Microstructure and material properties of double-network type fibrous (Al2O3–m-ZrO2)/t-ZrO2 composites

Al2O3–(m-ZrO2)/t-ZrO2 composites with a novel double-network microstructure were fabricated by multi-pass extrusion process using polymer bound ceramic green body. A simultaneous micro- and macro-level microstructure tailoring was made where unidirectionally aligned two-phase Al2O3–(m-ZrO2) fibers were enclosed in a t-ZrO2 phase connected in a network formation and this network was further enclosed in a thicker t-ZrO2 phase. Composite green rods were hot extruded and reassembled in parallel for extrusion and after several passes of extrusion very fine microstructure with dimension of a few micrometers was obtained. Material properties such as hardness, bending strength and fracture toughness were measured for the composites. Microstructure characterization was carried out by SEM technique. In the 4th passed Al2O3–(m-ZrO2)/t-ZrO2 composites, the outer network of t-ZrO2 was 15 μm, inner network 0.8 μm and the inner Al2O3–(m-ZrO2) core was 2.5 μm. The highest hardness, fracture strength and toughness values were about 1452 Hv, 1006 MPa and 8.6 MPa m1/2, respectively, in the sample sintered at 1500 °C.