Symmetrical three-layer mullite-matrix composites with the addition of m-ZrO2 in the outer layer and t-ZrO2 in the inner layer have been prepared by sequential freeze casting followed by sintering at 1500-1700 oC. The composites have been characterized in terms of their microstructures and mechanical properties. In this type of layered composite, the toughness and flaw tolerance can be maintained with scarcely any reduction in the fracture strength. The layered material densified at 1700 oC exhibited a maximum value of fracture strength (~215 MPa) and toughness (~6.5 MPa·m1/2). The strength of specimens with Vickers diamond indents as a result of applied loads of 9.8-294 N was measured. The contact damage resistance was superior in the layered composites when compared with monolithic ceramics, possibly due to the development of relatively large compensating residual stresses and microcracks in the outer layers and the inner layer.

Keywords: Layered composite, Freeze casting, Flaw tolerance, Toughness, Fracture strength, Contact damage resistance.