Oxidation behaviour of a multi-layered ceramic-matrix composite (SiC)f/C/(SiBC)m

The oxidation behaviour of a 2.5D multi-layered ceramic-matrix composite (SiC)(f)/C/(SiBC)(m) was investigated in a dry atmosphere O-2 (20 Vo1.%) CO2 (5 vol.%) He and in the presence of water vapour H2O (2.3 vol.%). The matrix denoted (SIBC)(m) is 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 thermogravimetry during isothermal experiments of 20 h exposure in the range 600-1200 degreesC and the changes of the specific area of the samples were measured by krypton adsorption at 77 K. The results of this study show that effective protection occurs in the range 650-900 degreesC and is mainly related to the oxidation of boron carbide. At higher temperatures, boron oxide is no longer protective because of its volatilisation and consumption by reaction with water vapour. However, the two other constituents of the matrix, SiC and SiBC, lead to self-healing behaviour by both borosilicate and silica formation. (C) 2001 Published by Elsevier Science Ltd. Ail rights reserved.