LDED-induced pore defects in Al₂O₃/GdAlO₃/ZrO₂ eutectic ceramics: Influence of specimen geometry on pore evolution mechanism

The preparation of large-sized complex melt-grown oxide eutectic ceramics using laser directed energy deposition (LDED) has excellent development potential. There is an urgent need for an in-depth study of pore evolution mechanisms to improve forming quality and mechanical properties. In this study, eutectic ceramics with different geometries were directly prepared based on melt-growth by LDED, such as rod-shaped, wall-shaped, and right-angle wall. The influencing factors of pore defects were studied, and the correlation between pore evolution mechanism and specimen geometry was discussed. The high dissolved oxygen content induced the molten pool convection pattern to change from outflow to inflow, resulting in pore aggregation in the surface layer of the rod-shaped specimens. The laser beam movement brought additional bubbles to the end regions with a higher solidification rate and larger floating distance, which led to pore defects accumulating at both ends of the wall-shaped eutectic ceramics. The viscous force of high-viscosity ceramic melt dominated the movement of bubbles from inside to outside at the corner of the right-angle wall, which promoted pores concentrated on the outside of the inflection point. Consequently, the size and shape of eutectic ceramics, the melt viscosity, and the molten pool convection pattern all affected the formation and distribution of pore defects. This paper clarifies the pore evolution mechanism in oxide ceramics with different geometric shapes, which has specific guiding significance for LDED-fabricated large-scale, complex ceramic samples.