Behaviour of nickel coatings made by brush plating technology in conditions of cavitation erosion and corrosion

The basic hypothesis of the research was that the structure of the coating, i.e. the type of defects, affects the mechanical and electrochemical properties, as well as the resistance to cavitation erosion and corrosion. For this purpose, nickel coatings produced by brush-plating technology using two different electrolytes and deposited on X20Cr13 steel were tested. The electrolytes affected the structure and properties of the coatings: one coating had a network of cracks, and the second one had a "cauliflower-like" structure. The hardness and Young's modulus of both coatings were investigated under multi-cycle loading modes. Cavitation erosion resistance was tested in a cavitation tunnel equipped with a barricade system at an inlet pressure of 600 kPa and outlet pressure of 120 kPa. Both nickel coatings protected the substrate against cavitation erosion. The lowest rate of cavitation erosion had a coating with a network of cracks and high hardness. Microscopic examinations showed no influence of the net of cracks on the degradation process. Electrochemical tests confirmed the better corrosion resistance of the compact coating. The compact coating had about an order of magnitude lower corrosion potential and about 100 mV higher corrosion current density than that of the agglomerate coating. The agglomerate coating had electrochemical parameters comparable to the substrate.