Preparation of high‐strength Si 3 N 4 ceramics via vat photopolymerization: A bi‐phase particle size gradation strategy

Abstract This paper introduces an approach to preparing high‐strength Si 3 N 4 ceramics using vat photopolymerization with a bi‐phase particle size gradation strategy. The influence of different ratios of coarse β‐Si 3 N 4 powders (Cβ) and fine α‐Si 3 N 4 powders (Fα) on the slurry performance, microstructure evolution, and final ceramic strength was systematically studied. It was found that an appropriate particle size gradation can significantly reduce the viscosity of the slurry. The curing depth of Si 3 N 4 slurries decreases with increasing Fα content, while the stability increases. During sintering, dissolved Fα‐Si 3 N 4 not only directly precipitates into small elongated β‐Si 3 N 4 grains but also onto the neighboring Cβ‐Si 3 N 4 , promoting the development of large elongated β‐Si 3 N 4 grains and resulting in a bimodal microstructure distribution. The highest strength of Si 3 N 4 ceramics was achieved with a ratio of 6:4 Cβ to Fα Si 3 N 4 powders. Under these conditions, the Si 3 N 4 ceramics exhibited a flexural strength of 472 MPa, significantly higher than that of Si 3 N 4 ceramics prepared using pure Cβ/Fα powders. The strength improvement is primarily due to the well‐designed bi‐phase particle size gradation strategy, which optimizes slurry performance, minimizes defects that may be introduced during the green part printing process while controlling the microstructure evolution during sintering, achieves the ideal bimodal microstructure distribution. The outcomes of this research demonstrate the feasibility of using vat photopolymerization with bi‐phase particle size gradation for the preparation of high‐strength Si 3 N 4 ceramics, which has great potential for application in the manufacturing of various ceramic products.