Corrosion properties of micro- and nanocomposite copper matrix coatings produced from a copper pyrophosphate bath under pulse current

The aim of this work was the deposition of copper matrix composites under direct and pulse current at different frequencies and the evaluation of their protective properties, in the frame of the research domain of the production of metal matrix composite coatings. The deposits were produced using copper pyrophosphate bath in which 20 g/l of either micro- (mean diameter 2 μm) or nano- (mean diameter 45 nm) SiC particles have been added. A squared current waveform was used with the frequencies 0.01, 0.1, 1, and 10 Hz for the pulse current deposition. The microstructure of all deposits, both on the top surface and in cross section, was studied by Scanning Electron Microscopy. The SiC content was evaluated by EDXs in the case of the micro-composite deposits and by Glow Discharge Optical Emission Spectroscopy for the nanocomposite ones. The protective properties were examined by potentiodynamic measurements in different corrosive environments and by salt spray exposure combined with Electrochemical Impedance Spectroscopy measurements. Both the nanoparticles incorporation and the use of pulse current lead to a noticeable grain refinement and thus to a corrosion resistance increase. The nanocomposite deposits present the highest resistance to both uniform and localized corrosion, strongly correlated to their compact structure. The micro-composite deposits produced under direct current present gaps between the particles and the copper matrix, which lower the corrosion resistance. The use of the pulse current managed to partially close these gaps and increase the corrosion resistance to values similar to those of the pure copper deposits.