3.2. Nanostructure of the Sic-sublayers The first Sic sublayer was observed to be often dis- continuous, particularly when its thickness was low (i.e. The Sic present in the multilayered(PyC/SiC)n inter- 0.1 um), as shown in Fig. 2. As a result, "mechanical phase was always deposited onto pyrocarbon surfaces, bridges"were formed under such conditions, between the roughly flat, as supported by a comparison of the pyr- sublayers(inset in Fig. 2). Obviously, an optimising of the ocarbon C(002) lattice fringes TEM images (recorded at nucleation/growth processes should be further carried out about the same magnification) shown in Figs. 3 and 4. Fig. in order to achieve thinner and smoother sublayer 4 shows that there is probably e relation between the orientation of the carbon aromatic planes in the substrate 3.3. Multiple interfacing and that of the crystals in the Sic-deposit. Meanwhile, no precise relationship was found for the preferred growth The number of interfaces in the(PyC/SiC)n multi directions of SiC (i.e. 1 ll for the cubic B modification and layered interphase increases as n is raised: up to 8 when 00. 1 for the hexagonal a modification)with respect to the n=4(materials G, H, K and L)remembering that the C aromatic planes in the substrate. silicon carbide in the last sequence is the matrix itself SiC in the deposits was well crystallised, the size of the As discussed in a previous paper, the first interface has crystals being often limited by the thickness of the Sic a unique role in controlling the behaviour of the whole sublayer itself. The crystals are either of the cubic(3C)B interfacial sequence: fibre/Pyc, delle ng has to be modification or consisted of a sequence of disordered strong in order to allow multiple deflection at the dif polytypes, as shown in Fig. 5 and already reported by ferent other interfaces. Fibre surface bonding strength several authors.24. 25 The diffraction pattern(inset in Fig is related to the surface state of the fibre. In addition to 5)shows a straining of the reciprocal nodes along the the first interface(fibre/Py Ci) there exists two kinds of [lll] growth axis, i.e. perpendicular to the stacking interface characterised by a very different roughness fault plane henomena) in such multilayered(PyC/SiC)n inter The interface related to a Sic-deposit onto a Pyc c layer(e.g. PyCn-I/SiCn) was usually smooth, as already 00,2 mentioned, owing to the layered structure of pyr carbon and to its "covering capability"(tending to SIC t co0. 2 5c11 SiCAl 5n Fig. 5. Structure of the Sic-based sublayer. Inset: electron diffraction Fig 4. Growth of SiC on the surface of PyC layer: smoothness of the pattern centered on the contrasted crystal exhibiting one-dimensional3.2. Nanostructure of the SiC-sublayers The SiC present in the multilayered (PyC/SiC)n inter￾phase was always deposited onto pyrocarbon surfaces, roughly ¯at, as supported by a comparison of the pyr￾ocarbon C(002) lattice fringes TEM images (recorded at about the same magni®cation) shown in Figs. 3 and 4. Fig. 4 shows that there is probably some relation between the orientation of the carbon aromatic planes in the substrate and that of the crystals in the SiC-deposit. Meanwhile, no precise relationship was found for the preferred growth directions of SiC (i.e. 111 for the cubic  modi®cation and 00.1 for the hexagonal  modi®cation) with respect to the C aromatic planes in the substrate. SiC in the deposits was well crystallised, the size of the crystals being often limited by the thickness of the SiC sublayer itself. The crystals are either of the cubic (3C)  modi®cation or consisted of a sequence of disordered polytypes, as shown in Fig. 5 and already reported by several authors.24,25 The di€raction pattern (inset in Fig. 5) shows a straining of the reciprocal nodes along the [111]c growth axis, i.e. perpendicular to the stacking fault plane. The ®rst SiC sublayer was observed to be often dis￾continuous, particularly when its thickness was low (i.e. 0.1 mm), as shown in Fig. 2. As a result, ``mechanical bridges'' were formed under such conditions, between the sublayers (inset in Fig. 2). Obviously, an optimising of the nucleation/growth processes should be further carried out in order to achieve thinner and smoother sublayers. 3.3. Multiple interfacing The number of interfaces in the (PyC/SiC)n multi￾layered interphase increases as n is raised: up to 8 when n=4 (materials G, H, K and L) remembering that the silicon carbide in the last sequence is the matrix itself. As discussed in a previous paper,11 the ®rst interface has a unique role in controlling the behaviour of the whole interfacial sequence: ®bre/PyC1 bonding has to be strong in order to allow multiple de¯ection at the dif￾ferent other interfaces.11 Fibre surface bonding strength is related to the surface state of the ®bre. In addition to the ®rst interface (®bre/PyC1) there exists two kinds of interface characterised by a very di€erent roughness (important features regarding debonding and friction phenomena) in such multilayered (PyC/SiC)n inter￾phases. The interface related to a SiC-deposit onto a PyC￾layer (e.g. PyCnÿ1/SiCn) was usually smooth, as already mentioned, owing to the layered structure of pyr￾ocarbon and to its ``covering capability'' (tending to Fig. 4. Growth of SiC on the surface of PyC layer: smoothness of the interface. Fig. 5. Structure of the SiC-based sublayer. Inset: electron di€raction pattern centered on the contrasted crystal exhibiting one-dimensional disordered polytypism. S. Bertrand et al. / Journal of the European Ceramic Society 20 (2000) 1±13 5