Electrodeposition Coatings by Ionic Co- discharge Technique

Abstract

Electrochemical co-deposition of metal with a second phase material has been widely applied in industry to improve the properties of composite coatings. Traditional composite coatings were generally prepared by suspending the second phase particles in a plating bath solution with vigorous agitation to achieve good dispersion of particles. Most research has focused on the co-deposition of metal matrix with hard oxides, carbides, nitrides, diamond, etc. However, little research has investigated the two insoluble metals coatings. The overall aim of this thesis is to study and develop two insoluble metals (or two phases) coatings using ionic co-discharge method. Bi was co-deposited with different coating metal matrices (Ni, Ag, Zn and Cu). A number of plating parameters including current density, deposition time, direct or pulse current supply and concentration of Bi ions in the electrolyte have been investigated to evaluate their effect on the coating preparation and quality. Experimental results indicated that the microstructure and properties of Bi doped coatings can be very varied on different metal matrices even the co-deposition processes were similar. In-situ formation of NiBi intermetallic compound was observed when Bi is co-deposited with Ni using the ionic codischarge process. Ag-Bi alloy was produced with Bi acting as the alloying element in Ag-Bi coating. Bi is insoluble in the Zn or Cu matrix at a relatively small proportion of Bi content. The mechanical properties of the co-deposited coatings were generally enhanced by the refined microstructure and dispersion strengthening effect due to the incorporation of Bi. The content of Bi in the coating matrix, except for Cu-Bi, was dependent on the plating parameters, which was increased with the applied current density, the employment of pulse current and the higher content of Bi in the electrolyte. All coatings developed in this work presented better mechanical properties with the incorporation of a small quantity of Bi without losing other desired properties such as corrosion resistance, conductivity and antimicrobial properties.