Impact of Sintering Aid Type and Content on the Mechanical Properties of Digital Light Processing 3D-Printed Si3N4 Ceramics

Digital light processing (DLP) 3D-printed Si₃N₄ ceramics, known for their exceptional performance, offer distinct advantages in meeting the high-strength and complex structural demands of industries such as aerospace, semiconductors, healthcare, automotive, energy, and machinery. However, due to Si₃N₄’s strong chemical stability, low diffusion rate, low self-sintering ability, and high melting point, achieving densification under conventional sintering conditions is challenging. As a result, sintering additives are essential to promote the sintering process, lower the sintering temperature, improve densification, and enhance performance. In this study, 45 vol% Si₃N₄ slurries were prepared using DLP 3D printing technology, incorporating nine different combinations of sintering additives, including aluminum oxide (Al2O3), yttrium oxide (Y2O3), and aluminum nitride (AlN), in various ratios with Si3N4. The slurries were then sintered at 1800 °C for 2 h under a 1 MPa N2 atmosphere. Additionally, the phase composition, microstructure, grain distribution, and crack propagation of the materials. The results showed that a Si3N4 to Al2O3 and Y2O3 ratio of 95:2.5:2.5 produced elongated β-Si3N4 grain structures and enhanced density, achieving a maximum Vickers hardness of 12.88 ± 0.52 GPa. Additionally, the synergistic toughening effect of the rod-like β-Si3N4 grains and sintering aids significantly improved the fracture toughness of the Si3N4 ceramic matrix, with a flexural strength of 540.63 ± 10.05 MPa and a fracture toughness of 4.92 ± 0.07 MPa·m1/2. This study lays the foundation for the future application of 3D-printed Si3N4 ceramics, optimization of sintering aid combinations at different ratios, and performance enhancement in extreme environments.