Effect of crystalline Si3N4 fillers on the mechanical strength and thermal stability of complex SiCN(O) ceramic architectures produced by powder bed fusion and densified via polymer infiltration and pyrolysis

Silicon nitride is a high-performance ceramic recognized for its mechanical, thermal, and chemical stability at elevated temperatures. In this study, we present a novel method to fabricate macroporous Si₃N₄ ceramics via powder bed fusion of polyamide mixed with 0-40 vol% of crystalline Si₃N₄ powder. The printed preforms were subsequently infiltrated with a polysilazane polymer and pyrolyzed to form SiCN(O) matrices containing β-Si₃N₄ particles. A rotated cube lattice was selected as a benchmark geometry and scaled to compensate for shrinkage. The effects of ceramic filler content on densification, microstructure, strength, and oxidation resistance at 1500 °C were investigated. Increasing β-Si₃N₄ content improved the relative density, compressive strength, and thermal stability of the final ceramics. Particularly, 20–40 vol% Si₃N₄ enhanced oxidation resistance by forming a protective silica-rich surface layer and stabilizing the underlying structure. This study highlights an effective strategy to tailor the high-temperature behaviour of polymer-derived ceramics for advanced structural applications.