EFFECT OF COUPLING TREATMENT OF CARBON-FIBER SURFACE ON MECHANICAL-PROPERTIES OF CARBON-FIBER-REINFORCED CARBON COMPOSITES

Unidirectional carbon fiber reinforced carbon composites (C/C composit es) were Prepared from a high modulus-type carbon fiber, treated with either silane or titanate coupling agents, and a furanic resin matrix precursor. Regardless of coupling treatments of fibers, a preferential ly oriented region parallel to the fiber surface was observed at the i nterphase in the carbon matrix derived from furanic resin. The matrix interphase was flattened by development of graphitic structure after h eat treatment at 2600 degrees C. In the composite fabricated from untr eated fiber, the strong adhesion between fiber and matrix resulted in damage of the reinforcing fibers by the flattening of the matrix. The coupling treatments weakened the interfacial adhesion between carbon f iber and carbon matrix, and prevented fiber damage resulting from matr ix flattening by separation at the interface. In the graphitized compo site fabricated from silane coupling-treated fibers, the interfacial a dhesion became so weak that fiber pull out was observed on fracture. T he titanate coupling treatment limited the extent of graphitization of matrix in the composite. For composites fabricated from titanate coup ling-treated fiber, the tensile strength increased with increasing hea t treatment temperature. The graphitized composites from titanate coup ling-treated fibers showed 50% higher strength than the composite from untreated fibers. (C) 1998 Published by Elsevier Science Ltd. All rig hts reserved.