High toughness and CMAS resistance of REAlO ₃/RE ₂Zr ₂O ₇ (RE = La, Nd, Sm, Eu, Gd, and Dy) composites with eutectic composition for thermal barrier coatings

Although rare earth zirconates (RE₂Zr₂O₇) are garnering attention as viable candidates for thermal barrier coatings (TBCs), they suffer from low fracture toughness and accelerated calcium–magnesium–alumina–silicate (CMAS) melt corrosion at higher service temperatures, which impede their practical applications. In this work, we developed a series of REAlO₃/RE₂Zr₂O₇ (RE=La, Nd, Sm, Eu, Gd, and Dy) composites with a eutectic composition that not only show a significant enhancement in fracture toughness, over a 40% increase relative to RE₂Zr₂O₇, but also exhibit improved resistance to CMAS corrosion. The enhancement of toughness arises from multiple mechanisms such as ferroelastic toughening, fine-grain strengthening, and residual stress toughening, all of which trigger more crack defections and energy consumption. Additionally, the CMAS penetration depth of REAlO₃/RE₂Zr₂O₇ composites is approximately 36% lower than that of RE₂Zr₂O₇. Al-O constituents in composites can capture CaO, SiO₂, and MgO in CMAS melt and increase its viscosity, resulting in the enhanced CMAS corrosion resistance. The thermophysical properties of the REAlO₃/RE₂Zr₂O₇ composites were also investigated, and their coefficient of thermal expansion and thermal conductivity are comparable to YSZ, indicating the potential as TBC materials.