Enhancement of hot corrosion resistance of thermal barrier coatings by using nanostructured Gd2Zr2O7 coating

Improvement of hot corrosion resistance in Na2SO4-V2O5 environments is one of the main goals in development of thermal barrier coatings (TBCs). In this study, nano-Gd2Zr2O7 (nano-GZ) powder was synthesized by co precipitation method and then deposited with atmospheric plasma spray (APS) technique on Ni-based superalloy (IN738LC) substrates as a top coat with a CoNiCrAIY bond coat. Hot corrosion behavior of nano-GZ coated samples were studied and compared with those of CoNiCrAlY/conventional YSZ coatings. Hot corrosion resistance of the samples was investigated in a cyclic mode in which after each 4 h exposure to Na2SO4-55 wt% V2O5 salts at 950 degrees C. The results indicated that nano-GZ coatings have better hot corrosion resistance compared to conventional YSZ coatings. It was found that micro-cracks and pores played a main role in the molten salts infiltration into the TBC5 during hot corrosion process. In the nano-GZ coating with nano zones structure which surrounded by fully molten parts could fill the aforementioned defects and could act as barrier for the corrosive molten salts penetration into the TBC. The main factor in destruction of the investigated coatings is the formation and growth of needle-like YVO4 and GdVO4 crystals, in both classes of the coatings.