A process is developed whereby thin ceramic substrates layered with a coating are induced to adopt a different shape at elevated temperature without the application of external pressure. To achieve such deformation, thin beams of alumina are coated with magnesia, calcia, or silica; these composite beams are then heated to high temperature where deformation occurs. Scanning electron microscopy and compositional profiling indicate that for MgO and CaO coatings on alumina, a bilayer structure forms. For SiO2 coatings on alumina, silicon is found throughout the substrate. A viscoelastic mechanics model based on strain mismatch in bilayer systems indicates how the curvature depends on the thickness of the two regions. A mechanistic model is presented that describes the strain mismatch in terms of the degree of conversion to a new phase, the amount of differential sintering between layers, and the amount of residual porosity present in the two layers of the substrate.

Keywords: alumina; magnesia; layered composites; strain mismatch