COMPOSITES SCIENCE AND TECHNOLOGY ELSEVIER Composites Science and Technology 61(2001)607-614 Oxidation behaviour of a multi-layered ceramic-matrix composite(SiC)r/C/(sibC)m J. P. Viricelle, P. Goursat*, D. Bahloul-Hourlier S.P.C.T.S., U.R.A. CNRS 6638, Universite de Limoges, 123, Av. Albert Thomas, 87060 Limoges Cedex, france Received 2 July 1999; accepted 6 December 2000 Abstract The oxidation behaviour of a 2.5D multi-layered ceramic-matrix composite (Sic)/C/(SiBC)m was investigated in a dry atmo- sphere O2(20 vol %)CO2(5 voL % He and in the presence of water vapour H20 (2.3 vol %) The matrix denoted (SiBC)m constituted of three phases: silicon carbide, boron carbide and a SibC phase. The aim of boron incorporation is to improve the oxidation resistance of the composite by boron oxide or borosilicate formation. The transformations were followed by thermo- gravimetry during isothermal experiments of 20 h exposure in the range 600-1200 C and the changes of the specific area of the ples were measured by krypton adsorption at 77K. The results of this study show that effective protection occurs in the range 650-900oC and is mainly related to the oxidation of boron carbide. At higher temperatures, boron oxide is no longer protectiv because of its volatilisation and consumption by reaction with water vapour. However, the two other constituents of the matrix, C and SiBC, lead to self-healing behaviour by both borosilicate and silica formation. C 2001 Published by Elsevier Science Ltd Keywords: Ceramic-matrix composite; Oxidation 1. ntroduction boron-containing composites [12, 13 revealed that the formation of a borosilicate layer was efficient in limiting Ceramic-matrix composites(CMCs) reinforced with oxidation. Some new composites have therefore beer continuous Sic-based fibers exhibit attractive properties developed on the basis of a(SiC)/C/(SiC)m structure or thermostructural applications, including low den- but with the incorporation of boron compounds in the sity, high strength and non-brittle mechanical beha- matrix [14]. In this paper, a study of the oxidation viour. This last property is controlled by the presence of behaviour of a 2. 5D multilayered matrix composite with an interphase between the fibers and the matrix. The silicon carbide fibers and a carbon interphase is pre- interphase, which often consists of pyrocarbon, allows fiber debonding and crack deflection with energy dis- sipation [1-3]. Nevertheless, a critical aspect of the tance of the interphase [4-7. The erosion of the carbo- naceous structure by oxidation alters the properties of The experimental techniques used for the composite the medium and thus affects the durability of the cera- haracterisation were optical microscopy (Olympus mic material [8]. An answer consists in replacing the Mo61)and scanning electron microscopy (Philips pyrocarbon interphase by a boron nitride Bn inter- XL30) for morphology and architecture observations, phase [9-11]. However, modelling of the oxidation of a and microanalysis and X-ray diffraction (Philips (SiC)f/C/( SiC)m composite [4, 5] has shown that self- DW1130)for the determination of the composition and healing behaviour consisting in crack closure by silica nature of the phases. Specific area measurements formation occurred above 1000C, and other studies on (Micromeritics ASAP2000) were performed with iso- thermal krypton adsorption experiments at 77 K in s Corresponding author. Fax: +33-05-55-45-75-86 order to follow the variation of the reactive area after E-mail address: goursat(@ unilim fr(P Goursat) oxidation treatments of the samples 0266-3538/01/S.see front matter C 2001 Published by Elsevier Science Ltd. All rights reserved PII:S0266-3538(00)00243-8
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