Preparation of large-size Al₂O₃/GdAlO₃/ZrO₂ ternary eutectic ceramic rod by laser directed energy deposition and its microstructure homogenization mechanism

Laser 3D printing based on melt growth has great potential in rapid preparation of Al₂O₃-based eutectic ceramics. In this work, large-scale Al₂O₃/GdAlO₃/ZrO₂ ternary eutectic ceramic rod with diameter of 4–5 mm and height higher than 250 mm was additively manufactured by laser directed energy deposition. Especially, heat treatment was applied to eliminate the microstructure heterogeneity in the as-deposited eutectic ceramic, and the microstructure homogenization mechanism was studied in depth. The results indicate that colonies and banded structures completely disappear after the heat treatment, producing a homogeneous network eutectic structure. The microstructure homogenization is revealed to experience three stages of discontinuous coarsening, continuous coarsening and microstructure coalescence. Additionally, it is found that the eutectic spacing linearly increases with the heat treatment time, meaning that the coarsening behavior of the laser 3D-printed Al₂O₃/GdAlO₃/ZrO₂ eutectic ceramic satisfies well with the Graham-Kraft model.