Spark plasma sintering: Possibilities and limitations

Spark plasma sintering is a comparatively new technique that uses a pulsed direct current to heat the graphite pressure die and that allows very fast beating and cooling rates, short holding times and high pressures to obtain fully dense samples. We have successfully compacted a wide variety of materials, e.g. metals and alloys, functional graded materials, structural and functional ceramics and composites, and some of our recent findings will be briefly described. Recently we have studied the ductility of silicon nitride based ceramics and found that it is dramatically improved in presence an external Pulsed electric field. We have accordingly reached compressive strain rates of the order of 10(-2) s(-1) at 1500 degreesC for Si3N4-based ceramics containing less than 5 vol% inter-granular glassy phase using the SPS-unit, while performing the same experiment in a conventional hot press yielded two orders of magnitude lower strain rates. The electrical field effect will be discussed as well as limitations set for instance by the use of graphite dies.