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 is made of five successive C(B) layers with increasing boron content from the fibre to the matrix. This composition-graded interphase leads to good mechanical properties similar to those obtained with pure pyrocarbon interphase. However, the lifetime in air under load at high temperature of 2D SiC/C(B)/SiC composites is not improved despite the high percentage of baron in several sublayers of the interphase. By TEM characterization, the boron-rich layers were found to exhibit a nano-porous texture probably due to a bad control of rite growth process within the fibrous preforms. This nanoporous texture might be responsible for the poor oxidation resistance of these sublayers and consequently the rather short lifetime of the real 2D composites with respect to those previously reported for 1D SiC/C(B)/SiC model microcomposites. (C) 1997 Elsevier Science Limited.