Microstructure and cavitation erosion behavior of HVOF sprayed ceramic-metal composite coatings for application in hydro-turbines

摘要

Cavitation erosion commonly occurs in hydro-turbine blades and has been a crucial issue for operation of hydro-turbines. In this paper, high-velocity oxygen-fuel (HVOF) spraying was applied to produce Cr3C2-NiCr and WC-CoCr ceramic-metal coatings. The microstructure and the relationship between the flow velocity and cavitation erosion behavior of the coatings were evaluated, and their cavitation erosion mechanisms at different flow velocities were discussed. Experimental results showed that the WC-CoCr coating exhibited slightly lower porosity and significantly higher microhardness as compared to the Cr3C2-NiCr coating. Both ceramic-metal coatings were combined well with the steel substrate and showed an increase in the volume loss rates with increasing flow velocity. The volume loss rates for the WC-CoCr coatings were lower than that of the Cr3C2-NiCr coatings at each flow velocity. The critical flow velocity of the Cr3C2-NiCr coating was in the region of 33.5-41.9 m s(-1). The cavitation erosion process of the Cr3C2-NiCr coatings mainly included removal of chromium carbide particles, coalescence of the craters and brittle detachment of the coating, while the failure mechanism of the WC-CoCr coatings was erosion of the binder phase at 23.4 m s(-1), cavitation pits interlinking at 33.5 m s(-1), and detachment of the WC particles at 41.9 m s(-1). (c) 2020 Elsevier Ltd. All rights reserved.