Mechanistic investigation of aluminide coating formation by low-pressure chemical vapor deposition method on NiCoCrAlY coating in presence of nickel-ceria composite layer

In this study, a hybrid coating comprised of NiCoCrAlY fabricated by HVOF method, Ni-CeO2 composite coated by electrodeposition, and aluminide coating applied by low pressure chemical vapor deposition (LPCVD) method are investigated. To elucidate the formation process of aluminide coating, the microstructure and properties of the applied coatings were examined by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and EDS analyses. It was concluded that the desired beta-NiAl phases are uniformly created within a single step on the surface. Furthermore, with the extending of the coating duration from 2 to 4 h, the thickness of the aluminide coating was increased from 14 to 25 mu m. The thickness values were increased even further in the presence of Ni-CeO2 coating, where the growth mechanism was also changed. Within 4 h, a coating with a thickness of roughly 50 mu m was obtained. Moreover, in the presence of Ni-CeO2 coating, it was observed that the inward diffusion of aluminum was predominant at the beginning of the process, whereas with longer processing durations, the outward diffusion of the nickel becomes dominant instead.