Corrosion–Wear Synergistic Effect of Laser-Clad WC/Ni-Based Protective Coatings on P550 Nonmagnetic Drill Collar

The coupled corrosion–wear damage of P550 nonmagnetic drill collars severely restricts their service reliability in downhole environments. However, the asymmetric synergistic interaction between corrosion and wear, and the underlying microscopic damage mechanism of P550 steel and its laser-clad protective coating under saturated brine drilling fluid conditions remain insufficiently understood. In this work, nonmagnetic WC/Ni-based protective coatings were fabricated on P550 substrates by laser cladding. Three groups of comparative tests, including pure corrosion, pure wear and corrosion–wear tests, were performed in saturated brine drilling fluid. The results show that the P550 substrate undergoes severe material degradation, while the WC/Ni-based coating exhibits superior corrosion and wear resistance benefiting from the skeleton-support and load-bearing effect of hard WC particles. Volumetric loss quantification demonstrates that the total material loss of the coating is markedly lower than that of the substrate, and the volume loss of both substrate and coating is dominated by pure mechanical wear and corrosion-accelerated wear, whereas pure corrosion and wear-accelerated corrosion make negligible contributions. Of the two coupled damage modes, corrosion-accelerated wear is much more pronounced than wear-accelerated corrosion, showing an obvious asymmetric synergistic damage in this system. Microscopic analysis indicates that surface microstructure deterioration and microdefect propagation are the primary drivers aggravating the coupled corrosion–wear damage. In summary, the laser-clad WC/Ni coating can substantially enhance the corrosion–wear resistance of P550 nonmagnetic drill collars. This work provides theoretical reference and engineering support for surface strengthening and service-life extension of nonmagnetic drill collars.