THE EFFECT OF THE FIBER/MATRIX INTERFACE ON THE MECHANICAL PROPERTIES OF CERAMIC-REINFORCED ZIRCONIA PHOSPHATE-BASED MATRIX COMPOSITES

Hot-pressed and phosphate-bonded zirconia phosphate-based matrix composites were fabricated for use as a composite faceplate in a sandwich structure radome wall. These composites were reinforced with either mullite whisker-mats or different grades of Nicalon (TM) SiC fibers (Nippon Carbon, Tokyo, Japan). The fibers were either in tow or cloth form and were uncoated or coated with thin debond layers of BN or C. The strength, fracture toughness, and retained up shock strength of the various composites were measured. These results were correlated with the resultant microstructure of the reinforcement/matrix interface. SEM and TEM revealed the presence of a wide variety of interphases including the formation of SiP(2)O(7) reaction layers. The presence of intact debond coatings and semi-porous reaction layers led to composites with better strength and toughness. Degradation of some of these interphases during thermal up shocking of 1200 degrees C led to embrittlement of the composite faceplates.