Study On Preparation And Cavitation Erosion Resistance Performance Of High Velocity Oxygen Fuel Sprayed Nanostructured WC-12Co Coatings

Hydraulic turbine is the device which turns kinetic energy of water into circumrotation power energy, and make dynamotor working, then transfer energy to other place. Cavitation erosion and wear are the major problems of hydraulic turbines and other hydro-equipments, which may causes hydraulic turbines to reduce power and then to stop working. With the attention to energy by worldwide people, researches on cavitation erosion have been noticed widely in the world.On the basis of summarizing publications on cavitation erosion damage of hydraulic turbine, nanomaterials and interrelated area, depending on the failure mechanisms and excellent performance of nanomaterials, nanostructured WC-12Co coatings were deposited by HVOF, and the coatings' properties were studied by some tests. Anti-cavitation erosion performance of nanostructured coatings was expected more excellent than the conventional one because of their higher hardness and stronger toughness.The microstructure and morphology were studied by Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD). The results showed that coatings deposited by HVOF all possess a low factor of porosity and dense structure, and obvious lamellar structure can't be observed in coatings. WC particle in nanostructured coatings distribute more uniformly than in the conventional coating. Coatings are composed of WC, Co and few W₂C structure by XRD analysis and it can be demonstrated that the oxidation in spraying process has been controlled by correct parameteres of HVOF.The properties of adhesion, hardness and abrasive erosion resistance of coatings were investigated. Microstructure of coatings and surface morphology of coatings were analyzed by SEM. The results showed that nanostructured coatings exhibit more excellent performance in adhesion for enough deformed nanostructured particle. The nanostructured WC-12Co coating showed better properties not only in density and hardness, but also in distributing of WC and resistance of abrasive erosion than the conventional. And its micohardness results reach to HV1610 and is1.5 times to the conventional one. Erosion abrasive rate of the nanostructures coatings reduce 50% in comparison with the conventional. Plastic deformation in nanostructured coatings can be observed obviously by SEM and WC particles will flake away from the coating without apparent plastic deformation in the conventional coating.Anti cavitation erosion properties were studied by ultrasonic vibration cavitation equipment. Surface microstructure and element compositions in the coating after cavitation test were analyzed by SEM. The results showed that the loss of weight of conventional coating is much larger than nanostructured one and it indicates that the toughness of nanostructured coating is much stronger than conventional one.Considering the results of the above tests all-around, technical parameters of HVOF were selected, and excellent nanostructured coatings were deposited. The coating demonstrated not only high hardness but also strong toughness, and excellent anti cavitation erosion properties. It is expected that the nanostructured HVOF WC-12Co coatings will be used widely in hydro-equipments of Hydraulic turbine soon.