The project concerned evaluation of electrophoretic deposition as a forming technique for making ceramic laminates with complex shape. In addition new concepts for creating interfacial microstructures have been studied, which allow flexibility in regard to the materials that can be made. This was based on the idea of using a porous structure to give an interlayer of suitable properties and constitutes a general way of making tough laminates irrespective of the ceramic powders used.
For evaluation of electrophoretic deposition as a forming technique for ceramic laminates, the electrophoretic deposition of silicon carbide laminates with graphite interlayers was developed. This comprised the formulation of a suspension from which silicon carbide deposits could be obtained which sinter to a high density, and selection of a graphite suspension for deposition of the graphite interlayers. For sintering of silicon carbide, carbon and boron are used as sintering additives. Sintering studies within the project have shown that carbon addition ensures that the silica is removed from the surface of the silicon carbide powder before it can be reduced directly by the silicon carbide. If the latter reaction occurs, this results in the formation of large pores, which do not heal during sintering.
Furthermore, general guidelines for suspension preparation for (EPD) have been proposed and the mechanism of deposition has been investigated. Also, the microstructures of the graphite interlayers has been investigated using transmission electron microscopy. It is important to add polymeric binders to the graphite suspensions which yield a sufficient carbon residue after pyrolisis to bind the graphite flakes together. The use of porous interlayers as an alternative for graphite interlayers, has been shown to result in reliable crack deflection using alumina/porous alumina laminates. The pores have been found to be thermally stable and sintering studies have shown that up to 55 vol% of fugitive inclusions in a layer does not alter the sintering behaviour of such a layer compared to the sintering of a layer containing no fugitive inclusions.