Fibers and sol-gel matrix based thermal barrier coating systems for outstanding durability

Conference Dates

June 24-29, 2018


Thermal barrier coatings (TBC) are critical elements of the turbomachines. On turbine blades for aircraft engines, their preparation is based on EB-PVD industrial process. Such TBCs on first generation AM1 superalloy with a beta-NiPtAl bond coating exhibit 20% of surface spallation after about 600 1h oxidation cycles at 1100°C. In this work, a new method of TBC preparation was proposed and high durability of such structures was obtained with more than 1000 1h cycles at 1100°C before 20% of spallation. More than 1400 1h cycles was even obtained with the most performing formulations. A key point was that the surface spallation was lower than 10 % after 1000 cycles for TBCs made with the 70% and 80% fiber mix (Figure 1a). In the same conditions, EB-PVD TBCs exhibit 50-80% of spallation. The preparation process relied on the addition of a high temperature binder, namely a zirconia sol, to a mix of zirconia powder and fibers. TBCs with equiaxed porosity were obtained (Figure 1b). After thermal treatments, ceramic sintering bridges between the powder, the fibers and the ceramic derived from the sol transformation formed (Figure 1c). Another benefit was obtained from the anchoring of the fibers in the thermally grown oxide (TGO), inducing a tougher TGO layer. The outstanding durability of these fibers and sol-gel matrix based thermal barrier coatings is believed to be the consequence of higher toughness of both the TBC coating and modified TGO. Indeed, crack deviations were observed in these two elements. Moreover, contrary to EB-PVD TBCs, the porosity is isotropically distributed, limiting heat diffusion towards the superalloys.

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