Properties Of CeO₂ Modified Dual-scale WC-10Co-4Cr Coating And Its Cavitation-erosion Behavior

Cavitation-erosion is a common failure form of flow passage components,widely existed in ship propeller,stern shaft and the power mechanical flow passage components of marine engineering equipment,which has become a key issue affecting the working efficiency and service life of these components.The development and application of cavitation-erosion resistance coating based on surface technology is an effective way to solve the cavitation-erosion failure of flow passage components.High-velocity oxygen-fuel（HVOF）spraying technology is an effective method to preparing high performance cavitation-erosion resistance coatings.This dissertation compared the cavitation-erosion behavior of thermal sprayed carbide coatings,analyzed the influence of the composition,microstructure and mechanical properties of the materials on the cavitation-erosion resistance performance,selected the excellent cavitation-erosion resistance of WC-10Co-4Cr coating to improve through CeO₂modified and dual-scale microstructure design to further increase its microstructure and mechanical properties,improve the cavitation-erosion resistance.The main research results of this dissertation are as follows:（1）Single micron scale four kinds of thermal sprayed carbides,WC-10Co-4Cr,WC-12Co,WC-17Co and Cr₃C₂-Ni Cr were prepared by HVOF,compared and analyzed the cavitation-erosion resistance of the coatings in deionized water and 3.5wt.%NaCl solution,and the micron WC-10Co-4Cr coating with excellent cavitation-erosion resistance was selected as the coating material for subsequent research.（2）Based on the structure of micron WC-10Co-4Cr powder,designed by CeO₂modified and dual-scale structure,CeO₂modified dual-scale WC-10Co-4Cr powder was prepared by agglomeration sintering method.The 1 wt.%CeO₂（particle size less than 50 nm）was added into the powder,and WC consisted of 70 wt.%micron WC（particle size about 2.5μm）and 30 wt.%nano WC（particle size about 100～200nm）.（3）CeO₂modified dual-scale WC-10Co-4Cr coating and Dual-scale WC-10Co-4Cr coating was prepared by HVOF.Compared with the micron WC-10Co-4Cr coating and the dual-scale WC-10Co-4Cr coating,the addition of CeO₂in CeO₂modified dual-scale WC-10Co-4Cr coating can effectively inhibit decarburization and oxidation,while the coating has dense structure,low porosity（0.55%）,high hardness and toughness(1348 HV_0.3,6.3 MPa·m^1/2).A continuous and stable passivation film formed on the coating surface in 3.5 wt.%NaCl solution,which had better corrosion resistance.（4）CeO₂modified dual-scale WC-10Co-4Cr coating presented better cavitation erosion resistance.The cavitation-erosion failure model of the WC-10Co-4Cr coating in deionized water was as follows:the matrix phase at the surface defects were removed first and fatigue micro-cracks appeared;cracks then propagate along the boundary of the hard phase.The hard phase particles fall off caused by the erosion of the matrix phase.The intersection of crack propagation leads to the spalling of the coating layer.（5）CeO₂modified dual-scale WC-10Co-4Cr coating produces a partially high binding strength oxidation layer（WO₃and Cr₂O₃）in 3.5 wt.%NaCl solution,which can seal surface defects and form a dense surface structure,prevent the direct impact caused by cavitation-erosion from destroying the coating.The cavitation-erosion failure model of the modified coating in 3.5 wt.%NaCl solution was as follows:the matrix phase at the surface defect was preferred to be removed,and the oxidation product layer resulting in the surface to form a dense structure;the matrix phase was removed,then the hard phase particles were exposed,and partially oxidation（WO₃and Cr₂O₃）still existed on the surface under cavitation-erosion;the hard particles fall off and the oxide layer was formed on the fresh coating surface.（6）The dual-scale structure on improving the microhardness of the CeO₂modified dual-scale WC-10CO-4Cr coating was more significant,and the CeO₂modified can improve the microstructure,and effectively increase the fracture toughness of the coating.Both CeO₂modification and dual-scale structure of the modified coating can effectively improve the microstructure and mechanical properties of the coating,which caused the modified coating has excellence cavitation-erosion resistance.