Fabrication of cavitation erosion resistant bronze coatings by thermal and kinetic spraying for maritime applications

The present study describes prerequisites for the application of cavitation resistant bronzes by different coating techniques, i.e. cold spraying, HVOF spraying, warm spraying and arc spraying. By optimization to cavitation resistance, these coatings can increase the service life of ship rudders significantly and even serve as repair processes for ship propellers. As guideline for process selection, optimum coating properties, as achieved by the different spray techniques, are compared to bulk shipbuilding steel and highly cavitation erosion resistant nickel aluminum bronze. The process descriptions and parameter sets in this work aim at coating flat structures with a typical coating thickness between 300 and 600 µm. The investigated spray techniques could provide cavitation resistance that meets the requirements with respect to applications on ship rudders. By using warm spraying and cold spraying, properties similar to those of cast nickel aluminum bronze were achieved, however at relatively high costs. In contrast, coatings produced by using HVOF and arc spraying have erosion rates that are only about four respectively three times higher compared to cast nickel aluminum bronze, while outperforming bulk shipbuilding steel. In summary, particularly with respect to costs, HVOF and arc spraying therefore represent a good compromise to reach acceptable coating properties.