Scripta Materialia, Vol. 38. No -5.1998 Lhe PIIS13596462(97)00443-0 MICROSTRUCTURAL DESIGN IN ALUMINA-ALUMINA/ZIRCONIA LAYERED COMPOSITES A Javier Sanchez-Herencia, Jose S Moya*and Antoni P. Tomsia *Instituto de Ceramica y Vidrio(CSIC), Arganda del Rey, 28500 Madrid, Spain Materials Sciences Division, Lawrence Berkeley Laboratory 1 Cyclotron Road, Berkeley, ( Received April 28, 1995) (Accepted October 7, 1997) Introduction Very recently several authors(1-4) have pointed out the extremely important role of microstructural design in developing structural ceramic materials for long term high temperature applications. In this sense Raj [4] has identified several boundary conditions: (i) Resistance to oxidation, (ii)Resistance to grain boundary sliding and cavitation. (ifi) Good strength and toughness at room temperature The aspiration is to eliminate grain boundaries which can act as cavitation sites, without using single crystals which typically exhibit low toughness. In this regard ceramics with single crystal-like mor- phologies, e.g., large elongated grains, with good fracture toughness and high bending strength ha One route to find these apparently contradictory characteristic is by building up layered microa chitectures where layers with high toughness and high bending strength coexist with layers with high creep resistance. These conditions can be met in the case of Al2O3/Al2O3-Zro2 laminates The present work was directed to the study of the microstructural features and properties of AL2O3/Al,O3+ unstabilized ZrO2 and Al2O/Al2O3+ t-ZrO2(3 mol%Y2O3layered composites Experimental Procedure The following starting materials have been used: Al2O3( Condea HPA 0.5, Germany) with dso -0.5 um, specific surface area of 9.5 m/g and 99.99% purity; monoclinic ZrO2 (Dinamit Nobel, Germany) with dso -1 um and specific surface area of 66.7 m-g and tetragonal ZrO2(3 mol%Y2O3)(TZ-3Ys Tosoh, Japan)with dso 0.4 um and specific surface area of 6.7 m-7 Stable aqueous suspensions of Al2O3, A,O3+15 vol m-zrO2 and Al2O3+15 vol %t-ZrO2(Y2O3) ith 70 wt solid load were prepared by adjusting the pH with HCl to a value (5)of 4. The rheological properties of the different slips were studied using a rotational viscosimeter(Haake Rotovisco HV20) at a constant temperature of 25C. Monolithic and laminated composites were obtained following the flow chart of Fig. 1. The thickness of the different layers in the laminate compacts were calculated using the Al2O3 wall thickness ratio(Fig 2) Flexural strength test sample bars with dimensions of 40 x 4 X 2 mm were cut from fired plates with tensile surfaces oriented parallel to the layers. Surfaces were polished successively with 9, 6 and I um