1930 S Jacques et al. Journal of the European Ceramic Society 20(2000)1929-1938 Three batches of minicomposites called 1, 2 and 3 containing BN interphases obtained respectively with a tow rate r of 2, 2.5 and 3 m/h were prepared. A fourth batch called 0 with a pyrocarbon(PyC) interphase was also prepared in order to be used as reference. The pyrocarbon was infiltrated by CVI but using a classical induction device (i.e. constant pitch of coil turns and consequently one hot area) from propane (@cHs=9.6 cm'min-)under a pressure of 10 kPa and with r=6 m/h. Argon was used as the gas vector (@Ar=38.5 cm3 min-). The maximum temperature in the centre of the hot area was 1050oc. unlike the bn interphase infiltration, gas inlet and outlet were permuted in order to have a gas flux and a tow displacement in reverse Fig 1. Schema matics of a minicomposite prepared by CVi(for clarity, only direction and thus a good adhesion between the fibre a few fibres out of the 500 that constitute a whole tow are represented) and the coating through the susceptor. The outlet reactor winding around 2.3. SiC matrix processing a second spool controlled the fibre travelling rate r Thus, the reactor contained three distinct hot areas with flow rate was 70 cm p e For BN interphase processing, a specific temperature The Sic matrix was infiltrated by classic profile was obtained inside the susceptor thanks to second reactor from CH3 SiCl3/H2 precursor gases at variable pitch of induction heating coil turns(Fig. 2). 1100C. The ratio @1 CH,SiCh, was 0.75, the d 5 The respectively a"low temperature(<1100C), a medium duration of matrix infiltration was 5 h. maximum temperature (1150C) and a high one (1250C). The control of the fibre displacement (r) 2. 4. Charaterization through the hot areas allowed to determine the duration of the CvI treatment and consequently the interphase 2. 1. Mechanical behaviour thickness. BF3/NH3 were the gas precursors of BN. The minicomposites were tensile tested at room tem- argon was used as the gas vector but also to dilute the perature with unloading-reloading cycles using a MTS reactive species. The total gas flow rate Q was 60 cm Adamel DY-22 machine(Ivry sur Seine, France)equip- then gripped into the testing machine h an extensometer (Ingstrom, Cat. No. 2620-602 travel: 2.5 mm, type dynamic, code value 136)directly gripped on the minicomposite itself. The extensometer 7 A 90. 70060 gauge length(Lg) was 40 mm. Five tests per batch were carried out fibre tow In order to evaluate the fibre/ nding. the interfacial shear stress t was estimated by following the same methods as those used by bertrand et al. They are presented in outline below The first method considers, for unloading-reloading cycles, the width SA of the hysteresis loop at a given en by Eq(1) b2N(1-a1)R/ Er Fig. 2. Schematics of the TG-CVI reactor(a) and susceptor tempera dthrough the susceptor. The outlet reactor winding around a second spool controlled the ®bre travelling rate r. For BN interphase processing, a speci®c temperature pro®le was obtained inside the susceptor thanks to a variable pitch of induction heating coil turns (Fig. 2). Thus, the reactor contained three distinct hot areas with respectively a ``low'' temperature (<1100C), a medium maximum temperature (1150C) and a high one (1250C). The control of the ®bre displacement (r) through the hot areas allowed to determine the duration of the CVI treatment and consequently the interphase thickness. BF3/NH3 were the gas precursors of BN, argon was used as the gas vector but also to dilute the reactive species. The total gas ¯ow rate Q was 60 cm3 minÿ1 . The gas composition was: QNH3 /QBF3 =0.5 and QAr/(QBF3 +QNH3 )=0.222. The gas pressure was 20 kPa. Three batches of minicomposites called 1, 2 and 3 containing BN interphases obtained respectively with a tow rate r of 2, 2.5 and 3 m/h were prepared. A fourth batch called 0 with a pyrocarbon (PyC) interphase was also prepared in order to be used as a reference. The pyrocarbon was in®ltrated by CVI but using a classical induction device (i.e. constant pitch of coil turns and consequently one hot area) from propane (QC3H8=9.6 cm3 minÿ1 ) under a pressure of 10 kPa and with r=6 m/h. Argon was used as the gas vector (QAr=38.5 cm3 minÿ1 ). The maximum temperature in the centre of the hot area was 1050C. Unlike the BN in®ltration, gas inlet and outlet were permuted in order to have a gas ¯ux and a tow displacement in reverse direction and thus a good adhesion between the ®bre and the coating.6 2.3. SiC matrix processing The SiC matrix was in®ltrated by classical CVI in a second reactor from CH3SiCl3/H2 precursor gases at 1100C. The ratio QH2 /QCH3SiCl3 was 0.75, the total gas ¯ow rate was 70 cm3 minÿ1 and pressure 5 kPa. The duration of matrix in®ltration was 5 h. 2.4. Charaterization 2.4.1. Mechanical behaviour The minicomposites were tensile tested at room tem￾perature with unloading-reloading cycles using a MTS￾Adamel DY-22 machine (Ivry sur Seine, France) equip￾ped with a 1 kN load cell. The minicomposite ends were glued within 50 mm distant metallic tubes that were then gripped into the testing machine jaws. The cross￾head speed was 0.1 mm/min. The strain was measured with an extensometer (IngstroÈm, Cat. No. 2620-602, travel: 2.5 mm, type dynamic, code value 136) directly gripped on the minicomposite itself. The extensometer gauge length (Lg) was 40 mm. Five tests per batch were carried out. In order to evaluate the ®bre/matrix bonding, the interfacial shear stress  was estimated by following the same methods as those used by Bertrand et al.7 They are presented in outline below. The ®rst method considers, for unloading-reloading cycles, the width 
of the hysteresis loop at a given stress '.  is given by Eq. (1):8  ˆ b2N 1 ÿ a1Vf ÿ
2 Rf 2V2 fEm 2 p 
0 p 1 ÿ 0 p   …1† with a1 ˆ Ef E0 and Fig. 1. Schematics of a minicomposite prepared by CVI (for clarity, only a few ®bres out of the 500 that constitute a whole tow are represented). Fig. 2. Schematics of the TG-CVI reactor (a) and susceptor tempera￾ture pro®le (b). 1930 S. Jacques et al. / Journal of the European Ceramic Society 20 (2000) 1929±1938