A magnetron sputtered microcrystalline β-NiAl coating for SC superalloys. Part II. Effects of a NiCrO diffusion barrier on oxidation behavior at 1100 °C

Arc ion plated-NiCrO interlayer was fabricated as an active diffusion barrier for microcrystalline beta-NiAl coating on Ni-base single crystal Rene N5 superalloy. The effects of the NiCrO barrier layer on the cyclic oxidation behavior at 1100 degrees C were investigated. The microstructure of coated specimens was characterized by SEM, XRD, XPS and TEM. The microcrystalline beta-NiAl coating without NiCrO barrier layer exhibited good oxidation resistance by forming exclusive alpha-A1203 scales during cyclic oxidation tests at 1100 degrees C in air. However, the formation of thick interdiffusion zone (IDZ) and secondary reaction zone (SRZ), which accelerated coating degradation, was observed. The NiCrO barrier layer was transformed into alpha-Al2O3/Metal/alpha-Al2O3 sandwich structure during vacuum annealing at 1000 degrees C. The sandwich structure was adherent to the coating and the substrate, prevented the formation of IDZ and SRZ, and retarded the coating degradation effectively during cyclic oxidation tests. The mechanism for the formation of SRZ in NiAI coated single crystal superalloy and the mechanism for the transformation of NiCrO interlayer into alpha-Al2O3/Metal/alpha-Al2O3 sandwich structure were discussed. (C) 2017 Elsevier B.V. All rights reserved.