Tuning the Microstructure and Tribocorrosion Behavior of Laser Cladding CoCrFeNiMo 0.5 Ti 0.4 High‐Entropy Alloy Composite Coatings by Varying the hBN Content

To repair oil drill pipe joints that failed due to corrosion and wear under marine and oil‐and‐gas service conditions, a hBN‐reinforced CoCrFeNiMo 0.5 Ti 0.4 high‐entropy alloy composite coatings were deposited on 42CrMo steel using laser cladding. The effects of hBN content on microstructure, mechanical response, tribocorrosion, and electrochemical corrosion in 3.5 wt% NaCl were investigated. The results reveal a nonmonotonic hBN effect, with 2 wt% as the optimal addition. At this content, partial hBN decomposition promotes in‐situ TiN/TiB 2 precipitation and grain refinement, while the matrix evolves from an FCC/BCC dual‐phase structure toward an FCC‐dominant structure with a higher fraction of high‐angle grain boundaries. This coordinated microstructure improves load support and interfacial stability. The optimized coating shows the lowest tribocorrosion rate of 0.6808 μm 3 ·N −1 ·mm −1 , corresponding to reductions of 95.72% and 88.83% relative to 42CrMo and the hBN‐free coating, respectively. The tribocorrosion mechanism is characterized by protected mild abrasive wear, as oxides and residual hBN form a stable interfacial layer that suppresses Cl − ingress and corrosion–wear coupling. Electrochemical tests further confirm improved corrosion resistance, as indicated by the lowest corrosion current density, highest charge transfer resistance, sparse pitting, and minimal oxygen enrichment after polarization.