Mechanical and dielectric properties of porous and wave-transparent Si₃N₄-Si₃N₄ composite ceramics fabricated by 3D printing combined with chemical vapor infiltration

Porous Si₃N₄-Si₃N₄ composite ceramics were fabricated by 3D printing combined with low-pressure chemical vapor infiltration (CVI). This technique could effectively improve the designability of porous Si₃N₄ ceramics and optimize the mechanical and dielectric properties. The effects of process parameters including the deposition time and heat treatment on the microstructure and properties of porous Si₃N₄-Si₃N₄ composite ceramics were studied. The study highlights following: When CVI processing time was increased from 0 to 12 h, the porosity decreased from 68.65% to 26.07% and the density increased from 0.99 to 2.02 g/cm³. At the same time, the dielectric constant gradually increased from 1.72 to 3.60; however, the dielectric loss always remained less than 0.01, indicating the excellent electromagnetic (EM) wave-transparent performance of porous Si₃N₄-Si₃N₄ composite ceramics. The maximum flexural strength of 47±2 MPa was achieved when the deposition time attained 6 h. After heat treatment, the porosity increased from 26.07% to 36.02% and the dielectric constant got a slight increase from 3.60 to 3.70 with the dielectric loss still maintaining lower than 0.01. It has been demonstrated that the porous Si₃N₄-Si₃N₄ composite ceramics are a promising structural and EM wave-transparent material suitable for high temperature service.