Features of Synthesizing Ceramic Composites Discretely Reinforced by Carbon Fibers and SiC Nanowires Formed in situ in the Combustion Wave

Abstract

A new method is proposed for the engineering of SiC-based ceramic-matrix composite materials strengthened by discrete carbon fibers and single-crystal silicon carbide nanowires. Depending on the macrokinetic characteristics of the combustion process, either diffusion layers, particles of silicon carbide, or silicon carbide nanowires with a diameter of 10–50 nm and a length of 15–20 μm can be formed on the surface of carbon fibers. The sequence of chemical transformations and structure formation in the combustion wave of Si–C–C2F4 and Si–C–C2F4–Ta mixtures was studied. Silicon carbide nanowires formed in the combustion wave had high crystallinity and a defect-free TaSi2/SiC interface. The misorientation of the lattices at the interface is about 6%. Nanowires are able to relax the mechanical stresses during growth via the rotation along the growth direction. The optimal combustion temperature for the growth of silicon carbide nanofibers is 1700 K at a ratio of C2F4 : C = 2. The lower temperature threshold for the growth of silicon carbide nanowires is caused by a decrease in the yield of reactive fluorides, while the upper-temperature threshold is caused by a failure of the adsorption blocking mechanism on the surface of the nanofibers and the destabilization of the TaSi2 + Si eutectic droplet. Composites with a SiC–TaSi2 ceramic matrix and a relative density of 98%, a hardness of 19 GPa, a flexural strength of 420 MPa, and fracture toughness of 12.5 MP m1/2 were obtained by hot pressing. An increase in the strength of the carbon fiber-matrix interface has manifested in the suppression of carbon fiber pull-out from the matrix.