Microstructure and properties of plasma-sprayed AlCoCrFeNi high-entropy alloy coatings via CeO2 doping

High-entropy alloy coatings fabricated by atmospheric plasma spraying (APS) often exhibit inherent defects such as porosity and weak interlayer bonding. To address this, high-performance AlCoCrFeNi HEA composite coatings were successfully fabricated on Q235 steel substrates via a rare earth CeO2 doping strategy. A systematic investigation was conducted on the influence of CeO2 doping content (3–20 wt%) on the phase composition, microstructure, wear resistance, and corrosion resistance of the composite coatings. The results demonstrate that the optimal CeO2 addition (5 wt%, HC5) significantly refines HEA grains, reduces coating porosity to 1.24 %, and enhances adhesion strength to 35.18 MPa. This densified microstructure and superior mechanical properties collectively lead to significant improvements in both wear and corrosion resistance. The HC5 coating exhibits the lowest friction coefficient (0.51) and the lowest corrosion current density (5.644 × 10−6 A cm−2). However, a further increase in CeO2 content leads to microstructural heterogeneity within the coating due to CeO2 agglomeration. The aggregated CeO2 particles act as brittle crack initiation sites under tensile loading, resulting in significant deterioration in adhesion strength, microhardness, and corrosion-wear resistance. This work establishes 5 wt% CeO2 as the optimal concentration for enhancing APS-processed AlCoCrFeNi HEA coatings, providing foundational insights for their application in protecting Q235 steel under aggressive conditions.