Reinforcing effect of carbon short fibers coated with pyrolytic carbon in ceramic matrix composites

Carbon short fibers (6000 filaments) with a length of 6 mm were uniformly coated with pyrolytic carbon (pyC) in continuous CVD process using propane-hydrogen mixture as precursor. The process conditions for the fiber coating were optimized to meet a high deposition rate at minimum soot formation in parameter screening experiments using nonporous graphite substrates. The coated fibers were characterized by SEM and Raman spectroscopy. Their reinforcing effect was investigated in composites with C/SiC matrix. As a result of fiber coating the bending strength of the composites was increased about 30% and elongation at break increased by a factor of nine. The pyC coating modifies the fiber-matrix interface preventing too strong a bonding, resulting in damage tolerant behavior of the composites.