Additive manufacturing of silicon nitride ceramics via DLP: A synergistic engineering strategy for achieving ultra-high solid loading slurries

Digital light processing (DLP) technology offers great promise for fabricating geometrically intricate silicon nitride (Si 3 N 4 ) ceramics, yet its advancement has been persistently constrained by the intrinsic challenge of formulating slurries that simultaneously enable high solid loading and low viscosity. This work presents a synergistic strategy that effectively resolves this bottleneck. Our approach integrates optimized physical packing (coarse/fine of 3:7) with precise colloidal interface engineering, employing a novel acrylate-modified block copolymer (KMT-3510) in conjunction with a short-chain dispersant (BYK-9076). Mechanistic insights reveal that the polar groups (C O and ester C O) of KMT-3510 form strong hydrogen bonds with the Si 3 N 4 surface, while its hydrophobic alkane chains (C H) extend into the resin matrix, establishing a robust steric hindrance barrier. This synergistic dispersion enabled a Si 3 N 4 slurry with a high solid loading of 60 vol% and a low viscosity of 3.10 Pa·s at 12 s −1 , demonstrating excellent rheological performance. Using this high-solid-loading slurry, fully dense ceramic parts were successfully fabricated via DLP, followed by debinding and gas-pressure sintering at 1800 °C. The sintered ceramics inherited excellent mechanical properties, including a flexural strength (742 ± 24 MPa), Vickers hardness (16.8 ± 1.6 GPa), and fracture toughness (5.02 ± 0.34 MPa·m 1/2 ). Microstructural analysis indicated that the high toughness originates from the synergistic activation of multiple toughening mechanisms, such as crack deflection, grain bridging, and β -Si 3 N 4 grain pull-out. This work provides a clear and effective slurry design pathway for the DLP-based fabrication of high-performance Si 3 N 4 ceramics with complex geometries.