PREPARATION AND CHARACTERIZATION OF 2D SIC SIC COMPOSITES WITH COMPOSITION-GRADED C(B) INTERPHASE/

20 SiC/C(B)/SiC composites were prepared by CVI. The C(B) interphase i s made of five successive C(B) layers with increasing boron content fr om the fibre to the matrix. This composition-graded interphase leads t o good mechanical properties similar to those obtained with pure pyroc arbon interphase. However, the lifetime in air under load at high temp erature of 2D SiC/C(B)/SiC composites is not improved despite the high percentage of baron in several sublayers of the interphase. By TEM ch aracterization, the boron-rich layers were found to exhibit a nano-por ous texture probably due to a bad control of rite growth process withi n the fibrous preforms. This nanoporous texture might be responsible f or the poor oxidation resistance of these sublayers and consequently t he rather short lifetime of the real 2D composites with respect to tho se previously reported for 1D SiC/C(B)/SiC model microcomposites. (C) 1997 Elsevier Science Limited.