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

- Sputtered β-NiAl coating on single crystal superalloy René N5 exhibited good oxidation resistance.
- The mechanism for the formation of SRZ in β-NiAl coated single crystal superalloy was analyzed.
- Arc ion plated-NiCrO interlayer was fabricated as active diffusion barrier between β-NiAl coating and N5 superalloy, which prevented the formation of IDZ and SRZ, and retarded the coating degradation effectively.
- The transformation of NiCrO interlayer into α-Al2O3/Metal/α-Al2O3 sandwich structure was also revealed.

Arc ion plated-NiCrO interlayer was fabricated as an active diffusion barrier for microcrystalline β-NiAl coating on Ni-base single crystal René N5 superalloy. The effects of the NiCrO barrier layer on the cyclic oxidation behavior at 1100 °C were investigated. The microstructure of coated specimens was characterized by SEM, XRD, XPS and TEM. The microcrystalline β-NiAl coating without NiCrO barrier layer exhibited good oxidation resistance by forming exclusive α-Al2O3 scales during cyclic oxidation tests at 1100 °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 α-Al2O3/Metal/α-Al2O3 sandwich structure during vacuum annealing at 1000 °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 NiAl coated single crystal superalloy and the mechanism for the transformation of NiCrO interlayer into α-Al2O3/Metal/α-Al2O3 sandwich structure were discussed.