Ultra-low shrinkage near-net-shaping of SiC ceramics: Decoupling dimensional stability and properties via DMSO-mediated freeze-casting

Abstract

The realization of near-net-shaping in high-performance silicon carbide (SiC) ceramics is often hindered by the inherent trade-off between dimensional accuracy and structural reliability. This study aims to decouple these properties by engineering the “defect architecture” of SiC via cryoprotectant-mediated freeze-casting. High-solids-loading SiC slurries (62 vol%) were prepared with varying dimethyl sulfoxide (DMSO) contents (7-20 wt%) and the resulting casts were densified through Polymer Infiltration and Pyrolysis (PIP). We achieved an extremely low linear shrinkage of less than 1% throughout the entire process, demonstrating exceptional dimensional fidelity. Microstructural analysis revealed that DMSO addition reconfigured the ice-templated morphology by reducing the population of coarse, low-sphericity voids and promoting a more refined void distribution. This micro-architectural transformation reduced the severity of critical flaws, resulting in a three-fold increase in flexural strength (from 35.0 to 115.9 MPa) despite only minor differences in final relative density. Furthermore, the refined architecture enhanced skeletal continuity, significantly improving thermal conductivity. While conventional ceramic processing—including additive manufacturing—often suffers from drying and sintering-induced deformations that impede commercial viability, the current approach offers a viable route to bypass these challenges. Our findings demonstrate the potential of DMSO-mediated freeze-casting/PIP processing for near-net shaping of SiC ceramics, as evidenced by the ultra-low shrinkage of plate-like specimens.