Effect of (Ag, Cu) powder strategy on microstructure and tribological properties of Ni-based Ag-containing composite coatings

To investigate the influence of different powder addition strategies on the properties of Ag-containing lubricating coatings, NiCrAlY-Mo-Ag-Cu coatings incorporating different (Ag, Cu) powders (direct doping, core-shell structure, and powder alloyed) were fabricated via atmospheric plasma spraying. Combining characterization techniques and density functional theory calculations, the friction behavior, tribological properties, and underlying mechanisms of the three coatings were explored through constant-temperature friction tests and thermal cycling friction tests over a wide temperature range. The results indicate that the core-shell structure process helps reduce coating porosity (from 2.61% to 1.68%), but the average hardness of the coating decreased by 12.5% (230.6 HV → 201.8 HV). The alloying strategy circumvented hardness degradation, striking a balance between coating densification and mechanical robustness. At 800 ℃, a composite tribofilm comprising simple metal oxides (e.g., NiO, Cr 2 O 3 , and Al 2 O 3 ) and high-temperature lubricating phases (NiMoO 4 , Ag 2 MoO 4 , CuMoO 4 ) developed on the surface, effectively suppressing silver agglomeration and depletion. Owing to the synergy of these effects, the AgCu-alloyed coating achieved a low coefficient of friction (COF) of 0.25 at 400 ℃ and demonstrated a ∼30.9% reduction in wear rate during the 800 ℃ thermal cycling test compared to the direct-doping coating.