Fibrous monoliths of mullite-AlPO₄ and alumina/YAG-alumina platelets

Two-layer, fibrous monolithic composites consisting of mullite-aluminum phosphate (AlPO₄) and 50 vol.% alumina:50 vol.% YAG in situ composite matrix-alumina platelet interphase components, were fabricated by a co-extrusion technique. The four powders were characterized for particle size, specific surface area, and SEM analysis. The mixing formulations for extruding the powders were developed using ethylene vinylacetate copolymer as a binder. The variation in the mixing torque, in a Brabender mixer, as a function of temperature was measured. The binder removal behavior of the mullite-AlPO₄ fibrous monolithic composite was studied by thermogravimetric analysis (TGA). The AlPO₄ and alumina platelet interphase layers formed a porous and less porous interphase region, respectively, after sintering. The sintered mullite-AlPO₄ two-layer fibrous monolithic showed non-brittle fracture behavior. Its 3-point bend strength and work of fracture were 76 ± 5 MPa and 0.45 ± 0.02 kJ/m², respectively.