Enhancing the oxidation resistance of P91 alloy with Al ₂ O ₃ and Cr ₂ O ₃ coating at high temperature

This study examines the surface modification of P-91 ferritic steel using Al2O3 and Cr2O3 coatings to enhance high-temperature oxidation resistance. The objective is to develop stable, adherent, and protective oxide layers that minimise oxidation-induced degradation in industrial environments. Bare and coated specimens were subjected to isothermal oxidation at 650°C and 750°C in a controlled CO2+O2 atmosphere. Oxidation kinetics were evaluated using gravimetric analysis, while SEM and XRD techniques characterised morphology, phase composition, and coating integrity. Results show that both Al2O3 and Cr2O3 coatings significantly improve oxidation resistance. The alumina coating demonstrated superior performance, forming a continuous, dense, and adherent scale that effectively restricted oxygen diffusion at both temperatures. Chromia coatings also enhanced resistance, but to a lesser extent. In contrast, uncoated P-91 developed porous, non-protective oxide scales mainly consisting of Fe3O4, Fe2O3, and (FeCr)3O4 prone to spallation and cracking. Overall, alumina proved the most stable high-temperature diffusion barrier.