INTERFACIAL MICROSTRUCTURE AND CHEMISTRY OF SIC BN DUAL-COATED NICALON-FIBER-REINFORCED GLASS-CERAMIC MATRIX COMPOSITES/

Glass-ceramic composites with improved high-temperature mechanical pro perties have been produced by incorporating continuous SiC fibers into a barium magnesium aluminosilicate matrix. Control of the fiber/matri x interface was achieved by a dual-layer coating of SiC/BN(C) applied to the fibers by CVD. The weakly bonded interface resulted in composit es with high fracture toughness and strength up to 1100-degrees-C, and the composite system was oxidatively stable during long-term exposure to air at high temperatures. Composites with different thermal and me chanical histories were studied, and interfaces were characterized usi ng transmission electron microscopy (TEM), Auger electron spectroscopy , and fiber pushout tests. Observations of interfacial microstructure were correlated with the mechanical properties of the composite and wi th interface properties determined from fiber push-out tests.