Green parts with complex structures were successfully fabricated from preceramic polymer/photosensitive resin slurries containing inert fillers (Si₃N₄ whiskers) by using digital light processing (DLP) 3D-printing technique. After pyrolysis, the green parts were transformed into polymer-derived ceramic matrix composites, their morphology and structure intact were retained. The introduction of the ceramic fillers not only prevented the collapse of the green parts during pyrolysis, but also effectively reduced the linear shrinkage and weight loss of the ceramic materials. Also, as a reinforcing phase, it significantly improved mechanical properties of the final composites. When the mass fraction of filler content was 10 wt.%, the bending strength of the composites could reach (160.9 ± 19.7) MPa. In addition, the effects of filler content on the microstructure and porosity of the composites were discussed. It was found that excessive filler would lead to an increase in porosity and a decrease in matrix continuity, resulting in a decrease in mechanical properties of the composites.

Si₃N₄ ceramics have great application prospects in the fields of heat dissipation and packaging of electronic components, because of their excellent chemical stability, mechanical and thermal properties. In order to prepare Si₃N₄ ceramics with excellent bending strength and thermal conductivity, Y₃Si₂C₂-MgO binary composite sintering additive was used in this work. The effects of Y₃Si₂C₂ content and high temperature soaking time on relative density, mechanical properties and thermal conductivity of Si₃N₄ ceramics were systematically studied. The optimization mechanisms of mechanical/thermal properties of the Si₃N₄ ceramics were explained based on their microstructure and phase composition analyses. Thermal conductivity and bending strength of the Si₃N₄ ceramics, prepared after high temperature soaking for 4 h and 12 h, increased first and then decreased with increasing content of Y₃Si₂C₂. The bending strength of the Si₃N₄ ceramics prepared by high temperature soaking for time for 4 h is mainly dependent on relative density, while that of the Si₃N₄ ceramics prepared by high temperature soaking for time for 12 h is related to the microstructure uniformity and Si₃N₄ grain size. The prolonging of holding time is conducive to eliminating pores and increasing grain size, resulting in enhanced densification and increased thermal conductivity. Si₃N₄ ceramics, with relative density of 99.0%, thermal conductivity of (106.80±2.64) W·m^-1·K^-1 and bending strength of (590.21±25.69) MPa, were prepared by using gas pressure sintering, at 1900 ℃ for 12 h, with the addition of 1.5 mol % Y₃Si₂C₂. Such Si₃N₄ ceramics has excellent comprehensive mechanical/thermal properties, which is conducive to improving the service safety and reliability of Si₃N₄ ceramic packaged electronic components.

In this study, the chemical precipitation coating (CP) process was creatively integrated with DLP-stereolithography based 3D printing for refining and homogenizing the microstructure of 3D printed Al₂O₃ ceramic. Based on this novel approach, Al₂O₃ powder was coated with a homogeneous layer of amorphous Y₂O₃, with the coated Al₂O₃ powder found to make the microstructure of 3D printed Al₂O₃ ceramic more uniform and refined, as compared with the conventional mechanical mixing (MM) of Al₂O₃ and Y₂O₃ powders. The grain size of Al₂O₃ in Sample CP is 64.44% and 51.43% lower than those in the monolithic Al₂O₃ ceramic and Sample MM, respectively. Sample CP has the highest flexural strength of 455.37±32.17 MPa, which is 14.85% and 25.45% higher than those of Samples MM and AL, respectively; also Sample CP has the highest Weibull modulus of 16.88 among the three kinds of samples. Moreover, the fine grained Sample CP has a close thermal conductivity to the coarse grained Sample MM because of the changes in morphology of Y₃Al₅O₁₂ phase from semi-connected (Sample MM) to isolated (Sample CP). Finally, specially designed fin-type Al₂O₃ ceramic heat sinks were successfully fabricated via the novel integrated process, which has been proven to be an effective method for fabricating complex-shaped Al₂O₃ ceramic components with enhanced flexural strength and reliability.