Microstructure and initial stage oxidation of NiCoCrAlY coatings deposited by arc ion plating technique

The microstructure of the NiCoCrAlY coatings deposited by arc ion plating (AIP) and its oxidation mechanism at initial stage were investigated by XRD, SEM, TEM and photostimulated luminescence spectroscopy (PSLS). The results showed that as-deposited NiCoCrAlY coatings were composed of nano-grains and possessed apparent layered structure. After vacuum annealing, the layered microstructure disappeared and the coating became much denser. The nano-grains in the coatings became much larger and twinned grains appeared. In addition, a very thin oxide scale mainly of alpha-Al2O3 formed on the coating surface after annealing. In the subsequent initial oxidation stages, transient theta-Al2O3 increased and then turned into stable alpha-Al2O3. The related mechanism was also discussed.