Cyclic oxidation behavior and thermal barrier effect of YSZ–(Al2O3/YAG) double-layer TBCs prepared by the composite sol–gel method

Novel YSZ (6 wt.% yttria partially stabilized zirconia)–(Al2O3/YAG) (alumina–yttrium aluminum garnet, Y3Al5O12) double-layer ceramic coatings were fabricated using the composite sol–gel and pressure filtration microwave sintering (PFMS) technologies. The thin Al2O3/YAG layer had good adherence with substrate and thick YSZ top layer, which presented the structure of micro-sized YAG particles embedded in nano-sized α-Al2O3 film. Cyclic oxidation tests at 1000 °C indicated that they possessed superior properties to resist oxidation of alloy and improve the spallation resistance. The thermal insulation capability tests at 1000 °C and 1100 °C indicate that the 250 μm coating had better thermal barrier effect than that of the 150 μm coating at different cooling gas rates. These beneficial effects should be mainly attributed to that, the oxidation rate of thermal grown oxides (TGO) scale is decreased by the “sealing effect” of α-Al2O3, the “reactive element effect”, and the reduced thermal stresses by means of nano/micro composite structure. This double-layer coating can be considered as a promising TBC.