Study On Microstructure Characterization And Corrosion Resistance Mechanism Of Copper-Nickel Alloy Pipes For Ships

Condensers are very important components in modern ships,which are used in marine power systems,air conditioning and refrigeration systems.However,copper-nickel alloy heat transfer tubes in condensers often suffer from severe corrosion due to long-term transport of seawater as cooling medium.It is an urgent problem to be solved.Through the microstructural analysis of B10 and B30 copper-nickel alloy pipes for ship condensers,the relationship between corrosion resistance and microstructure of copper-nickel alloy pipes was revealed.It can provide the necessary theoretical basis for improving the corrosion resistance of copper-nickel alloys.And it can provide important data support for the optimization of this type of pipe preparation process.In this paper,metallographic examination(OM),energy spectrum analysis(EDS)and electron backscatter diffraction analysis(EBSD)based on scanning electron microscopy(SEM)were used to compare and analyze the B10 and B30 copper-nickel alloy tubes for ship condensers.The difference in microstructure between different batches or different batches of copper-nickel alloy tubing from the same source was evaluated by electrochemical analysis and testing techniques to evaluate the influence of the difference in microstructure between copper-nickel alloy tubing on its corrosion resistance.The SEM-based "positioning tracking" characterization technique was developed to observe the surface corrosion morphology and corrosion product evolution process of copper-nickel alloy tube,and to explore the internal mechanism of the influence of microstructure on the corrosion resistance of copper-nickel alloy.The main results for this study are summarized as follows:(1)The main microstructural factors of B10 copper-nickel alloy with good corrosion resistance were the grain size is larger,resulting in a relatively low grain boundary.This effectively reduced the number of channels through which the corrosive medium was transported to the interior of the substrate.This inhibited the amount of active atoms involved in corrosion in the corrosive medium.This reduced the rate of corrosion.The final performance was better corrosion resistance.(2)The main microstructural factors of B30 copper-nickel alloy samples with good corrosion resistance was high content of special grain boundaries,especially coherent twin boundaries.It effectively hindered the connectivity of random grain boundary networks and might form large-sized grain clusters,which in turn exhibited superior corrosion resistance.(3)The location tracking characterization showed that the<001>and<101>oriented grains in the B10 copper-nickel alloy tube samples were more resistant to corrosion.The results showed that the corrosion resistance of B10 copper-nickel alloy micro-region was closely related to crystal orientation.This might be caused by different corrosion potentials of different crystal orientations,resulting in better corrosion resistance of the grains with higher corrosion potential.(4)The location tracking characterization showed that there were corrosion cracking on the surface corrosion products of B10 and B30 copper-nickel alloy tube samples.The corrosion products were enriched with Fe,Ni and Mn elements to varying degrees,and more O and Cl elements.Corrosion morphology and product analysis results showed that the content of Ni in the B30 copper-nickel alloy tube matrix was higher,which leads to more Ni atoms filling into the Cu2O corrosion product film during the corrosion process,making the corrosion product film more dense.Finally,it showed better corrosion resistance at different corrosion stages.