Functionally graded electrical/thermal ceramic systems

Ceramic–metal and ceramic–ceramic functionally graded materials (FGMs) show promise for hypothesised applications such as thermoelectric converters, graded solid oxide fuel cells, graded piezoelectrics, electrically insulating joints, heatsinks for fusion reactors, and thermal barrier skins for lightweight spaceplanes. Most research has focussed either on FGM films (microns across), or modelling of hypothetical FGMs. Large bulk-FGMs with continuous (not layered) gradients are ideal for the above listed applications, however existing bulk-FGM powder-processing technologies give little gradient control and slow processing throughputs. The authors have developed a new process, impeller-dry-blending, which offers the possibility of producing large bulk-FGMs of a wide range of controllable continuous gradients and compositions. In this, the first published study of the impeller-dry-blending process, Cu–SiC and stainless steel–SiC FGMs were fabricated. Electron microscopy and elemental analysis revealed linear compositional gradients across cross sections of several millimetres. Densification was by vacuum sintering and hydrostatic shock forming.