Study On Cavitation Resistance Of Different Structures WC-CoCr Coatings Sprayed By HVOF

Cavitation is widespread in the offshore platform,marine machinery,energy generation and other fields.Cavitation erosion has a tremendous impact on the fluid machinery,that leads to the sharp decrease in material strength and initial failure.Nowadays using surface engineering technology and advanced coating materials to prepare anti-cavitation coatings on the surface of the components is one of the main ways to solve the cavitation problem.Nanostructured,micro-nanostructured and conventional cermet powders have been sprayed to form six types of WC-10Co-4Cr coatings with both the high velocity oxygen-liquid fuel?HVOLF?process and the high velocity oxygen-gas fuel?HVOGF?process.Scanning electron microscopy?SEM?,optical microscopy?OM?and X-ray diffraction?XRD?have been used to analyze the microstructures of the coatings.The porosity,microhardness,fracture toughness and electrochemical property of the coatings were measured.The cavitation experiments of the coatings were carried out in fresh water and 3.5%NaCl solution.The anti-cavitation properties of different structure coatings were compared and the anti-cavitation mechanism was discussed.The result suggested that the HVOLF sprayed WC-10Co-4Cr coatings had well defined structures,and the main phases were WC and W₂C.However,the decarburization of the HVOGF sprayed nanostructured coating was pretty serious and a certain amount of W phase occurred.The particles of the three types HVOGF sprayed WC-10Co-4Cr coatings were deformed more fully and the coating structures were denser.Mircohardness,porosity and fracture toughness were significantly better than those of the HVOGF sprayed.The porosity,microhardness,fracture toughness and corrosion resistance of the coatings with different structures are quite different.The result of cavitation experiments demonstrated that the anti-cavitation performances of the HVOLF sprayed were better than that of the HVOGF sprayed.The micro-nanostructured coating deposited by fuel type process showed the best cavitation resistance in two test media.The cavitation resistance of nanostructured coating deposited by Gas type process was the worst.HVOF process,powder structure and test medium all have certain effects on the anti-cavitation property.The mass loss rate of coatings in fresh water could be expressed by a mathematical formula,R=2.5006-0.0013Hc-0.1522Kc,and the main influencing factor is the microstructure.The HVOLF sprayed micro-nanostructured coatings show the most excellent anti-cavitation performance respectively in two test media,due to the multi-scale coating structure.The poor performance of nanostructured coating is associated with the CoCr bond phase's little protective effect on hard phase.It is indicated that the selected processes are not suitable for the preparation of nanostructured anti-cavitation coatings.More attention should be paid to the research on multi-scale powder in anti-cavitation field.