CARBON-CARBON COMPOSITES PREPARED BY A RAPID DENSIFICATION PROCESS II- STRUCTURAL AND TEXTURAL CHARACTERIZATIONS

In Part I of the present study it was shown that all carbon preforms a re suitably densified by a rough laminar pyrocarbon in the processing range 900-1200 degrees C. The composites, studied by X-ray diffraction , optical microscopy and mainly by transmission electron microscopy, a re homogeneous in porosity and textures (at micrometric and nanometric scales). The deposit is highly graphitizable ((d) over bar(002) = 0.3 36 nm and L-c > 150 nm). At a densification temperature above 1200 deg rees C, the composites are heterogeneous: an increasing textural disor der occurs in the pyrocarbon and the ability to graphitize decreases. At any processing temperature, the roughness of the substrate is a lea ding parameter. Wavy surfaces (felt) of large period generate growth c ones whereas nanometric scale roughness (T 300 type) locally disturb t he pyrocarbon preferred orientation. However, accessible protruding ar omatic layers on the fiber surface increase adhesion with the pyrocarb on. Smooth fiber surface (AS4) favors decohesions. (C) 1997 Elsevier S cience Ltd.