Eutectic ceramics with exceptional hardness, elevated Young's modulus, and impressive fracture toughness have become indispensable materials for various demanding industrial applications in extreme environments. In this work, In-situ synthesis of high-entropy Al₂O₃/ (Y_0.2Eu_0.2Er_0.2Yb_0.2Lu_0.2)₃Al₅O₁₂/ ZrO₂ ceramic is successfully achieved with one-step slurry-based laser powder bed fusion (LPBF). The phase formation, microstructure morphologies, phase distribution, crystallographic characteristics, and mechanical properties are systematically investigated. The typical microstructure of a shell-core architecture resembling cellular-like features consists of both crystalline and amorphous phases. The selective aggregation of constituents is the combined outcome of solute exclusion and convective transport mechanisms. The possible presence of crystallographic orientation relationships inside the shell is: ZrO₂ // RE₃Al₅O₁₂; RE₃Al₅O₁₂ // ZrO₂. During the rapid cooling of LPBF, the amorphous phase is an intermediate metastable product of crystal structure adjustment (REAlO₃, RE₄Al₂O₉ → amorphous phase → RE₃Al₅O₁₂). Due to the slower diffusion rate and higher transition energy threshold of Eu elements, more Eu elements are retained in the amorphous phase. Structural analysis indicates that the remarkable mechanical properties can be attributed to several factors, including the significant dissociation energy, strong cationic field, stress transfer among Al₂O₃, RE₃Al₅O₁₂, ZrO₂, and the amorphous phase. Additionally, cocktail effect and the plastic deformation mechanism of the high-entropy shell contribute to these properties.

The powder bed selective laser process (sintering/melting) has revolutionised many industries, including aerospace and biomedicine. However, PBSLP of ceramic remains a formidable challenge. Here, we present a unique slurry-based approach for fabricating high-strength ceramic components instead of traditional PBSLP. A special PBSLP platform capable of 1000 °C pre-heating was designed for this purpose. In this paper, PBSLP of Al₂O₃ was accomplished at different SiC loads up to 20 wt%. Several specimens on different laser powers (120 W to 225 W) were printed. When the SiC content was 10 wt% or more, the chemical interaction made it difficult to process. Severe melt pool disturbances led to poor sintering and melting. The structural analysis revealed that the micro-structure was significantly affected by the weight fraction of SiC. Interestingly, when the content was less than 2 wt%, it showed significant improvement in the microstructure during PBSLP and no effects of LPS or chemical interaction. Particularly, a crack pinning effect could be clearly seen at 0.5 wt%.