Microstructure and Corrosion Properties of Al₂O₃/Ni-W-Fe Chemical Coatings Assisted by Ultrasonic for Oil and Gas Pipelines

Ni-W-Fe coating with nano-Al₂O₃ particles was prepared on the surface of Q195 steel for oil and gas pipelines by ultrasonic assisted technology. The microstructure and corrosion properties of the coating were studied by experimental testing. The results show that the microstructure of Ni-W-Fe coating has obvious amorphous characteristics,and the microstructure presents a closely connected continuous cell distribution.Adding nano Al₂O₃ particles in the composite coating,there are a large number of dispersed small particles.Adding Al₂O₃ particles can also be used as a nucleation point for coating growth,promote grain growth,and eventually form fine microstructure grains. The hardness and porosity of the composite coatings treated by ultrasonic assisted treatment are lower than those treated by magnetic stirring. Magnetic stirring and ultrasonic assisted can reduce the corrosion rate of the coating,and the corrosion resistance of the composite coating is improved obviously after adding Al₂O₃ particles. Ni₃S₂ products are formed on the surface of the coating,which can play an excellent protective effect on the matrix. Microcracks form in the corrosion zone of the coating,and the convex structure disappears. After corrosion,the coating and matrix show a tight bond state. The contents of Ni,Si and W are basically the same,so it can be inferred that the coating can play an excellent protective role on the matrix after corrosion.