Cavitation Erosion Characteristics of HVOF Thermal Sprayed WC-cermet Coatings

Cavitation erosion (CE) and sediment erosion (SE) damage occur in the turbine runner of the hydroelectric power generation machine. Damage to these parts is a serious problem since it causes a decrease in power generation efficiency. WC cermet thermal sprayed coating is applied to the surface of these parts as the erosion resistant coating, contributing to extension of the life of the parts; however, there are few studies on the CE characteristics of the WC cermet coating. Therefore, in this study, we focused on the CE resistance of the WC cermet coating (WC-CoCr), and investigate the CE characteristics of coatings when changing the powder particle size and spraying conditions. Electrostrictive vibration type CE test was carried out, and CE volume loss were measured and compared. Furthermore, CE damaged coating surface was observed in detail by SEM. As a result, it was considered that the CE proceeded by repeating falling off of particles with the micro crack generated by the collapse pressure of the cavity as a starting point.