Due to the high deposition efficiency of WC, HVOF sprayed WC-M coating has a dense microstructure and high adhesive strength with the substrate, it also combines the high hardness of WC particles and high toughness of metal binder, which lead to excellent erosion resistance, and was used to prevent the surfaces damage of flow parts of water turbine from severe erosion by slurry with different sand concentrations, impact velocity and impact angle. So it is important and constructive for the development of new erosion resistant coating and the confirmation of its application environment to investigate the slurry erosion resistance and erosion mechanism of this composite coating used in practice.
In this paper, a slurry pot erosion equipment and a slurry jet erosion equipment were designed and developed, both of which can conveniently change the sand concentration, impact velocity and impact angle. A water cooling system was installed in the slurry pot erosion equipment to ensure the low constant temperature of experimental environment; and baffle plates were added in the slurry pot to make the experimental conditions be more close to the work environment of water turbine blade. The slurry jet erosion equipment could accurately control the experimental condition of the slurry jet impact such as sand concentration, impact velocity and impact angle.
The slurry erosion behavior of nine WC-Co-Cr coatings sprayed by three different HVOF spray systems was studied on the self-manufactured slurry pot erosion equipment, with martensitic stainless steel 0Cr13Ni5Mo, which is always used to produce flow parts of water turbine, as the parallel sample. Erodent used in this paper was 210µm-420µm angular quartz sand, with sand concentration of 20wt.%, nominal impact angle of 15°, 45°, 75°, 90°; the rotary speed of sample was 6m/s and the erosion time of 12h, 24h, 36h was chosen.The experimental results indicated that, the erosion mass loss of nine HVOF sprayed WC-Co-Cr coatings under every experimental condition was far less than 0Cr13Ni5Mo stainless steel; the amplitude of variation of the erosion mass loss of the coating with impact angle was much smaller, and the erosion mass loss of the coating, which had fine combination of WC particles and Co-Cr binder and no splat boundaries and cracks, was insensitive to impact angle. So the HVOF sprayed WC-Co-Cr coating is an ideal erosion resistant protective coating for improving the service life of flow parts of water turbine.
The erosion mechanism of HVOF sprayed WC-Co-Cr coating was analyzed by observing the surface SEM morphology of the coating after erosion. The results indicated that, the erosion mass loss of coating mostly came from detachment of splats. The extent of detachment of splats had a close relation with coating porosity, that the coating with high porosity was more severe.
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