Materials` Days at the University of Rostock / International Workshop 2011

Prof. Simo-Pekka Hannula,

Department of Materials Science and Engineering, Aalto University School of Chemical Technology, Finland
materials.aalto.fi/en/index/

Curriculum Vitae

You find it here as a pdf-file.

His Topic of Materials' Days 2011:

Processing of Hybrid Materials by Pulsed Electric Current Sintering (PECS)

Abstract:
Application of AC or DC fields during sintering has been shown to be effective in lowering processing temperatures necessary for the elimination of porosity and reducing grain growth. The effect is essentially athermal, i.e., independent of heating rate and sintering temperature. The use of electric current also enables higher heating rates and shorter holding times. Therefore it is possible to sinter powders near theoretical density with little grain growth very effectively. Additionally the use of electric current enables sintering of materials, which by conventional methods would be difficult or impossible to sinter.
Patents regarding the use of electric current to enhance sintering have been issued since the beginning of 1920s. Nowadays electric current assistant sintering is commonly used in combination of hot pressing. The low-voltage, high amperage current goes through both die and the compact providing both uniform and fast heating. Typically, pulsed current is utilized. Pulsed current provides high heating rates and activates sintering in the microstructural level e.g. by accelerating neck growth due to discharge spark. The importance of FAST sintering methods in industrial scale is still rather limited, but increasing at an accelerating rate since the late 1990s. The FCT HP D 25-2 PECS unit was taken in use at Aalto University in 2008 in order to make the technology known to the Finnish industries.
PECS has been used successfully since for compacting of various materials including several composite materials such as WC-8Co, WC-12Co Cu-Cu₂O, Cu-Al₂O₃, Cu-ND, Cu-TiB₂, Ultimet-TiC, Ni-Mn-Ga- WC and Al₂O₃/ZrO₂ nanocomposites with different solid lubricants. A new area of application is compaction of hybrid materials. This includes compaction of CN and Ce_0,9Gd_0,1O_1,95 based materials for targets to be used in producing PVD coatings of corresponding structures. PECS has also been studied recently for compacting of magneto-optical materials from hybrid sol-gel derived SiO₂ –Fe₃O₄ powders. The results obtained so far will be presented, and challenges in compaction of such materials will be discussed.