Interface Engineering in Alumina/Glass Composites

The work done in the past three years has demonstrated the feasibility of developing alumina fiber based glass matrix composites for structural applications by applying an interface engineering approach. Composites consisting of a glass matrix containing coated and uncoated continuous alumina type fibers, were produced by slurry impregnation method. A tin dioxide coating was used for the PRD-166 alumina zirconia fiber, while a boron nitride coating was used for the Nextel 480 alumina silica boria fiber. Coatings were applied by chemical vapor deposition CVD. Important parameters in the coating process, in order to obtain a uniform coating on the fiber surface, are the deposition temperature and time. Tin dioxide coating forms an effective barrier between alumina and glass, and thereby prevents strong chemical bonding between the components of this composite system. Improvements in mechanical properties can be achieved by incorporation of such fibers into a brittle matrix. The primary mode of toughening in coated PRD-166 glass composites is crack deflection and fiber bridging while in coated Nextel glass and Saphikonglass composites, fiber pullout also occurs. A strong potential exists for enhancing toughness even further provided the surface roughness of the interfaces can be controlled. Preliminary tests carried out on smooth single crystal alumina fiber reinforced glass matrix composites have indicated that extensive fiber matrix debonding and pullout can result with SnO2 coating.