Effects of ceramic powder coating treatment on the curing behavior, mechanical properties, and microstructure of 3D printed silicon nitride ceramics

Silicon nitride (Si3N4) powder possesses a high refractive index and a significant ultraviolet (UV) absorptivity, consequently enabling great challenges in the fabrication of Si3N4 ceramics using vat photopolymerization. The TEM, SEM, XRD and XPS results indicate that the yttrium aluminum garnet (YAG) can be coated on the surface of Si3N4 ceramic powder using a non-aqueous chemical precipitation coating (NCP) process, and the effects of ceramic powder coating treatment on the curing behavior, rheological of Si3N4 slurry, and the microstructure and mechanical properties of Si3N4 ceramics were systematically investigated in this work, based on the detailed performance comparisons between the Si3N4 samples manufactured using the NCP and traditional wet ball-milling (WBM) methods, respectively. Results demonstrated that the uniform distribution of YAG film on the surface of Si3N4 powder notably can favor the enhancement of the rheological and curing behaviors of Si3N4 ceramic slurries. The viscosity of NCP ceramic slurry was observed to be 42.25 % lower than that of WBM ceramic slurry at a shear rate of 35 s(-1). Additionally, the cure depth of NCP ceramic slurry with the solid loading of 30 vol% at the exposure energy of 159.6 mJ/cm(2) was measured to be 35.4 mu m, which is 22.49 % higher than that of the WBM ceramic slurry. Moreover, compared with the WBM ceramic slurry at the same curing depth, the NCP ceramic slurry demonstrates higher precision in shaping dimensions. The bending strength and Weibull modulus of NCP-SN sample were 833.74 +/- 39.35 MPa and 25.15, respectively, which were 17.64 % and 173.07 % higher than those of WBM-SN sample. This improvement is attributed to the advantageous aspects of the NCP process, which promote the uniform distribution of the liquid phase, facilitate the sintering densification of Si3N4 ceramic, and accelerate the formation of elongated crystalline grains. Ultimately, superior-quality Si3N4 components with distinct contours were successfully fabricated. The methodology proposed in this work contributes to advancing the rapid manufacturing and performance optimization of the intricately structured Si3N4 ceramic components.