Using a Procedure for Estimating Cavitation Impact for Analyzing the Erosion Resistance of Cermet Thermal Sprayed Coatings

Many machinery parts operating in contact with rapidly flowing fluid flows (for instance, turbine blades of hydroelectric power plants, valves, pump impeller blades, ship propellers, cooling systems of various assemblies, and so on) are exposed to wear such as cavitation erosion. The elimination or reduction of cavitation erosion is an urgent task, because it makes it possible to achieve significant cost efficiency. This work describes a procedure that has been developed and patented for estimating resistance against the cavitation erosion of cermet thermal sprayed coatings (WC-10Co4Cr and WC-20CrC-7Ni). The cermet coatings were produced by high velocity air fuel (HVAF) spraying. The aim of this work is to test the new estimation procedure of coating resistance against cavitation impact, which differs from the standard procedure by position of tested specimen with regard to fluid used for testing. In addition, the structure of the coatings has been analyzed in the initial state before tests and their behavior after cavitation impact has been studied using scanning electron microscopy. The coating resistance has been estimated by the criterion of material volume loss. The experimental results have demonstrated that the cavitation resistance of the WC-20CrC-7Ni coating is somewhat higher in comparison with WC-10Co4Cr, despite its lower average hardness (850 +/- 90 HV0.5 against 950 +/- 60 HV0.5). An analysis of surface and transversal cross sections of the coatings demonstrates that they are characterized by different mechanisms of erosion destruction. It can be concluded that the existence of defects (pores) in the coating structure is the main reason promoting a decrease in their resistance against cavitation erosion. Therefore, this procedure has proven its efficiency upon obtaining experimental data for an analysis of the cavitation wear of cermet thermal sprayed coatings.