Enhanced thermal shock resistance of gradient high-entropy (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Ce2O7/YSZ thermal barrier coatings

High-entropy (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Ce2O7 (LECO) has been verified as a potential candidate for thermal barrier coatings (TBCs). In this work, two different structured LECO coatings were constructed and the thermal shock behavior was systematically investigated. In the classical double-layered LECO coating (D-LECO), the cracks initially originated from the edge and completely exfoliated from substrate after failure. To strengthen the thermal stress resistance of the coating, a gradient multilayered LECO/YSZ coating (M-LECO) was designed with five ceramic sub-layers. The thermal shock life of M-LECO was greatly enhanced by approximately 4 times. Unlike the typical TBCs, the delamination first appeared at an annular region on the surface, located away from the center and edge. Besides, the spalling only occurred in the topmost LECO layer with a thickness loss of less than 5%. After failure, the underneath coating could still provide efficient thermal protection to substrate. The better thermal shock resistance of M-LECO was mainly attributed to the fine gradient structure of the coating and the intrinsic property of high-entropy LECO. The microhardness and fracture toughness in M-LECO were strengthened layer by layer along the thickness direction, alleviating the thermal stress accumulation in the coating and greatly improving the cracking resistance of the interface. Moreover, the high-entropy effect and sluggish diffusion effect of LECO improved its sintering resistance, thereby enhancing the thermal shock resistance of M-LECO. Such design not only fully utilizes the unique thermo-physical properties of high-entropy ceramics, but also effectively solves the problem of weak adhesion between the LECO and the substrate during thermal shock.