Forming of Ceramics during Firing without the Application of External Pressure

Abstract

A method to form thin ceramic bodies is described in which curvature in the component is introduced at high temperature without the application of an external stress. The internal stress that drives the deformation results as a consequence of cation penetration from a coating into a substrate material. This technique has been developed for alumina substrates that are coated with layers of chromia, magnesia, titania, calcia, silica, and iron oxide. Normalized deflections of segment height to sample thickness (A/t) of up to 10 were observed for samples with beam geometry and A/t values of 4 were obtained for disks. The magnitude of the deflection is dependent on the amount of dopant that is applied, as well as the soak temperature and time. An analytical model has been developed to describe the magnitude of the deflections. The best agreement with the experimental data is obtained when the deflections are treated as occurring at high temperature, where the resistance to bending from stiffness effects is reduced. This forming method is shown to be suitable to produce shapes of moderate complexity, such as ceramic wave springs.