SiC/SiC Composites Prepared with a BN Interphase Processed by LP-CVD from Molecular Precursor

Abstract

A BN interphase has been deposited by infiltration of a Hi-Nicalon fibre tow in a Low Pressure Chemical Vapour Deposition reactor using a boron nitride molecular precursor: the tris(dimethylamino)borane (TDMAB), an halogen-free precursor. This precursor prevents fibre and CVD apparatus from chemical damage. Then SiC/BN/SiC 1D mini-composites were produced by classical CVD of SiC from hydrogen and methyltrichlorosilane mixture. The interphase composition was characterised using FT-IR and XPS analyses and the presence of carbon in the BN has be related to surface pollution and not from carbon bounded to the coating. The tensile properties of the mini-composites were tested with unload-reload cycles and have shown very good mechanical properties corresponding to a high interfacial shear stress. The observations of the interphase using TEM reveal that it is made of an anisotropic turbostratic BN. The fibre/matrix debounding, which occurs during mechanical loading, was shown to be located within the BN interphase.