Microstructure and oxidation resistance of magnetron-sputtered nanocrystalline NiCoCrAlY coatings on nickel-based superalloy

Nanocrystalline NiCoCrAlY coatings on GH3128 nickel-based superalloy were produced using DC magnetron sputter deposition with a composite target. The microstructure and morphology of coatings were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX) and atomic force microscopy (AFM). Isothermal-oxidation tests were performed at 1100 oC in air for 24 h. The results show that the magnetron-sputtered NiCoCrAlY coating possesses a polycrystalline austenitic structure (FCC) with lattice constant 0.359821 nm. The (2 2 0) is the preferred growth direction of the NiCoCrAlY coating and the coating grain size is about 70 nm. The isothermal-oxidation test results exhibit that the oxidation kinetics of substrate and coating specimens all basically follow the parabolic rate law. However, the weight gain rate constant of coating is only about one-fifth of that of substrate. The weight gain of NiCoCrAlY coated specimen is only 48.16% of the superalloy substrate specimen after the isothermal-oxidation test. The above results reveal that the magnetron-sputtered nanocrystalline NiCoCrAlY coating is quite effective to increase the high temperature oxidation resistance of GH3128 superalloy.