Enhancing rheology and mechanical properties of DLP 3D-printed Si₃N₄ materials via composition optimization and gas-pressure sintering

Digital light processing (DLP) is a crucial additive manufacturing (AM) technique for producing high-precision ceramic components. This study aims to optimize the formulation of Si₃N₄ slurry to enhance both its performance and manufacturability in the DLP process, and investigate key factors such as particle size distribution, photopolymer resin monomer ratios, and dispersant types to improve the slurry's rheological properties. Through these optimizations, a photosensitive Si₃N₄ slurry with 50vol% solid content was developed, exhibiting excellent stability, and low viscosity (2.48 Pa·s at a shear rate of 12.8 s^–1). The effects of gas-pressure sintering on the material's phase composition, microstructure, and mechanical properties were further explored, revealing that this technique significantly increases the flexural strength of the green body from (109 ± 10.24) to (618 ± 42.15) MPa. The sintered ceramics exhibited high hardness ((16.59 ± 0.05) GPa) and improved fracture toughness ((4.45 ± 0.03) MPa·m^1/2). Crack trajectory analysis revealed that crack deflection, crack bridging, and the pull-out of rod-like β-Si₃N₄ grains,are the main toughening mechanisms, which could effectively mitigate crack propagation. Among these mechanisms, crack deflection and bridging were particularly influential, significantly enhancing the fracture toughness of the Si₃N₄ matrix. Overall, this research highlights how monomer formulation and gas-pressure sintering strengthen the performance of Si₃N₄ slurry in the DLP three-dimensional printing technique. This work is expected to provide new insights for fabricating complex Si₃N₄ ceramic components with superior mechanical properties.