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

• Published in: Russian journal of non-ferrous metals 2020-09, Vol.61 (5), p.559-570
• Main Authors: Vorotilo, S., Levashov, E. A., Potanin, A. Yu, Loginov, P. A., Shvyndina, N. V.
• Format: Article
• Language: English
• Subjects: Carbon fibers; Ceramic; Ceramic fibers; Ceramic matrix composites; Ceramics; Chemistry and Materials Science; Combustion temperature; Composite Materials; Destabilization; Diffusion layers; Fiber pullout; Fiber-matrix interfaces; Flexural strength; Fluorides; Fracture toughness; Hot pressing; Lattices; Materials Science; Metallic Materials; Misalignment; Nanofibers; Nanowires; Refractory; Silicon carbide; Single crystals
• ISSN: 1067-8212; 1934-970X
• DOI: 10.3103/S1067821220050168

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–C 2 F 4 and Si–C–C 2 F 4 –Ta mixtures was studied. Silicon carbide nanowires formed in the combustion wave had high crystallinity and a defect-free TaSi 2 /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 C 2 F 4 : 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 TaSi 2 + Si eutectic droplet. Composites with a SiC–TaSi 2 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 m 1/2 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.