ISOTHERMAL OXIDATION BEHAVIOR OF ELECTROSPARK DEPOSITED NiCrAlY COATINGS ON A NI-BASED SINGLE-CRYSTAL SUPERALLOY

The isothermal oxidation behavior of a NiCrAlY coating prepared by means of electrospark deposition (ESD) technology on second-generation Ni-based single-crystal DD6 was investigated at 1100 degrees C for 100 h. Surface morphologies, chemical composition, and the phase constitution of the coating were analyzed by scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS) and X-ray diffraction (XRD). The results showed that the as-deposited NiCrAlY coating, with uniform superfine columnar crystals and nanocrystallines. consists of beta-NiAl and gamma-Ni double phases; the oxidation resistance of the DD6 alloy was greatly improved by depositing the NiCrAlY coating, which was covered by two layers of oxides, theta-Al2O3 and alpha-Al2O3, while three layers of oxides, including Ni(Co)O, NiCr2O4, CrTaO4, CoTa2O6 and alpha-Al2O3, formed on the DD6 superalloy; the interdiffusion zone (IDZ) and secondary reaction zone (SRZ) formed between the NiCrAlY coating and the DD6 superalloy substrate for the interdiffusion; however, no deleterious Kirkendall voids appeared, which may be mainly due to the gradient transition of the elements between the coating and the substrate.