HREM IDENTIFICATION OF ONE-DIMENSIONALLY-DISORDERED POLYTYPES IN THE SIC (CVI) MATRIX OF SIC SIC COMPOSITES

The matrix of SiC/SiC composites has been observed by electron energy loss spectroscopy (EELS) and high resolution electron microscopy (HREM) from both the chemical and the structural point of view. In this material, columnar growth and radial arrangement around the fibres of the reinforcement are typically observed for the crystal of the matrix. The ratio, Si/C = 1, of these crystals has been checked. The cubic structure of some of them has been identified through their diffraction patterns. High resolution experiments were performed to recognize the structure of the others polytypes, which are characterized by a disorder in the direction of the tetrahedral layer stacking. For this reason, they are called, "one-dimensionally-disordered" polytypes. The PHILIPS CM30-ST point resolution (0.19 nm) enables the projected SiC structure to be recognized so that the degree of disorder in this polytype can be estimated. The interpretation of the experimental images was based on comparison with simulations.