Evolution of mechanical and electromagnetic interference shielding properties of C/SiC during oxidation at 700 °C

Abstract

C/SiC is a promising structural-functional material with excellent mechanical and electromagnetic (EM) interference shielding properties. In order to investigate its evolution of mechanical and shielding properties during intermediate temperature oxidation, C/SiC composites were oxidized at 700 °C for different times in this study. The oxidation of C/SiC at 700 °C leads to the consumption of pyrocarbon (PyC) interphase and carbon fibers. As the content of PyC-coated carbon fibers decreases from 41.7 vol.% to 0 vol.%, the volume fraction of carbon fibers that can effectively load decreases. The abilities of C/SiC both in reflecting and absorbing EM waves also decrease due to the decline of electrical conductivity. Consequently, the flexural strength, fracture toughness and total shielding effectiveness of C/SiC decrease by 95.5 %, 97.4 % and 44.2 %, respectively. The decrease of mechanical properties is sensitive to the oxidation of PyC interphase. The decrease of shielding properties depends on the continuity and content of carbon fibers. The much higher retention ratio of shielding properties than mechanical properties is attributed to the high density stacking faults (SFs) in columnar SiC crystals. These SFs are formed by embedding 2H–SiC segments in 3C–SiC. Dipole polarization loss occurs at 3C–SiC/2H–SiC interfaces.