深海静水压力对环氧涂层/907A低合金钢体系失效行为的影响OA北大核心CSTPCD

Applying coatings on metal surfaces is one of the most effective ways to protect metals.In the field of marine corrosion protection,epoxy glass flake coatings with lamellar structures that hinder the transmission of corrosive media have been extensively explored and used.The work aims to investigate the failure behavior and failure mechanism of the coatings under deep-sea hydrostatic pressure.The epoxy glass flake coating/907A low alloy steel system was immersed by the simulation test device of the deep-sea environment.The failure mechanism of the coating/metal system was analyzed from the perspectives of EIS,wet adhesion,cathodic delamination diameter,chemical structure and microscopic morphology of the coatings,microscopic morphology of the metal surface before and after rust removal,and corrosion products of the metal.EIS was used to test the anti-corrosion properties of the coatings.Following the ASTM D4541,a pull-off adhesion tester was used to test wet adhesion,and the diameter of the alloy was 20 mm.At the end of the test,the impedance values of the coatings decreased to 3.83×106 Ω·cm2 and 6.28×104 Ω·cm2 at 0.1 MPa and 15 MPa hydrostatic pressure,respectively.The wet adhesion of the coatings from original 6.52 MPa decreased to 2.76 MPa and 2.31 MPa and the wet adhesion loss values were 57.67% and 64.57%,respectively.The cathodic delamination diameter of the coatings increased by 1.2 mm and 1.5 mm under 0.1 MPa and 15 MPa hydrostatic pressure,respectively.At the initial stage of immersion,the diffusion process of water in the coatings conformed to Fick 's diffusion law,and the diffusion coefficients of water in the coating increased from 1.05×10-9 cm2/s to 2.39× 10-9 cm2/s under 0.1 MPa and 15 MPa hydrostatic pressure.Small pores and cracks appeared on the coating surface under 0.1 MPa hydrostatic pressure,while the pores on the coating surface were more obvious and small bubbles appeared on the coating surface under 15 MPa hydrostatic pressure.Uniformly distributed corrosion products were observed on the surface of the metal under 0.1 MPa hydrostatic pressure.Under 0.1 MPa hydrostatic pressure,small amounts of corrosion products were observed on the metal surface and γ-FeOOH had the highest percentage in the corrosion products and the maximum corrosion pit diameter after rust removal was about 15 μm.Under 15 MPa hydrostatic pressure,multiple corrosion products were observed on the metal surface.In the corrosion products,there was a significant increase in the amount of Fe3O4 which had high electrochemical activity and an extensive decrease in the amount of γ-FeOOH,and the diameter of corrosion pits after rust removal was about 25 μm.The analytical results indicate that corrosive media such as water and oxygen can accelerate diffusion into the coating/metal interface under high hydrostatic pressure,leading to a further decrease in the wet adhesion of the coatings,an increase in the cathodic delamination diameter of the coatings,and a more serious coating failure.At the same time,high hydrostatic pressure can promote the formation of Fe3O4 with high electrochemical activity in the corrosion products,which leads to more serious metal corrosion.In addition,the main reason for the failure of the coatings under high hydrostatic pressure is the destruction of its physical structure.