Shaping Equipment

Spark Plasma Sintering System

© Fraunhofer IFAM Dresden
Scheme of a SPS-system 1 pulsed current generator 2 pressing tool with sample 3 upper punch 4 lower punch 5 water-cooled vacuum chamber
© Fraunhofer IFAM Dresden
SPS system at Fraunhofer IFAM Dresden

The process

The Spark-Plasma-Sintering-Process can be understood as a modified hot pressing technique. The sample is heated by a pulsed electric current which flows through the punch-die-sample-assembly using a high current and low voltage. In contrast to other sintering techniques a special preparation of the sample, i.e. by cold pressing, is not necessary, because the powder is filled directly in the mould.

It is expected that during sintering the following mechanisms take place: At the comparatively small contacts between the powder particles or rather in small gaps between them an electrical discharge may occur due to the short current pulse (pulse length: approx.3ms). Close to this microscopic electric arc local and temporally limited high temperature and pressure emerge. Thereby gases and moisture that have been adsorbed on surfaces are eliminated and oxide layers can be broken. This has an activation effect on the sintering process [1,2].

During the later phase of sintering Joule’s heat is generated due to the current flow especially at places of high electrical resistance and temporary overheats the sample while the overall sintering temperature is relatively low.

The direct heating of the die-punch-sample assembly allows very high heating rates (>300°C/min) and short sintering times in the range of a few minutes.

 

Materials

Due to the activation of the surface and the direct heating of the sample it is possible to sinter materials and combinations of materials when their compaction is either not possible or not economical.

Furthermore it is possible to compact materials with fine and homogenous microstructure with only little modification of the grainsize during sintering. The possibility to sinter materials almost without grain growth makes the SPS-Process a relevant technique for the compaction of nanostructured powders. Besides SPS allows the adjustment of temperature gradients during densification and therefore enables the fabrication of functionally graded or layered material structures with strongly differing properties (i.e. ZrO2/stainless steel, Al2O3/Titan).

Within different projects Fraunhofer IFAM Dresden deals primarily with the short time sintering of nanostructured and ultrafine granular materials.

 

Equipment

Currently approximately 250 SPS- Systems have been installed worldwide, whereof about 10 are located in Europe. Beside another plant in the USA, (Davis, CA), the other machines are installed in East Asia(predominantly in Japan, South Koreaand China). The majority of the SPS-Machines are used for research and development. With the installation of FCT-HP D 250/1 of the company FCT Systeme GmbH, Rauenstein, it is possible to fabricate sintered compacts in a product relevant size (max. diameter: 300mm) for the first time in Europe.

 

Literature:

[1] M.Tokita: Mechanism of Spark Plasma Sintering and its application to ceramics, Nyn Seramikkasu 10, 1997, S.43-53
[2] M. Ishiyama: Plasma Activated Sintering (PAS) System, Proceeding of the 1993 Powder Metallurgy World Congress, Kyoto 1993, S.931