Excellent self-lubricating performance of a novel cermet composite coating at 600–800 °C: Synergistic construction of multifunctional tribofilms via laser texturing and solid lubricants

To overcome the high coefficients of friction (COF>0.5) of Cr₃C₂ NiCr cermet coatings at 600-800 °C and address the poor activity of the single BaF₂/CaF₂ lubricant below 700 °C. Herein, we develop a Cr₃C₂-NiCr-(BaF₂/CaF₂)-Bi₂O₃ composite coating fabricated by thermal spraying, laser texturing, and vacuum Bi₂O₃ infiltration. It achieves average COFs of 0.27, 0.19, and 0.11 at 600, 700, and 800 °C—reductions of 59.7%, 70.8%, and 78.8% compared to Cr₃C₂-NiCr coating. Multi-scale characterization reveals a dual-gradient protective film that forms at high temperature: an outer molten Bi/Bi₂O₃ glaze layer providing fluid lubrication and debris entrapment, and an inner oxide layer (NiO/Cr₂O₃/BaCrO₄/CaCrO₄) that provides load-bearing, oxidation resistance, and low-shear assistance. This work establishes a design framework for durable, broad-temperature self-lubricating cermet coatings.