ZrO₂ reinforced porous Si₃N₄-based ceramics with improved mechanical properties fabricated via vat photopolymerization (VPP)

Porous Si₃N₄ ceramics are widely applied in many fields owing to their excellent properties such as high electromagnetic wave permeability, oxidation resistance, and wear resistance. Besides, the vat photopolymerization (VPP) technique can fabricate porous Si₃N₄-based ceramics with complex shapes and high precision. Nevertheless, The high absorptivity and refractive index of Si₃N₄ to ultraviolet light make it difficult to form porous Si₃N₄-based ceramics with the VPP technique. In this work, the addition of ZrO₂ simultaneously improved the printability of Si₃N₄ slurries and the performance of Si₃N₄ ceramics via VPP technology. Rheological behavior and curing properties of the slurries were investigated, and the influence of ZrO₂ content on the mechanical properties of printed Si₃N₄-based ceramics was investigated systematically. The addition of ZrO₂ decreased the UV absorptivity of composite powder, thus improving the curing depth from 25.2 ± 2.6 μm to 64.8 ± 3.7 μm. XRD analysis revealed that ZrO₂ in the composite ceramics mainly exists as the phase of yttria-stabilized tetragonal zirconia (Zr_0.92Y_0.08O_1.96), which could ensure the effect of phase transformation toughening. With the increase of ZrO₂ content, flexural strength and fracture toughness of porous Si₃N₄-based ceramics exhibited a trend of increase first and then decrease. As ZrO₂ content increased to 10 wt%, the flexural strength and fracture toughness of porous Si₃N₄-based ceramics were improved from 214.7 MPa and 4.23 MPa·m^1/2 to 345.0 MPa and 5.69 MPa·m^1/2, respectively. Therefore, this work provided an important reference for the fabrication of high-performance porous Si₃N₄-based ceramic components with complex structures.