High toughness and CMAS resistance of REAlO3/RE2Zr2O7 (RE = La, Nd, Sm, Eu, Gd, and Dy) composites with eutectic composition for thermal barrier coatings

Although rare earth zirconates (RE2Zr2O7) have garnered 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 high service temperatures, which impedes their practical application. 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 significantly enhanced the fracture toughness by more than 40% relative to that of RE2Zr2O7 but also exhibited improved resistance to CMAS corrosion. The increase in toughness arises from multiple mechanisms, such as ferroelastic toughening, fine-grain strengthening, and residual stress toughening, all of which trigger more crack defects and energy consumption. Additionally, the CMAS penetration depth of the REAlO3/RE2Zr2O7 composites is approximately 36% lower than that of RE2Zr2O7. Al–O constituents in composites can capture CaO, SiO2, and MgO in CMAS melts and increase their viscosity, resulting in 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 those of 7–8 wt %Y2O3 partially stabilized ZrO2 (YSZ), indicating their potential as TBC materials.