Abstract: Alumina-based eutectic composite ceramics have become important candidate materials for high-temperature structural applications in high-performance aerospace engines due to their outstanding property stability, high-temperature strength, excellent oxidation resistance, and corrosion resistance. In this study, large-sized Al₂O₃/GAP/ZrO₂ eutectic ceramics with high aspect ratio and high width-to-diameter ratio were directly fabricated using laser directed energy deposition (LDED) technology with an optimized double-track overlapping scanning strategy free of sintering. The as-fabricated samples had diameters of 8-9 mm, heights of up to 135 mm, and relative densities higher than 98.5%. Under the double-track overlapping strategy, the crack density decreased progressively as the scanning speed increased from 200 to 360 mm/min, reaching a minimum value of 0.41 mm^-1 at 360 mm/min. The eutectic spacing in the colony decreased from 0.47 ± 0.07 to 0.15 ± 0.02 µm, and the irregular Chinese script eutectic structure within the colony gradually transformed into rod-like and lamellar structures. Due to the influence of local laser remelting, the cross-section of the eutectic ceramics exhibited an annular microstructure, while the longitudinal section displayed a periodically convex banded structure. At a laser power of 450 W and a scanning speed of 270 mm/min, the maximum fracture toughness of 6.35 MPa m^1/2 was achieved. The optimized scanning strategy provides a new approach for the fabrication of large-sized oxide eutectic ceramics which is expected to overcome the bottleneck in manufacturing high-quality, large-sized, and complex-shaped ultra-high-temperature oxide ceramics.

Key words: Laser directed energy deposition, Oxide eutectic ceramic, Microstructure, Mechanical property