The lifetime of Si bond coats in environmental barrier coatings (EBCs) is constrained by phase transition-induced cracking at the SiO₂ scale. In this study, reactive self-consumption and lattice solid solution strategies are employed to address this limitation via Si–Yb₄Al₂O₉ composite coatings. The formation of an Yb₂Si₂O₇ layer, through the consumption of the thermally grown SiO₂ scale and Yb₄Al₂O₉, reduces the SiO₂ thickness and significantly lowers the cracking driving force. Furthermore, the incorporation of Al into the SiO₂ lattice stabilizes high-temperature β-SiO₂, preventing phase transition-induced cracking. The proposed coating demonstrated an oxidation lifetime 20 times longer than that of pure Si at 1370 °C, highlighting its potential as an EBC bond coating.

Double-layered thermal barrier coatings (DL-TBCs) have been developed to meet multiple service requirements, such as low thermal conductivity, high thermal stability, and high fracture toughness. Conventional DL-TBCs are often designed on the basis of equal total thickness to have long lifespans, which may weaken the thermal insulation. The reason is that the single-scale designed structure often has opposite effects on the thermal and mechanical properties. To enhance both the thermal insulation and lifespan, this work designed durable DL-TBCs at multiple scales under equivalent thermal insulation. The macroscopic thickness ratio of the top layer to the bottom layer was tailored to optimize the total and single thicknesses, and the microscopic pore size in the top layer was tailored to resist sintering. Six groups of samples with different thickness ratios were prepared. The thermal cycling test revealed that the lifespan of DL-TBCs first increases but then decreases with increasing thickness ratio. The optimized thickness ratio is 2:3 for DL-TBCs, which have the largest lifespan among the six groups. The cross-sectional morphologies revealed that the failure mode changed from the spallation of the top layer to the delamination of the total double layers. The long lifespan of the optimized DL-TBCs stems from the cotailored thickness ratio and porous structure in the top layer to lower the total cracking driving force.