Non-equilibrium processing of ceramics

During recent years we have studied the consolidation of nano-powders and ceramics composites where the phase constituents of the formed compacts are not in thermodynamic equilibrium using the SPS processing technique. Our efforts have been focused on understanding the kinetics of densification/consolidation, grain coarsening, and of in situ reactions. In this communication, we will show how a non-equilibrium state can be created that in a later part of the sintering process can be used to enhance the mass-transport and the formation of tough interlocking microstructures, and how the rapid growth occurring during the consolidation of nano-sized materials can be suppressed by selectively enhancing the grain-boundary diffusion. The preparation of fully densified ceramic composites consisting of non-equilibrium phase constituents, that for instance combines a structural component, e. g. ZrO2, with a bioactive one, e. g. hydroxyapatite, will also be presented. Non-equilibrium processing opens up new possibilities for developing ceramic composites containing two or more non-equilibrium phases exhibiting unique microstructural features and properties.