Research On Cavitation Erosion Resistance Of Ni-based Alloy Sprayed And Fused Coatings In Marine Environment

Cavitation exists widely in overflowing components of fluid machineries such as centrifugal pump?transfer pump in the offshore platform and ship propeller?cylinder liner and etc.Cavitation causes not only huge economic loss but also potential safety hazard.Due to the cavitation erosion occurs only in the surface of the parts,the coating technology to improve the surface performance of overflowing components is an important method to solve the problem of cavitation erosion of marine engineering equipment's key-module.Ni-based alloy with good cavitation erosion resistance and excellent manufacturability is widely used for cavitation erosion resistant coating materials.Nibased self-fluxed alloy is the most widely used Ni-based alloy,including NiCrBSi series,the series of WC reinforced Ni base,NiCrBSiMoCu series and so on.The sprayed and fused coatings of Ni60A?NiWC35?Ni55MoA and Ni60 CuMo alloy were prepared by oxy-acetylene flame spraying and fusing.X-ray diffraction(XRD)and Scanning electron microscopy(SEM)have been used to analyse the microstructures of the coatings,the Rockwell hardness and electrochemical properties of the coatings were measured.The cavitation experiments of the coatings were carried out in 3.5% NaCl solution and distilled water respectively,the anti-cavitation properties of different coatings were discussed and the anti-cavitation mechanism was analysed.The results showed that the NiCrBSiMoCu coatings had well defined structures and good corrosion resistance.There were diffusely distributing WC particles in WC reinforced Ni-based coating,although the hardness of WC reinforced Ni-based alloy coating was enhanced because of the adding of WC particles,the corrosion resistance was greatly reduced.The result of cavitation experiments demonstrated that the anti-cavitation performance of the two NiCrBSiMoCu coatings in NaCl solution were excellent and increased by 24% and 39% on the basis of NiCrBSi coating;the cavitation resistance of WC reinforced Ni-based alloy coating in NaCl solution was the worst and reduced 28% on the basis of NiCrBSi coating.The structures of Ni-based alloy coatings are different because of the different varieties and content of element in Ni-based alloy powders,leading to the different anti-cavitation performance of the coatings.Although the cavitation erosion process of four kinds of coatings is that the extension of cavitation erosion crack lead the particles on the surface to peel off and produce corrosion pits,the expansion of the crack is relatively difficult in NiCrBSiMoCu series coatings(especially Ni60CuMo)which has tiny structure and the pits on their surface are smaller and lighter,so they have good anti-cavitation performance in NaCl solution.Relatively the pits on the NiCrBSi alloy coating are larger and deeper,which makes the cavitation performance worse in NaCl solution.There are large size WC hard phase in WC reinforced Ni-based alloy coating,WC particles and Ni-based solid solution can form strong battery,which lead to the dissolve of Ni-based solid solution in WC boundary and accelerate the expansion of the interfacial crack greatly,finally WC particles fall off and the Ni-based solid solution around WC particles is easily to be damaged and peel off,the surface of the coating has the biggest pits and the uneven shape around it.So it has the worst anti-cavitation performance in NaCl solution.