Fabrication of Continuous‐Fiber‐Reinforced Polycrystalline Oxide Composites via Molten Salt Infiltration

A novel molten nitrate salt infiltration technique was developed for the fabrication of continuous‐fiber‐reinforced polycrystalline‐alumina‐matrix composites containing a high volume fraction (47%) of small‐diameter fibers (Du Pont PRD 166 alumina/zirconia; 20‐μm diameter). A single infiltration resulted in sufficient matrix yield to permit densification of the resulting composites to >93% of theoretical density with excellent microstructural uniformity. Hot‐pressed composites fabricated in this manner exhibited Young's modulus of 270GPa, flexural strengths of 272 ± 20 MPa, and fracture toughness of 3.35 ± 0.37 MPa·m^l/2. Primary fracture origins were localized regions of interfiber porosity, which were attributed to incomplete fiber tow infiltration. Fractographic analysis revealed lack of fiber pullout, and emphasized the need for interfacial debonding agents (coatings) to achieve further toughening. Results have demonstrated the utility of molten‐salt‐matrix precursors for the fabrication of polycrystalline‐matrix composites containing high volume fractions of continuous, small‐diameter ceramic fibers.