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 the constituent phases. It predicts a tensile force in the harder phase and an equivalent compressive one in the softer phase, leading to necking of the harder phase. A useful practical application of this instability is demonstrated in the production of a series of oxide/oxide composites with microstructures ranging from laminar to wood-like in texture. Composites of Ce–ZrO2/Al2O3 with strong interfaces demonstrate high strength (1.1 GPa), fracture toughness (17 MPa√m) and hardness (12 GPa) due to greatly increased phase transformation. Alternatively, composites of Y–ZrO2/porous–A12O3 and Y–ZrO2/YPO4 display crack deflection and graceful failure due to the presence of weak interfaces. The potential now exists for this deformation processing technique to be applied to the production of 3-D composites with isotropic properties.