400 B H 300 OTHON INPRPACP a25星星4 K C 200 0 WIX TERFACE 02 0.4 0.6 Longitudinal tensile strain(c) Fig. I. Tensile stress-strain curves obtained for 2D-SiCSiC composites with various multilayered interphases: B, D, H and L fabricated with treated Nicalon fibre; A, C, G and K fabricated with as-received Nicalon fibre(according to Refs [4] and [liD Pasquier3 has investigated the potentialities of multi- tooling. The components of the multilayered(Py C/SiC) layered(PyC/SiC)n interphases at the micrometer scale in interphases and the Sic-matrix were infiltrated within the Nicalon/SiC composites in terms of oxidation resistance porous fibre preforms, according to the isothermal/iso- Then, Heurtevent4 has developed the nanoscale multi- baric chemical vapour infiltration(I-CVI)process, which layered(PyC/SiC)n interphases in Hi-Nicalon/ SiC micro- has been described elsewhere. 6-18 Pyrocarbon and silicon composites and studied their behaviour at high carbide were deposited from propane C3Hs and methyl temperatures in oxidative conditions trichlorosilane(MTS) CH3siCl3/H2, respectively, accord The aim of the present paper is to char ng to the following overall equations: tructure of micro- and nano-scaled(Py C/SiC)n multi layered interphases. The particular aspect related to the CH3 SiC3(e) SiC+3HClgy treatment is fully described in a companion paper, s ace first interface and the influence of the fibre surf C3Hxg)→3C(+4H2g 2. Experimental procedure in a hot-wall chamber (internal diameter: 130 mm; 2.1. 2D-SiC/SiC materials obtained by 1-CVI cooled r f. coil (maximum temperature capability c1500.C). The apparatus has been designed to work The 2D-SiC/SiC composites were prepared as rectan- under reduced pressures(0.5<P<10 kPa), the total gular plates (130x 100x5 mm )from 2D-preforms con- pressure being maintained at a constant value with a sisting of stacks of Nicalon fabrics(NLM 202 ceramic pressure sensor(type 127A from MKS)and a pressure grade from Nippon Carbon Company Ltd, Tokyo, regulator(type 252A from MKS). Mass flowmeters were Japan)maintained pressed together with a graphite used to measure the flowrates of the various gaseousPasquier13 has investigated the potentialities of multi￾layered (PyC/SiC)n interphases at the micrometer scale in Nicalon/SiC composites in terms of oxidation resistance. Then, Heurtevent14 has developed the nanoscale multi￾layered (PyC/SiC)n interphases in Hi-Nicalon/SiC micro￾composites and studied their behaviour at high temperatures in oxidative conditions. The aim of the present paper is to characterise the structure of micro- and nano-scaled (PyC/SiC)n multi￾layered interphases. The particular aspect related to the ®rst interface and the in¯uence of the ®bre surface treatment is fully described in a companion paper.15 2. Experimental procedure 2.1. 2D-SiC/SiC materials obtained by I-CVI The 2D-SiC/SiC composites were prepared as rectan￾gular plates (1301005 mm3 ) from 2D-preforms con￾sisting of stacks of Nicalon fabrics (NLM 202 ceramic grade from Nippon Carbon Company Ltd., Tokyo, Japan) maintained pressed together with a graphite tooling. The components of the multilayered (PyC/SiC)n interphases and the SiC-matrix were in®ltrated within the porous ®bre preforms, according to the isothermal/iso￾baric chemical vapour in®ltration (I-CVI) process, which has been described elsewhere.16±18 Pyrocarbon and silicon carbide were deposited from propane C3H8 and methyl￾trichlorosilane (MTS) CH3SiCl3/H2, respectively, accord￾ing to the following overall equations: CH3SiC3…g† ! H2 SiC…s† ‡ 3HCl…g† …1† C3H8…g† ! 3C…s† ‡ 4H2…g† …2† in a hot-wall chamber (internal diameter: 130 mm; height: 250 mm) heated isothermally with a water￾cooled r.f. coil (maximum temperature capability: 1500C). The apparatus has been designed to work under reduced pressures (0.5<P<10 kPa), the total pressure being maintained at a constant value with a pressure sensor (type 127A from MKS) and a pressure regulator (type 252A from MKS). Mass ¯owmeters were used to measure the ¯owrates of the various gaseous Fig. 1. Tensile stress±strain curves obtained for 2D-SiC/SiC composites with various multilayered interphases: B, D, H and L fabricated with treated Nicalon ®bre; A, C, G and K fabricated with as-received Nicalon ®bre (according to Refs.[4] and [11]). 2 S. Bertrand et al. / Journal of the European Ceramic Society 20 (2000) 1±13