Study On The Surface Micro-corrosion Behavior Of Copper-Nickel Alloy Pipes For Ships

Condenser is the core device of modern ship power system.Corrosion failures often occur due to the long-term transportation of the cooling medium-seawater with coppernickel alloy pipes for condensers,leading to frequent failures of the ship's power system,which is a major safety issue that needs to be resolved urgently.The research on the relationship between the surface corrosion behavior and microstructure of copper-nickel alloy pipes for marine condensers can provide necessary theoretical basis for further improving the surface corrosion resistance of copper-nickel alloy pipes,and can also provide important data for optimizing the preparation and processing technology of such pipes.In this paper,using energy spectrum analysis(EDS)or electron backscatter diffraction(EBSD)based on scanning electron microscopy(SEM),atomic force microscope(AFM),metallurgical microscope(OM)and other analytical instruments,through positioning tracking technology,reveal the corrosion behavior and corrosion morphology evolution law of the heat-treated CuNi10Fe1.6Mn copper nickel alloy;use electrochemical workstation and Raman spectroscopy to analyze the difference in surface corrosion behavior of coppernickel alloy pipes and the changes in element content and composition,and explore the inherent corrosion resistance of copper-nickel alloys mechanism.The main research results are summarized as follows:1.Through the artificial seawater immersion experiment on the copper-nickel alloy pipe samples after heat treatment,it is found that the microscopic corrosion behavior of the sample surface is closely related to the grain orientation.The pitting pits extend from the grain boundary to the inside of the grain.The analysis using the oxygen atom adsorption model shows that the corrosion products of the grains oriented closer to the<0 0 1>direction are more uniform and dense,and the number of pitting pits is higher than that of the grains close to the<111>and<1 0 1>directions.The main components of surface corrosion products are Cu2O and Cu2(OH)3C1.2.Based on the SEM-EBSD and AFM positioning and tracking technology,the relationship between the surface corrosion morphology of copper-nickel alloy pipes and the grain orientation is studied,and it is found that the angle between the grain orientation and the<1 1 1>direction is different.Decrease,the corrosion depth of the grain surface increases,and the corrosion morphology changes from a scallop shape to a step shape or a tetrahedral convex shape.The use of step growth model(TLK)analysis shows that the smaller the angle between the grain orientation and the<1 1 1>direction,the higher the surface energy of the grain,and the corrosion will occur first,and the corrosion rate is higher than that of the lower energy crystal.As a result,the surface of the grains shows three corrosion morphologies:scallop-shaped,step-shaped and tetrahedral convex shaped.3.The corrosion morphology and corrosion resistance of the copper-nickel alloy pipe samples after the EBSD experiment were analyzed,and it was found that compared with the copper-nickel alloy pipe samples without the EBSD experiment,there were fewer surface corrosion products,more positive corrosion potential,and corrosion current.smaller.SEMEDS and Raman analysis show that the surface of the copper-nickel alloy sample subjected to the EBSD experiment is more likely to form corrosion products such as NiO and Cu2O due to the electron irradiation effect,and the protection of the matrix is stronger during the corrosion process,so the corrosion resistance performance is better.