Durability of TBCs with a surface environmental barrier layer under thermal cycling in air and in molten salt

In order to protect the thermal barrier coatings (TBCs) from oxidation and hot corrosion attack, several barrier coatings on top of the yittria-stabilized zirconia (YSZ) TBC have been evaluated. Thermal cycling tests in air and hot corrosion resistance tests in molten Na2SO4 were used to determine the durability of these coatings. Barrier layers investigated include mullite (3Al2O3·2SiO2), BAS (BaO·Al2O3·2SiO2) and calcium silicate (1.8CaO·SiO2). Mullite and BAS barrier coatings showed the best promise as potential hot corrosion barriers. TBCs with mullite or BAS barrier showed life similar to that of standard YSZ TBC under thermal cycling in air, while demonstrating the ability to limit seepage of salt into YSZ in hot corrosion test. In order to avoid the coating damage due to seepage of salt through the edge, there is a need to examine the hot corrosion resistance on coupons that are completely enclosed by the coating.