Laser CVD vs. Hot Wall CVD : Coating of Fibres for Ceramic Composites

Abstract
Based on a technological 5 kW cw-CO₂ laser, an atmospheric pressure laser assisted CVD process has been established which performs 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. In another variant, pyro-C layers have been deposited in a technological thermal hot-wall CVD reactor on fabrics and on preforms. The layer thickness is uniform over the cross section of the fibre bundles, but variations in flow direction have been detected. Composite materials with SiC matrix have been processed by both liquid precursor infiltration using Si-polymers and by converting a carboneous matrix being infiltrated with liquid silicon. Preforms with uncoated and coated fibres have been infiltrated. The resulting composites are characterized by high tensile strength and crack resistance due to the favourable pull-out behaviour of coated fibres.