Microstructure, thermal and mechanical properties, and thermal cycling behavior of high-entropy (Y_0.2Gd_0.2Er_0.2Yb_0.2Lu_0.2)₂Zr₂O₇/YSZ thermal barrier coatings

In this study, high-entropy rare-earth zirconate (HE-REZ) powder with the composition (Y₀.₂Gd₀.₂Er₀.₂Yb₀.₂Lu₀.₂)₂Zr₂O₇ was synthesized via a solid-state reaction method. Subsequently, HE-REZ/YSZ double-ceramic-layer (DCL) thermal barrier coatings (TBC) were fabricated using atmospheric plasma spraying (APS). The phase composition and thermal conductivity of the coatings were characterized, along with the coefficient of thermal expansion (CTE) and mechanical properties of the corresponding bulk specimens. Thermal cycling performance was evaluated through both furnace cycling and burner rig thermal shock tests. The results indicate that both the HE-REZ powder and the resulting coatings exhibit a single-phase defect-fluorite structure. The HE-REZ coating achieved a thermal conductivity of 0.72 W m⁻¹·K⁻¹ at 1400 °C, corresponding to a reduction of over 60 % compared to that of YSZ. Although the CTE of the HE-REZ bulk is slightly lower than that of YSZ, thermal cycling tests revealed that coating failure is initiated by transverse cracks propagating through the HE-REZ layer, primarily due to its significantly lower fracture toughness—about 25 % of that of YSZ.