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Gadolinium zirconate (GZ) has become a promising thermal barrier coating (TBC) candidate material for high-temperature applications because of its excellent high-temperature phase stability and low thermal conductivity compared to yttria-stabilized zirconia (YSZ). The double-ceramic-layered (DCL) coating comprised of GZ and YSZ was confirmed to possess better durability. However, the particle-erosion resistance of GZ is poor due to its low fracture toughness. In this study, a novel erosion-resistant layer, an Al₂O₃-GdAlO₃ (AGAP) amorphous layer, was deposited as the top layer to resist erosion. Three triple-ceramic-layer (TCL) coatings comprised of an Al₂O₃-GAP layer as the top layer, a GZ layer, a GZ/YSZ composite layer, and a rare-earth-doped gadolinium zirconate (GSZC) layer as the intermediate layer, and a YSZ layer as the base layer. For comparison, an AGAP-YSZ DCL coating without a middle layer was prepared as well. Under the erosion speed of 200 m/s, only a small amount of spallation occurred on the surface of the Al₂O₃-GAP layer, indicating a superior particle-erosion resistance. In the thermal shock test, the Al₂O₃-GAP layer experienced glass transition and the glass transition temperature was close to 1500 °C. The hardness of the Al₂O₃-GAP coating after glass transition increased ~170% compared to the as-sprayed Al₂O₃-GAP coating. Moreover, The DCL TBC and TCL TBCs exhibited different failure mechanisms, which illustrated the necessity of the middle layer. The finite element model (FEM) simulation also shows that the introduction of the GZ layer can obviously reduce the thermal stress at the TC/BC interface. In terms of coating with a modified GZ layer, the AGAP-GZ/YSZ-YSZ coating and AGAP-GSZC-YSZ coating showed a similar failure model to the AGAP-GZ-YSZ coating, and the AGAP-GSZC-YSZ coating exhibited better thermal shock resistance. Full article

A novel Al₂O₃-GdAlO₃ (GAP) amorphous ceramic coating was in situ prepared via atmospheric plasma spraying (APS). The Al₂O₃/Gd₂O₃ sprayable powders possessed excellent sphericity and fluidity after heat treatment at 1173 K without solid-phase reaction, which indicated that the Al₂O₃-GAP coating deposition process was significantly simplified. The Al₂O₃-GAP amorphous coating showed high glass transition temperature (1155.1 K), initial crystallization temperature (1179.2 K), local activation energy (847.6 kJ/mol) and nucleation resistance (88.3). Compared with almost all amorphous materials, the Al₂O₃-GAP amorphous coating possessed greater crystallization activation energy, which was conducive to its high-temperature microstructure stability. Furthermore, the hardness and elastic modulus of Al₂O₃-GAP coating fluctuated with a tiny range when increasing the nanoindentation depth from 500 nm to 2000 nm, which exhibited excellent uniformity of microstructure and mechanical performance of the coating. Therefore, the results showed that the Al₂O₃-GAP amorphous coating had a better potential for large-scale engineering application under harsh service conditions. Full article