Interface Characterisation by Transmission Electron Microscopy and Auger Electron Spectroscopy in Tough SiC Fiber (Nicalon)-SiC Matrix Composite with a Boron Nitride Interphase

The toughness of SiC fiber (Nicalon)/SiC matrix composites is increased when an interphase, made of a soft material (e.g. pyrocarbon or boron nitride) and playing the role of a mechanical fuse, is present at the fiber-matrix interfaces. The BN-interphase, deposited from a gaseous BF3-NH3 precursor, has been analyzed both chemically and microstructurally by TEM and AES, as well as the associated fiber-interphase and matrix-interphase interfaces. The sequence of materials observed at the fiber-matrix boundary is: SiC matrix/BN interphase/SiO2/carbon/Nicalon fiber.