Matching design of porous microstructures for double-layered thermal barrier coatings composed of Gd₂Zr₂O₇ and yttria-stabilized zirconia enables long protection

Double-ceramic-layered thermal barrier coatings (DCL-TBCs) find their way at high temperatures by a combination of phase-stable materials with cracking-resistant materials. A key for the DCL-TBCs is to work as an intact unit for the two layers all over their life span. Given that, this work tailored the porous microstructures of Gd₂Zr₂O₇ (GZO) top layer to match the bottom layer of yttria-stabilized zirconia (YSZ) to avoid interfacial cracking. Results show that the life span was extended firstly, but then was shortened with increase in spraying distance. A matching GZO-YSZ DCL-TBCs can be obtained with 66 % increase in life span when the differential degrees in porosity and 2D pore density between two layers maintained at 30 % ± 3 % and 2.0 % ± 0.2 %. Moreover, the matching GZO-YSZ DCL-TBCs exhibited a failure pattern of delamination of double layers, suggesting that the double layers worked as an intact unit. At this condition, simulation results showed that the sintering of ceramic layers and oxidation of bond coat co-play dominant roles on cracking behavior, and more porous structure can resist sintering degree to release some stress. In brief, the matching design for GZO-YSZ DCL-TBCs is expected to obtain long protection by avoid spallation of top layers.