Mechanical and microwave dielectric properties of C_sf/Si ₃N₄ composites

C_sf/Si₃N₄ composites were prepared by hot-press sintering method using α-Si₃N₄ power, short chopping carbon-fiber and sintering additives. XRD analysis showed that the α-Si₃N₄ was almost completely transferred into β-Si₃N₄. The SEM micrographs of fractured surfaces showed that special network developed by rod-like β - Si₃N ₄ grains. The flexure strength of 590±10MPa, and fracture toughness of 7.94±0.1MPa·m^1/2 were achieved for the samples incorporated with 0.5wt% the carbon fibers .The microwave dielectric property of C_sf/Si₃N₄ composites was measured at a frequency range of 8.2-18GHz by E8362B PNA series network analyzer. The real part (ε′) of the permittivity of the C_Sf/Si ₃N₄ composites increases from 10 to 58 with the rise of the content of carbon fibers in the composites, as well as the imaginary part increases from 0.03 to 98 at frequency of 9.375GHz. A strong frequency dependence of the real part was observed both in X and Ku bands.