Abstract
The purpose of this research is to improve the quality and efficiency of yttria-stabilised zirconia (YSZ) thermal barrier coating (TBC) through replacing CSZ. Three types of top coats including conventional YSZ, CSZ and nanostructured Al2O3/CSZ composite were applied, by thermal spray technique, on IN738LC base metal and the results were compared to one another. In the present investigation, hot corrosion behaviours of the coatings were tested in a furnace containing a mixed environment of Na2SO4 and V2O5 salts at 1050°C. Nanoindentation tests were used to evaluate mechanical properties of the coatings. The experimental results confirmed that nanostructured Al2O3/CSZ composite coating had much hot corrosion resistance than those of conventional TBCs. The transformation of tetragonal zirconia to monoclinic ZrO2 and formation of YVO4 and CeVO4 crystals as hot corrosion products led to the degradation of the mentioned TBCs. Microstructural analysis indicated that the penetration of molten salt was much less in the nanostructured Al2O3/CSZ composite coating where the infiltration of both oxygen and aggressive molten salt was reduced. Mechanical results showed that the superior mechanical properties of nanostructured Al2O3/CSZ composite coating may be attributed to its structural stability.