TEM structure of (PyC/SiC)(n) multilayered interphases in SiC/SiC composites

Two generations of multilayered interphases, composed of carbon and silicon carbide, have been developed to act as a mechanical fuse in SiC/SiC compos ites with improved oxidation resistance. Pyrocarbon is an ideal interfacial material, from the mechanical point of view, whereas SiC has a good oxidat ion resistance. In the multilayered interphase, the carbon mechanical fuse is split into thin sublayers, each being protected against oxidation by the neighbouring SiC-based glass former layers. A first generation of multilay ers as synthesised by means of isobaric-CVI with sublayers with micrometric thickness. Then, in order to push forward the concept, pressure pulsed-CVI was involved to deposit nanometric scale sublayers. In this work, transmis sion electron microscopy was developed to characterise the two generations of materials. The microstructure of the layers and the influence of the fib rous preforms on the structure of the layers were studied. Examinations wer e then performed on the loaded samples and damaging mode characterised at n anometric scale. (C) 1999 Elsevier Science Ltd. All rights reserved.