Thermal resistant, mechanical and electrical properties of a novel ultrahigh-content randomly-oriented CNTs reinforced SiC matrix composite-sheet

Development of a thermal resistant CNT based sheet is important for high temperature engineering perspectives with multifunctional purposes. This work reports a novel CNT reinforced SiC matrix composite-sheet by polymer derived ceramics (PDC) processes using polycarbosilane as SiC precursor. The microstructure contains the amorphous SiC matrix (4 phases: SiC, SiCxOy, SiO2 and free carbon), the chemical sharp CNT/SiC interfaces and the ultrahigh density multi-walled CNTs that are randomly oriented. The composite-sheet is thermally and mechanically stable in non-oxidizing atmosphere up to 1000 °C. The mechanical properties of the composite-sheet are significantly enhanced, with the Young's modulus increased by ∼7 times, and the tensile strength ∼4 times, compared to those of pure CNT sheet. The strengthening mechanism is a bridging effect of the SiC matrix to the CNTs to favor better load transfers during fracturing. Therefore, the composite-sheet shows an elastic-brittle fracture response, with limited CNT pull-out in the fracture surface after tensile test. Finally, the composite-sheet shows an excellent electrical conductivity that is also comparable to the pure CNT sheet, and is found enhanced after post heat-treatment at temperatures >800 °C in non-oxidizing atmosphere, presumably due to the more content free carbon formations in the SiC matrix.