Nacre coatings deposited by electrophoresis on Ti6Al4V substrates

Crack-free nacre coatings on titanium alloys were produced by electrophoretic deposition in a nacre/ethanol suspension with or without a hydrochloric acid (HCl) additive. The microstructure and morphology of coatings were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The deposition yield of nacre powders was determined by weighting the dried deposits. The results show that the HCl additive has no obvious effects on the crystalline phase of nacre coatings. The deposition yield of nacre powders increases with adding acid additives, prolonging deposition time, and improving applied voltage. A uniform and glue-like nacre coating is deposited in a suspension with the HCl additive via a dissolution-precipitation reaction. After the HCl additive is added into a nacre/ethanol suspension, calcium ions are released from nacre powder surfaces, and move toward the cathode within an electric field. The local concentrations of hydroxide ions and carbonate ions increase due to the reduction of hydrogen ions at the cathode surface. Calcium ions react with carbonate ions to form calcium carbonate as the ionic activity product exceeds its thermodynamic solubility product, and re-precipitates on the active sites of nacre powder surfaces.