One-step preparation of melt-grown Al₂O₃/GdAlO₃/ZrO₂ eutectic ceramics with large size and irregular shape by directed energy deposition

Directed energy deposition (DED) has become a promising technique to directly prepare high-performance Al₂O₃-based eutectic ceramics without sintering due to its unique advantage in one-step fabricating of highly dense parts with large sample size and complex shape. However, due to the cyclic scanning, and local rapid melting and cooling of the DED process as well as the intrinsic hard and brittle characteristic of ceramic, the study on preparation of ceramic material by DED is still in its infancy. The defect control and growth process optimization are still the research focuses in this field. In this paper, ultra-high temperature Al₂O₃/GdAlO₃/ZrO₂ ternary eutectic ceramics with different shapes were additively manufactured by DED, and the formation, evolution, and elimination of cracks during the fabrication process were investigated. It is found that the cracks can be divided into two types of transverse cracks and longitudinal cracks, and the influence of longitudinal crack on the forming quality of the ceramic specimen is dominant due to the stress distribution and the longitudinal extended eutectic colony structure. The formation of cracks can be effectively suppressed through shortening the scanning vector length less than 5 mm. In addition, a theoretical criterion for layer-wised stable forming of eutectic ceramics is established on the basis of the crack control. By co-controlling the scanning length and scanning speed to maintain the monolayer processing time is 1.25 s, large size eutectic ceramic rod with sample height > 410 mm is stably prepared that the sample height linearly increases with the number of deposited layers. In addition, corner-shaped eutectic ceramics are also one-step prepared through changing the scanning strategy. The as-obtained results can lay a theoretical and technical foundation for laser additive manufacturing and solidification defect control of high-performance oxide eutectic ceramics with large size and complex shapes.