Laser based coating and modification of carbon fibres: application of industrial lasers to manufacturing of composite materials

For high temperature applications of fibre reinforced ceramic composites, the adhesion, and chemical reactions at the fibre-matrix interface, has to be engineered by coating the fibres. Based on a technological 5 kW cw-CO2 laser, an atmospheric pressure laser assisted CVD process has been established performing a continuous high rate coating of carbon fibre rovings. Layers of pyrolytic carbon have been deposited from CH4 with a rate of 0.6 μm/s, which enhances the tensile strength and Weibull modulus of fibres. The design of the LCVD reactor and the optimization of its operational conditions are supported by computational fluid dynamics techniques. The gas flow dynamics, concentration of species and heat tranfer in the reaction chamber have been calculated. Within the symmetrical chamber a flow regime is established with a free standing laminar gas flow around the fibre tape which shields the reaction zone against purge gases. The diffusion limited deposition rate of this configuration is estimated. The influence of laser irradiation on mechanical properties and structure of the carbon fibres have been checked by tensile (bundle) testing, SEM/EDX, XRD and Raman spectroscopy. The detected changes indicate a complex dependence on irradiation time, laser power and gaseous ambient.