Application of deformation instability to microstructural control in multilayer ceramic composites

Bimaterial interfaces are known to be unstable against perturbation, due to flow localization, during deformation. In this paper a criterion for flow localization is formulated. based on the difference in flow properties of t he constituent phases. It predicts a tensile force in the harder phase and an equivalent compressive one in the softer phase, leading to necking of th e harder phase. A useful practical application of this instability is demon strated in the production of a series of oxide/oxide composites with micros tructures ranging from laminar to wood-like in texture. Composites of Ce-Zr O2/Al2O3 with strong interfaces demonstrate high strength (1.1 GPa), fractu re toughness (17 MPa rootm) and hardness (12 GPa) due to greatly increased phase transformation. Alternatively, composites of Y-ZrO2/porous-Al2O3 and Y-ZrO2/YPO4 display crack deflection and graceful failure due to the presen ce of weak interfaces. The potential now exists for this deformation proces sing technique to be applied to the production of 3-D composites with isotr opic properties. (C) 2001 Elsevier Science BN. All rights reserved.