S Jacques et al./Journal of the European Ceramic Society 20(2000)1929-1938 and equivalent in thickness. The total interphase thick form. In any cases, this interface observation (per- ness is about 450 nm. While the interface between both formed after mechanical test) does not reveal any sublayers is regular and linear, the interphase /matrix debonding interface appears on this scale irregular ("serrated") Close to the fibre surface, the deposited BN appears first owing to the growth of extended coherent domains(cor- poorly organised with limited coherent domains and 002 responding to high bright/dark contrast areas)where bn planes orientated at random. Then, the degree of struc organisation is very high. On the contrary, the weak tural anisotropy increases progressively from the fibre to contrast of the second sublayer located near the fibre the interface of both interphase sublayers (i.e. Fig 9, from evidences a poorer crystallographical orga nisation the left to the right): the coherent domains expand along The SAD patterns performed in both sublayers(Fig. stacking c axis(ranging from 10 to 15 fringes)as well as are typical, with their 002 arcs, of an anisotropic tur- longitudinally (parallel to the fibre axis)(fringes length matrix, spots occurrence in the SAD pattern reveals the denced within the first BN interphase sublayer ent is evi- bostratic material. For the sublayer located near the 10 nm)(Fig. 10, left). Thus, a structural gradi local existence of bn submicrometric polycrystalline structures. Furthermore, the smaller arc length(or arc- opening angle in azimuth) evidences a better 002 planes 200nm average orientation than near the fibre HR observation of fibre/Bn interface(Fig. 9, left) shows that it is made of a thin amorphous sublayer (thickness <5 nm). This layer can(i) either result from a Hi-Nicalon fibre surface carbon enrichment, 12-14 or(ii)be Bn that begins to depositate on the fibre in amorphous matrixes SAD SAD 、 Fig. 6. SeM observations of the failure surface batch 3 mini Fig. 8. Bright-field TEM image of the interfacial zone of a batch 2 composite:(a) smooth pulled out fibres;(b)BN interphase fixed minicomposite and corresponding SAd patterns(negatives) pulled out fibre 400nm Fig. 7. Bright field TEM image of the interphase of a batch 2 mini- Fig 9. HR-TEM image of the interphase of a batch 2 minicompositeand equivalent in thickness. The total interphase thick￾ness is about 450 nm. While the interface between both sublayers is regular and linear, the interphase/matrix interface appears on this scale irregular (``serrated'') owing to the growth of extended coherent domains (cor￾responding to high bright/dark contrast areas) where BN organisation is very high. On the contrary, the weak contrast of the second sublayer located near the ®bre evidences a poorer crystallographical organisation. The SAD patterns performed in both sublayers (Fig. 8) are typical, with their 002 arcs, of an anisotropic tur￾bostratic material. For the sublayer located near the matrix, spots occurrence in the SAD pattern reveals the local existence of BN submicrometric polycrystalline structures. Furthermore, the smaller arc length (or arc￾opening angle in azimuth) evidences a better 002 planes average orientation than near the ®bre. HR observation of ®bre/BN interface (Fig. 9, left) shows that it is made of a thin amorphous sublayer (thickness<5 nm). This layer can (i) either result from a Hi-Nicalon ®bre surface carbon enrichment,12ÿ14 or (ii) be BN that begins to depositate on the ®bre in amorphous form. In any cases, this interface observation (per￾formed after mechanical test) does not reveal any debonding. Close to the ®bre surface, the deposited BN appears ®rst poorly organised with limited coherent domains and 002 planes orientated at random. Then, the degree of struc￾tural anisotropy increases progressively from the ®bre to the interface of both interphase sublayers (i.e. Fig. 9, from the left to the right): the coherent domains expand along stacking c axis (ranging from 10 to 15 fringes) as well as longitudinally (parallel to the ®bre axis) (fringes length 10 nm) (Fig. 10, left). Thus, a structural gradient is evi￾denced within the ®rst BN interphase sublayer. Fig. 6. SEM observations of the failure surface batch 3 mini￾composite: (a) smooth pulled out ®bres; (b) BN interphase ®xed on pulled out ®bre. Fig. 7. Bright ®eld TEM image of the interphase of a batch 2 mini￾composite. Fig. 8. Bright-®eld TEM image of the interfacial zone of a batch 2 minicomposite and corresponding SAD patterns (negatives). Fig. 9. HR-TEM image of the interphase of a batch 2 minicomposite near the ®bre. S. Jacques et al. / Journal of the European Ceramic Society 20 (2000) 1929±1938 1933