Insights into high thermal stability of laser additively manufactured Al₂O₃/GdAlO₃/ZrO₂ eutectic ceramics under high temperatures

Laser additive manufacturing techniques have been considered to be the most promising methods to fabricate melt-grown Al₂O₃-based eutectic ceramics which are potential candidates for high temperature structural applications. In this paper, Al₂O₃/GdAlO₃/ZrO₂ ternary eutectic ceramic was additively manufactured based on one-step melt-growth by laser directed energy deposition, and its thermal stability under high temperatures was studied. The results indicate that the as-solidified eutectic composite consists of ultrafine phases of α-Al₂O₃, GdAlO₃ and t-ZrO₂, and presents an irregular eutectic morphology with amounts of terminations and branches. The 3D-printed eutectic ceramic exhibits a superior thermal stability that no mass variation and no phase transition occur even after annealed at 1500 °C for 200 h. In addition, the submicron-scaled eutectic microstructure and the polished surface topography can maintain stability up to 1400 °C which is higher than 80% of its melting point (>0.8 T_m). With further increasing the temperature, obvious microstructure coarsening, and surface holes formation occur, leading to the severely deterioration of the mechanical property. The hardness of the as-deposited eutectic ceramic rapidly decreases from 15.84 ± 0.61 GPa to 13.01 ± 0.40 GPa after 200 h annealed at 1500 °C. The results indicate that the additively manufactured Al₂O₃-based eutectic ceramics have great potential to be long-time high-temperature structural materials applied at elevated temperatures.