A succession of two reactive chemical vapour depositions (RCVD) processes have been used to produce a double coating of TiC and SiC on a graphite substrate. In this paper, thermodynamic computations have been used to define the optimal conditions of the partial or the total conversion of a TiC coating into SiC. The experiments have been made on TiC powders and planar graphite substrates. The texture and the microstructure of the layers have been investigated as a function of the initial gas composition for different temperatures. These results will be useful to deposit a protective double layer on every single filament of a carbon fibre.