Ultra-high temperature ceramics by spark plasma sintering

The prominent contribution played by the SPS technology for the fabrication of bulk components consisting of Ultra High Temperature Ceramics (UHTCs) is analyzed in this work. To this aim, several studies addressed to the obtainment of highly dense monophasic transition metal borides/carbides, binary/ternary composites, whiskers/fibers reinforced materials, high-entropy ceramics, as well as porous graded structures are described and discussed. In particular, the use of the reactive sintering approach is compared with a two-steps (non-reactive) route, based on the preparation of UHTC powders by self-propagating high-temperature synthesis (SHS) prior to their consolidation. The latter procedure is generally found more convenient and versatile for the fabrication of this class of ceramics, whose reactions of formation are highly exothermic, so that their synthesis processes are prone to evolve under the difficult-to- control combustion regime. The high relative densities reached by the SPS products, as well as the corresponding mechanical, oxidation resistance and optical properties, are very promising for their wide diffusion in several industrial areas where severe environmental conditions have to be withstood, such as in the aerospace and solar energy fields.