An in-situ oxide-dispersion-strengthened AlCoCrFeNiY high-entropy alloy composite coating prepared by AC-HVAF with superior oxidation and spallation resistance

We report an in-situ oxide-dispersion-strengthened AlCoCrFeNiY high-entropy alloy composite coating (ODS-HEA composite coating) with exceptional oxidation and spallation resistance at 1100 °C and 1150 °C. The coating is manufactured by activated combustion-high velocity air fuel (AC-HVAF) and has an ultrafine-grained microstructure that comprises γ, β and nanoscale oxide particles (Al2O3, Cr2O3 and Y2O3) formed in-situ in coating processing. The thermally grown oxides (TGOs) on the coating at 1100 °C and 1150 °C are exclusively α-Al2O3 with a columnar grain structure. The parabolic rate constant of the coating is about half of that of the conventional NiCoCrAlY coating (CNA coating) at both 1100 °C and 1150 °C, respectively. The lower TGO growth rate is primarily attributed to its coarser TGO grains that reduce the efficient oxygen diffusivity. Compared to the CNA coating, a higher TGO/coating interfacial toughness is achieved via inhibiting the formation of interfacial pores for ODS-HEA composite coating. The low TGO growth rate decreases the driving force for TGO spallation and the high interfacial toughness increases the TGO adhesion, thus contributing to the strong spallation resistance for the ODS-HEA composite coating. The superior oxidation and spallation resistance of the ODS-HEA composite coating at 1100 °C and 1150 °C make it a candidate bond coat for advanced thermal barrier coatings.