J. Phys. IV France 05 (1995) C5-769-C5-776
LPCVD Pyrocarbon Coating on Unidirectional Carbon Fiber Yarns : an Efficient Interphase for Aluminium Matrix CompositesP. Bertrand, M.H. Vidal-Setif and R. Mevrel
ONERA, Direction des Matériaux, BP. 72, Châtillon cedex, France
In order to optimize the interfaces in carbon fiber (high resistance Toray T800) reinforced aluminium matrix composites, a pyrolytic carbon (Cp) layer has been developed by a CVD process using a hot wall reactor operating at reduced pressure. The Cp, which has a weak shear strength, is introduced to promote adequate debonding at the fiber/matrix interface. In a first step, classical CVD studies are conducted on planar carbon substrates with a parametric investigation of the effects of temperature, pressure, reactant flow rates on the growth rate and morphology of the coating. For Cp, obtained form thermal decomposition of ethylene, a very high activation energy (310 kJ/mol) and a decrease in coating growth rate with the reactant residence time indicate that the reaction limiting step occurs in the gaseous phase. The carbon coatings exhibit a macroscopic stratified morphology which could promote internal delamination. In a second step, deposition parameters have been optimized to ensure a good infiltration of 6000 filaments yarns. Finally, the influence of carbon underlayer on the mechanical properties of coated fibers is determined by tensile tests on monofilaments and interpreted in terms of Weibull distribution. The results on aluminium composites confirm the beneficial role of mechanical fuse played by the Cp coating.
© EDP Sciences 1995