A novel YSZ-YSZ/Al 2 O 3 (YSZ means 6 wt% yttria partially stabilized zirconia) double-layer thermal barrier coating was fabricated using composite sol-gel and pressure filtration microwave sintering (PFMS) technologies. In this double-layer coating, the top layer was YSZ ceramics with a thickness of about 150 lm and the bottom layer was composed of micro-sized YSZ particles packed by nano-sized a-Al 2 O 3 films and had a thickness of about 10 lm. Cyclic oxidation tests indicated that this coating possessed superior properties to resist oxidation of alloy and spallation of coating. These beneficial effects could be mainly attributed to that, the alloy substrate could be sealed completely by a-Al 2 O 3 phase and the thermal stress could be decreased by means of better thermal matching and nano/ micron structure in YSZ/Al 2 O 3 layer. Moreover, thermal insulation capability tests indicated that the thermal barrier effect was improved due to the application of YSZ/Al 2 O 3 layer. YSZ/Al 2 O 3 layer could be considered as a promising bond coat in TBCs.

In this study, a novel sol-gel process has been utilized to fabricate Al 2 O 3 /YSZ (6 wt% yttria partially stabilized zirconia) composite coatings on Ni-based superalloy. The green coatings were obtained by electrophoretic deposition (EPD) in a suspension containing aluminium oxide sol, nano-Al 2 O 3 and micro-YSZ particles, and then treated by so-called pressure filtration microwave sintering (PFMS) process. The as-sintered composite coatings were dense, uniform and crack-free and the phases mainly present a-Al 2 O 3 , m-ZrO 2 and t-ZrO 2 as aluminium oxide sol content decreasing. The cyclic oxidation tests at 1000°C for 200 h demonstrate that both of high-temperature oxidation and spallation resistance for the coated samples were remarkably improved. These beneficial effects could be attributed to the special microstructure that micro-YSZ particles embedded in nano/ submicron Al 2 O 3 matrix. Meanwhile, the mechanisms of the inhibition of the oxygen diffusion and thermal match are further discussed.