Behavior of Short Carbon Fibers in C _fiber /Si ₃ N ₄ Composites by Hot Pressed Sintering

C _fiber /Si ₃ N ₄ composites were prepared by introducing short carbon fibers into a mixture of silicon nitride and sintering additives (La ₂ O ₃ —Y ₂ O ₃ ) by hot pressed sintering. The effects of fibers on microstructure and mechanical properties of composites were discussed after higher temperature sintering. The corrosion of carbon fibers was manifested in two characteristic ways: (1) the internal fiber had exfoliative structure and some serious cavities were easily found at the interfaces between Si ₃ N ₄ matrix and carbon fibers; (2) the fiber surface was covered by β-Si ₃ N ₄ crystallites. When the fiber content varied from 0 to 1 wt%, the fracture toughness increased from 6.6 MPa · m ^1/2 to 8.01 MPa· m ^1/2 . The flexural strength decreased from 638.14 MPa to 584.63 MPa with the rise of short fiber content.