Abstract：To enhance the wear and corrosion resistance of the key functional surfaces of the non-magnetic drill collar, a non-magnetic WC-Ni-based composite coating was deposited on the P550 non-magnetic steel surface using laser cladding technology. The microstructure, electrochemical corrosion characteristics, and evolution of corrosion products of coatings under different simulated drilling fluid environments were analyzed using characterization methods such as potentiodynamic polarization, electrochemical impedance spectroscopy, SEM, XRD, and EDS. The results show that the WC-Ni based coating is composed of WC and W2C hard phases, NiCu solid solution, and secondary carbide phases such as Ni3W3C, (Fe,Ni)23C6, and Cr7C3. It contains a typical mixed microstructure of columnar crystals, cellular crystals, and equiaxed crystals. Under different simulated drilling fluid environments, the self corrosion current density of the coating is significantly lower than that of the substrate. Comparably, its self corrosion potential and pitting corrosion potential are positive, the polarization resistance is greater and the passivation film capacitance is smaller. The corrosion resistance performance of the coating is generally superior to that of P550 non-magnetic steel. When the pH values of the solution are 5, 7, 9 and 11, the corrosion resistance of the coating shows a trend of first increasing and then decreasing. The corrosion is lightest in weakly alkaline environments (pH=9), but is intensified in acidic (pH=5) and strongly alkaline (pH=11) environments due to the destruction of the passivation film. When the simulated drilling fluid temperatures are 20, 40, 60 and 80 ℃, the corrosion resistance of the coating decreases with increasing temperature. The increase in temperature significantly accelerates Cl- diffusion and interfacial reaction, leading to a decrease in the stability of the passive film and an increase in the corrosion rate of the coating. The results can provide theoretical basis and technical support for the performance optimization and engineering application of surface protective coatings on non-magnetic drill collars.
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2026, Vol. 31 
