Investigation of Hot Corrosion Behavior of Single and Dual Layered Zirconia Thermal Barrier Coatings in Calcium Magnesium Aluminosilicate Environment

Improvement of hot corrosion resistance in calcium magnesium aluminosilicate environments is one of the new main goals in development of turbine industries especially thermal barrier coatings (TBCs). The purpose of this research is to improve the quality and efficiency of YSZ thermal barrier coating in calcium magnesium aluminosilicate environments through replacing YSZ/CSZ composite layer. For this purpose, single layer YSZ and dual layer YSZ/CSZ TBCs deposited with atmospheric plasma spray (APS) technique on Ni-based superalloy (IN738LC) substrates as a top coat with a CoNiCrAlY bond coat. Hot corrosion resistance of the samples was investigated in a cyclic mode in which after each 4 h exposure to calcium magnesium aluminosilicate salts at 1150°C. The results of microstructural and phase studies of coatings by FESEM/EDS and XRD analysis before and after hot corrosion tests showed better resistance to dual layer YSZ/CSZ than single layer YSZ coatings and could act as barrier for the corrosive calcium magnesium aluminosilicate salts penetration into the TBC. Also, destruction of TBCs in calcium magnesium aluminosilicate environments due to infiltration of molten salts into the TBCs during hot corrosion process and cause the transformation of tetragonal zirconia to monoclinic phase during cooling.