Si3N4 ceramics are promising wave-transparent materials with excellent mechanical and dielectric properties.Vat photopolymerization(VPP)three-dimensional(3D)printing provides a strategy for preparing ceramics with controllable complex structures.However,the difficulty in solidifying the slurry due to partial ultraviolet(UV)light absorption and the high refractive index of Si3N4 particles during the VPP process severely hinder the molding of Si3N4 ceramics.A higher laser power must be used to increase the curing depth,which generates large internal stresses and warps the samples.This study presents a method to solve the warpage problem during VPP-3D printing using tributyl citrate as a plasticizer.The plasticizer can weaken the force between polymer molecular chains and reduce the internal stress of the green body.Warpage decreases gradually with increasing tributyl citrate content,and the warpage decreases to 0%when the plasticizer content reaches 30 wt%at high laser powers from 600 to 750 mW.Samples with different layer thicknesses were printed,and the optimum thickness of 40μm was obtained,at which the sintered Si3N4 samples possessed a unique combination of mechanical properties,including a bending strength of 338.29±12.08 MPa and a fracture toughness of 6.94±0.11 MPa·m1/2 for the loading direction perpendicular to the build surface and 5.37±0.99 MPa·m1/2 for the loading direction parallel to the build surface.The dielectric constant of all the samples is maintained in the range of 5.462–6.414.This work is expected to guide vat photopolymerization and the preparation of complex Si3N4 ceramic components.
Highly porous Si_(3)N_(4)ceramics with unidirectionally aligned pore channels are gaining significant attention across various fields due to their outstanding functional capabilities.However,achieving high strength in such unidirectional highly porous Si_(3)N_(4)ceramics remains challenging.Herein,we design and fabricate a novel β-Si_(3)N_(4)scaffold composed of directionally aligned lamellar walls with a textured microstructure by directionally freeze casting ofα-Si_(3)N_(4)suspensions with fine elongatedβ-Si_(3)N_(4)seeds addition,followed by liquid phase sintering.During the sintering,the scaffold exhibited anisotropic shrinkage,and fibrousβ-Si_(3)N_(4)grains were synthesized through epitaxial growth on the seeds preferentially oriented or the nuclei originated fromα-Si_(3)N_(4)powders,resulting in the grains aligned parallel to lamellar walls and bridged the walls.Seed additions of 7 to 15 wt%were beneficial for the optimized distribution of the two types of β-Si_(3)N_(4)grains,which contributed to the excellent resistance to bucking-induced fracture for the walls.Compared with other unidirectional porous Si_(3)N_(4)prepared by freeze-casting in the literature,the Si_(3)N_(4)scaffold exhibited out st anding compressive strength,ranging from 2.8 to 22.0 MPa,as the porosity decreased from 94.4%to 88.0%and the density increased from 175 to 365 mg/cm^(3).The lightweight and strong Si_(3)N_(4)scaffolds are promising candidates for engineering applications in harsh environments.
Qiang ZhiShan ZhaoBaoqiang HouNanlong ZhangFeng LiBo WangJianfeng Yang
