Densified porous billets and process.

摘要

A densified porous billet is formed by depositing a matrix composition in the pores of a porous preform. The composition of the matrix is graded, varying with distance from the substrate surface. In one embodiment, pores 46 formed by the voids in a preform of three-dimensionally woven carbon fibres 42 are filled by chemical vapour deposition of a first layer 61 of carbon and subsequent layers 63, 65 of a carbon/silicon carbide composition and a final layer 67 of 100% silicon carbide to provide a step-wise gradation from carbon to silicon carbide. <IMAGE>