Papers by Keyword: Oxide Fibers

Abstract: In this study, it was tried to develop a process chain for ceramic injection molding of Al₂O₃-chopped-fiber reinforced oxide-ceramic-matrix-composite. The feedstocks are compounded at 50 Vol. % filling degree of solid (Al₂O₃ μ-powder (Taimei Chemicals Co. Ltd.) and 3,2 mm chopped fibers (3M)), in which fiber content varies from 0 Vol. % to 100 Vol. %. As binder system, PE + Paraffin Wax + Stearic Acid are used. The ingredients are compounded in a kneader (Brabender) at 125°C and after the viscosity measurement in the high pressure capillary rheometer at 160°C and certain shear rates, the feedstock is injection molded (Battenfeld) at 160°C, which is followed by debinding process, including chemical (in n-Hexane) and thermal steps, and 2h sintering at different temperatures. Flow paths in the machinery parts, rheological properties of binding system, fiber content and the fiber orientation have significant effect on the flow behavior of the feedstock, fiber -orientation, -distribution & -length, which are crucial to understand the properties of end-parts like mechanical reinforcement of the fibers. The fibers in the sintered parts are ca. 200 μm in average length. The fibers in the feedstock show different orientations depending on the part-geometry and the green bodies have different densities depending on sintering temperature, amount of dispersant and fiber orientation.

Abstract: Continuous fiber reinforced glass-ceramic (GC) matrix composites are potential candidates for thermomechanical applications at moderate temperatures (up to 1000°C) due to the combination of interesting properties such as high specific strength and toughness. Crack deflection into fiber-matrix interface, as well as subsequent fiber pullout and bridging are the respective toughening mechanisms. In this paper, the compatibility between LZSA glass-ceramic matrix and commercially available oxide alumina fibers (Nextel^TM 610) is qualitatively examined. Toughening mechanisms such as crack deflection and fiber pullout are investigated by analyzing the path of Vickers-induced matrix cracks formed in the vicinity of the fibers and by investigating the crack surface of bending samples, respectively. GC matrix samples sintered and crystallized at different heat-treatment conditions have shown strong interfacial bonds between matrix and fibers, which leads to a brittle fracture without significant fiber pullout in all cases. This behavior indicates the requirement of using fiber coatings in this CMC system, to produce weak interfaces that enable toughening mechanisms to take place.