Combustion synthesis of SiC-based ceramics reinforced by discrete carbon fibers with in situ grown SiC nanowires

This study proposes a combustion-based ceramic matrix composite processing technique intended on single-step in situ deposition of single-crystal SiC nanowires (SiCnw) on the surface of carbon fibers (C-f) and formation of SiCnw-reinforced SiC matrix. This was accomplished by Ta-catalyzed combustion of poly-(C2F4)-containing reactive mixtures with pre-mixed chopped Cf. Depending on the combustion conditions, carbon fiber surface is subjected either to formation of diffusion layers, ceramic particle incrustation or growth of continuous arrays of carbon-coated single-crystal SiCnw with a nearly defect-free lattice, 10-50 nm diameter and 15-20 mu m length. Thermodynamics, phase and structure formation mechanisms are explored, and the optimal conditions are outlined for reproducible C-f/in situ SiCnw dual reinforcement of SiC-based ceramics. Hot pressing at 1500 degrees C produced C-f/in situ SiCnw-reinforced ceramic SiC-TaSi2 specimens with a relative density of 97%, 19 GPa Vickers hardness, 3-point flexural strength sigma = 420 +/- 70 MPa and fracture toughness K-1C = 12.5 MPa m(1/2).