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Influence of reactive atmosphere components on outgassing and sintering of hard metal mixtures

Einfluss der Komponenten einer reaktiven Atmosphäre auf das Ausgasen und Sintern von Hartmetallgemischen
: Gestrich, T.; Leitner, G.; Jaenicke-Rößler, K.

Danninger, H. ; European Powder Metallurgy Association -EPMA-:
Euro PM 2004, Powder Metallurgy World Congress & Exhibition. Conference proceedings : Vienna, Austria, 17 - 21 October 2004
Shrewsbury: EPMA, 2004
ISBN: 1-89907-215-2
Powder Metallurgy World Congress & Exhibition <2004, Vienna>
Conference Paper
Fraunhofer IKTS ()
reactive atmosphere component; outgassing process; sintering process; hard metal mixture; thermoanalytical method; heat treatment; debinding process; decomposition process; impurity reduction; metal binder phase melting; thermogravimetry; mass spectrometry; thermodilatometry; differential scanning calorimetry; DSC; production process

Outgassing and sintering ofhard metal mixtures were investigated in situ by means of thermoanalytical methods. Properties of sintered materials are influenced by sintering conditions such as pressure and composition of the gas phase. The influence of reactive gas components like hydrogen or oxygen on reactions during the heat treatment of hard metal mixtures (debinding, decomposition, reduction of impurities, melting ofmetal binder phase) were characterized by thermogravimetry, (TG), mass spectrometry (MS), thermodilatometry (TD), and differential scanning calorimetry (DSC) and discussed in terms ofrelevance for improving production processes. The methods oft hermal analysis, particularly thermogravimetry and evolved gas analysis as well as thermodilatometry and difference scanning calorimetry, prove to be excellent tools for creation of process knowledge for improving technical processes. Debinding and outgassing of hard metals are influenced strongly by hydrogen in comparison to vacuum or argon while sintering is only slightly influenced. The reactive properties of hydrogen cause the formation of water vapor at temperatures up to 600 deg C. This formation is due to reduction processes which take place at significant lower temperatures than in an inert atmosphere. Changes in the desorption processes due to hydrogen are also possible. The different outgassing behaviors have to be considered for the optimization of temperature-time- atmosphere-profiles. High outgassing rates require lower heating rates or soaking times. With the used analytical techniques the oxygen partial pressure is controlled at very low levels. This gives insights into the influence of atmosphere impurities (for instance through leakage). The oxygen level affects the sintering behavior only little. This unexpected finding is important for the reliability ofthe results ofthermal analysis. The investigations suggest further research directions with doped atmospheres. The investigation ofthe influence of other gas species (CO, CO2, CH4, N2) on the thermal behavior of hard rnetals may result in further optimization of sintering cycles and understanding gas reactions during the heat treatment of hard metal mixtures.