Studies On B30 Copper Nickel Alloy Corrosion Product Film In Artificial Seawater

This work investigates the corrosion behavior of B30 copper nickel alloy during various immersion periods in artificial seawater by the electrochemical measurement, microstructure observation, composition analysis and nanoindentation analysis. Meanwhile, the fluid field in the vicinity of the sample surface is simulated with the aid of computer software (ANSYS CFX), revealing the relationship between the mechanical properties of the corrosion product film and the corrosion resistance in the process of dynamic seawater. It comprehensively evaluates the corrosion resistance of B30 copper nickel alloy in artificial seawater.Firstly, the corrosion behavior and film semi-conductivity, composition were investigated after various static immersion periods. The behavior of the film formation and rupture was specially studied to understand the relationship between the semiconductor features of the film and the corrosion resistance. The result shows that the corrosion product film is most dense and protective after the static immersion of about 50days. The double structure corrosion product film that the outer is n semiconductor, the inner is p semiconductor can effectively prevent the erosion of Cl- in the solution. It can reduce pittings and protect matrix well.The influence of impact angle and velocity on the corrosion behavior of B30 alloy was studied in various flux of artificial seawater by electrochemical impedance and noise combined with the flow field distribution analysis by ANSYS CFX computational fluid dynamics software. The result shows that the electrode surface fluid field strength is increasing, the impedance value falling down and the corrosion resistance decreasing with the increase of impact angle. The corrosion resistance is poor under the high flow velocity, and good under low velocity. Compared with charge transfer and mass transfer velocity,the shear force is the dominant factor with the increase of flow velocity, leading to the increase of the probability of film cracking and the increase of electrochemical activity. There exists a critical flow velocity between 3m/s and 5m/s.In order to further understand the relationship between the micro-mechanical property and the corrosion behavior related to the film cracking, nanoindentation and erosion-corrosion experiments were conducted for samples after artificial potentiostatic polarization of 250mV,300mV and immersed for 90 days. The result shows that the higher of the surface film mechanical properties, the lower the probability of film cracking, leading to the enhancedcorrosion resistance. The corrosion resistance of immersion for 90 days is the best, and the sample after potentiostatic polarization of 300mV is the worst. It can improve erosion resistance of surface film by increasing its elastic modulus, which provides reference for metal surface treatment technology.