Preparation of high-strength Si3N4 ceramics via vat photopolymerization: A bi-phase particle size gradation strategy

Abstract

This paper introduces an approach to preparing high-strength Si₃N₄ ceramics using vat photopolymerization with a bi-phase particle size gradation strategy. The influence of different ratios of coarse β-Si₃N₄ powders (Cβ) and fine α-Si₃N₄ 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 Si₃N₄ slurries decreases with increasing Fα content, while the stability increases. During sintering, dissolved Fα-Si₃N₄ not only directly precipitates into small elongated β-Si₃N₄ grains but also onto the neighboring Cβ-Si₃N₄, promoting the development of large elongated β-Si₃N₄ grains and resulting in a bimodal microstructure distribution. The highest strength of Si₃N₄ ceramics was achieved with a ratio of 6:4 Cβ to Fα Si₃N₄ powders. Under these conditions, the Si₃N₄ ceramics exhibited a flexural strength of 472 MPa, significantly higher than that of Si₃N₄ 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 Si₃N₄ ceramics, which has great potential for application in the manufacturing of various ceramic products.