Texture control of pyrolytic carbon coatings and effects of coating thickness on the tensile properties of SiC fibers

Abstract

High-textured pyrolytic carbon (PyC) is the ideal interface for SiC fiber-reinforced SiC matrix (SiCf/SiC) composites. To prepare high-textured PyC coatings on SiC fibers efficiently, chemical vapor deposition (CVD) technique was applied with the single precursor ethanol. The effects of CVD parameters on the morphology and textures of PyC were investigated in detail. Rough laminar (RL), smooth laminar (SL) and regenerative laminar (ReL) PyC could be obtained by controlling the CVD parameters. High-textured RL PyC could be stably synthesized in a large distance range in the horizontal tube furnace at 1150 °C and 10–20 kPa (total pressure), which inferred that low temperature and negative pressure were beneficial to the formation of RL PyC. Conversely, when the temperature was up to 1350 °C, the textures of PyC at different deposition positions varied considerably. In the vicinity of isothermal zone, the texture evolution of PyC with deposition positions followed the pattern of SL→RL→SL, which could be ascribed to the ratio change of the small linear hydrocarbons (fillers) and the aromatic hydrocarbons (particles) in the gas phase. The texture evolution followed the Particle-Filler model. In addition to PyC textures, the PyC coating thickness played a critical role in regulating the mechanical properties of SiC fibers and SiCf/SiC composites. In the present work, the effects of thickness of RL PyC coatings on the tensile properties of SiC fibers were investigated. The SiC fibers with 0.3 μm RL PyC coating showed the highest average tensile strength (2735 MPa) and Weilbull modulus (10.34), which might be ascribed to the repair of fiber surface defects and the appropriate stress state between fibers and coatings. The results could provide essential data for the interface design and optimization of SiCf/SiC composites.