Dendrite microstructure formation and enhanced toughness in high‐entropy REAlO3–RE2Zr2O7 eutectic oxide

Abstract In this study, complex GdAlO 3 –Gd 2 Zr 2 O 7 and high‐entropy REAlO 3 –RE 2 Zr 2 O 7 (RE = Nd, Sm, Gd, Eu, and Dy) composites with an equiaxed dendrite structure at eutectic composition are successfully fabricated using a gas levitation containerless solidification method. The unique microstructure of the composites is characterized, and the evolution process of the dendritic structure is explained. The formation of dendrites at eutectic composition is attributed to the rapid cooling induced by the shutoff of lasers and the homogeneous temperature field and nucleation achieved through gas levitation. The GdAlO 3 –Gd 2 Zr 2 O 7 and high‐entropy oxide composites exhibit enhanced fracture toughness compared to the bulk samples fabricated by solid‐state sintering methods. The fracture toughness increases by 44% for GdAlO 3 –Gd 2 Zr 2 O 7 bulk sample and 34% for high‐entropy REAlO 3 –RE 2 Zr 2 O 7 bulk sample, which can be attributed to the complicated interfaces introduced by the equiaxed dendritic microstructure and the high thermal mismatch stress between two phases. Additionally, the high‐entropy REAlO 3 –RE 2 Zr 2 O 7 oxides exhibit excellent high‐temperature stability, with no significant change in dendritic microstructure or fracture toughness even after holding at 1573 K for 100 h. These findings suggest the potential of high‐entropy eutectic oxide ceramics with dendrite microstructure for advanced engineering applications.