Dynamic ferroelastic domain evolution delivers outstanding high-temperature toughness in high-entropy rare-earth niobate composites

Under ultra-high temperature conditions (>1200°C), the fracture toughness of yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) declines sharply. This critical performance bottleneck severely limits their further application in high-end equipment such as aero-engine hot-end components. To address this challenge, this study systematically investigated the mechanical property evolution and associated toughening mechanisms of high-entropy rare-earth niobate composites (RE 3 NbO 7 /RENbO 4 , where RE = Dy, Ho, Er, Y, Yb) across a broad temperature range. Results indicate that fracture toughness reaches 4.2 ± 0.2 MPa m 1 / 2  at 1200°C, significantly outperforming bulk YSZ (1200°C,1–2 MPa m 1 / 2 ). Using in-situ transmission electron microscopy, this study visually captured the dynamic evolution of ferroelastic domains in the RENbO 4 phase under thermal field effects. Based on crystallographic orientation, elastic anisotropy calculations, and thermal strain distribution characteristics, a temperature-segmented toughening mechanism was established: in the low-temperature range (<400°C), fine grains and interfaces play a dominant role, achieving toughening by inducing crack deflection; in the medium-to-high-temperature range (>600°C), the evolution of ferroelastic domains becomes prominent, with ferroelastic-domain-wall migration and variant reconfiguration associated with strain accommodation within the monoclinic ac-plane; around 800°C, a ferroelastic phase transition occurs, and the domain structure gradually disappears with the phase transition. This study has developed a novel candidate heat-resistant ceramic material with excellent high-temperature mechanical properties, while also providing the theoretical basis and technical support for the design and fabrication of high-toughness ceramics for extreme environments through domain engineering control.