Formation of carbon interphase on low electric conductive SiC fibers for SiC_f/SiC composites by electrophoretic deposition process and their mechanical properties

Abstract

Continuous silicon carbide fiber-reinforced silicon carbide (SiC_f/SiC) composites have been expected as next-generation highly reliable heat resistant materials. It is well-known that the interface between fiber and matrix acts as an important role for toughening and strengthening SiC_f/SiC composites, and it should be optimally controlled to achieve high performance SiC_f/SiC composites with excellent fracture tolerance. In this study, polypyrrole (Ppy) as an electric conductive polymer was coated on amorphous SiC fibers to increase their surface electric conductivity so that electrophoretic deposition (EPD) method can be applied to form the interphase on the SiC fibers, and carbon interphase was formed on the SiC fibers by EPD method. In addition, unidirectional SiC_f/SiC composites were fabricated by polymer impregnation and pyrolysis (PIP) process, and their mechanical properties were evaluated. Thin Ppy coating with the thickness of around 200 nm drastically increased the surface electric conductivity of the amorphous SiC fibers, and the surface of Ppy-coated SiC fibers was wholly and uniformly coated with flaky graphite particles by EPD. The average thickness of the carbon interphase formed on the Ppy-coated SiC fibers by EPD became thicker with an increase in EPD voltage, and it was revealed that the SiC_f/SiC composites with carbon interphase formed by EPD showed pseudo-ductile fracture behavior and excellent mechanical properties, and the formation of the thick carbon interphase (average thickness; 0.7 ± 0.4 µm, EPD voltage; 5 V) provided the higher bending strength and fracture energy under the experimental condition in present study. These results demonstrated that Ppy coating on the low-conductive SiC fibers was very effective to improve their surface electric conductivity, and uniform and sufficient carbon coating was successfully formed on the SiC fibers by EPD for achieving high performance SiC_f/SiC composites.