B Sarhan ef al./ Composites: Part A 32(2001)1095-110 process did not cause any warping or cracking of the fibre and causes formation of notch-like damage on fibres composites. The thickness of the fugitive layer in the refer-(Fig. 4(a)) ence composite was significantly smaller than the carbon The gap closure at the interface of the fugitive/ZrO2- yer after hot-pressing (about 80 nm double layer composites was very advanced already after 200 nm), immediately after the oxidation of carbon layer hot-pressing but led to a complete disappearance of the gap at 1200.C/2 h. The thickness of the fugitive and ZrO at 1300C, after 1000 h of continuous heating. The Zro- layers in the fugitive/ZrO2-composites were reduced to layer showed sintering-related morphological changes, result 0 nm and 200 nm, respectively. The thickness of the ing in a rough surface development and thickness reduction fugitive layer in the fugitive/Al2O3-double layer com-(Fig 4(b)). In the fugitive/Al2O3-double layer-composites posites showed no change. The thickness variations of also sintering necks formed after 1000 h continuous heating the interphases as well as numerical mechanical data to at 1300C. However, in this case, the interaction was not the composites before and after heat-treatment are listed only between the fibre and the Al2O3-layer, but also between in Table 1 the matrix and the Al2O3-layer. So that the thickness of the Generally the fugitive layer is thermally unstable and gap was heterogeneous; larger where sintering-related ses progressively as the heat-treatment temperature and contacts between the AlO3-layer and the matrix took duration increases. This is mainly because the matrix as well place, thinner or closed where the fibre and the Al2O as the oxide layer maintains a substantial sintering activity layer were sintered together(Fig 4(c)) after hot-pressing. At the interface of the reference compo- The interfacial relations after cyclic treatment at 1300.C site between the matrix and the fibre substantial sintering differ from those under continuous heat-treatment at the necks form at 1300C after 1000 h continuous exposure in same temperature and same exposure time,(Fig. 5(a)-(c)) air. This interaction between the fibre and the matrix The fugitive layer appeared to be maintained in all compo- educes the amount of alumina on the surface zone of the sites, although to different extents in each composite. The bR m Fig. 5. Scanning electron micrographs of the interphases after 1000 thermal cycles at 1300.C in air:(a) control sample:(b) fugitive/ZrO2; and(c)fugitive/ A12O3     ,           -    &         ,           1 @)      ')) 2          8'))
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