electrochemical behavior of electrophoretically deposited HA-YSZ nanostructured composite coatings

In the present study, HA-YSZ nanostructured composites were deposited on Ti-6Al-4 V substrates by electrophoretic deposition of suspensions containing 0, 10, 20 and 40 wt% YSZ. The stability of each suspension was determined by applying response surface methodology, DLVO theory and zeta potential measurement for different YSZ contents and dispersant concentrations. The maximum zeta potential and electromobility of suspended particles was obtained for the suspension with 20 wt% YSZ. The electrophoretic deposition of HA-YSZ nanostructured composites was carried out at a constant voltage of 20 V for 120 s. The deposition kinetics was studied based on a mass-charge correlating approach under ranges of voltage (20-60 V), time (30-300 s) and wt% YSZ (0-40). The as-deposited and sintered HA-YSZ coatings were characterized by SEM, XRD, DSC-TG and FT-IR analyses. The micro-scratch behavior of coated samples indicated the highest critical contact pressures of crack initiation, Pc1 = 4.50 GPa, crack delamination, Pc2 = 5.14 GPa and fracture toughness, KIC = 0.622 MPa m1/2 for HA-20 wt% YSZ sample. The results of potentiodynamic polarization measurements showed that the implementation of 20 wt% YSZ could efficiently decrease the corrosion current density and corrosion rate of coated samples, while corrosion potential and linear polarization resistance were increased.