High toughness and CMAS resistance of REAlO <sub>3</sub>/RE <sub>2</sub>Zr <sub>2</sub>O <sub>7</sub> (RE = La, Nd, Sm, Eu, Gd, and Dy) composites with eutectic composition for thermal barrier coatings
Zijian Zhang, Jian Sun, Guanghua Liu, Yi Han, Wei Liu, Yi Li, Wei Wang, Xiangyang Liu, Peng Zhang, Wei Pan, Chunlei Wan
Abstract
Although rare earth zirconates (RE<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub>) 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 REAlO<sub>3</sub>/RE<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> (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 RE<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> 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 REAlO<sub>3</sub>/RE<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> composites is approximately 36% lower than that of RE<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub>. Al–O constituents in composites can capture CaO, SiO<sub>2</sub>, and MgO in CMAS melts and increase their viscosity, resulting in enhanced CMAS corrosion resistance. The thermophysical properties of the REAlO<sub>3</sub>/RE<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> composites were also investigated, and their coefficient of thermal expansion and thermal conductivity are comparable to those of 7–8 wt %Y<sub>2</sub>O<sub>3</sub> partially stabilized ZrO<sub>2</sub> (YSZ), indicating their potential as TBC materials.