High‐Temperature Oxidation Properties of AlCoCrFeNiSi_x High‐Entropy Alloy Coatings by High‐Velocity Oxygen Fuel Spraying

AlCoCrFeNiSi_x high‐entropy alloy coatings (x = 0, 0.2, 0.4, 0.6, 0.8 at.%) are prepared on 316 L stainless steel by high‐velocity oxygen fuel spraying. The evolution of morphology and microstructures of the coatings as a function of Si content during high‐temperature oxidation is characterized using X‐ray diffraction, scanning electron microscopy, and energy‐dispersive spectroscopy. The volume ratio of Si elements in coatings increases from 1.88 to 11.02% as Si content in the feedstock increases from 0.2 to 0.8 at.%, and the continuous lamellar structures consisting of Si are found in the high‐Si coatings. The AlCoCrFeNi coating presents an undulation surface, and the oxide layer is discontinuous. The high‐Si coatings show flat surfaces with a continuous composite oxide layer consisting of Al₂O₃, Cr₂O₃, and SiO₂, primarily attributed to the third‐element effect of Si. The AlCoCrFeNiSi_0.8 coating exhibits the lowest mass gain of 3.84 mg cm⁻² after 100 h, showing a 57.0% reduction compared to the 8.94 mg cm⁻² of the AlCoCrFeNi coating. The findings provide a strategic pathway for designing the oxidation‐resistant high‐entropy alloy coatings via tailored element additions.