March 10-15, 2019
Field Assisted Sintering/Spark Plasma Sintering (FAST/SPS) is a promising technology for the energy efficient sintering of ceramic, composite and metal powders. The combination of direct current heating and applied pressure enables high heating rates, rapid densification and offers the potential to decrease the sintering temperature significantly. FAST/SPS is of special interest for materials, which are difficult to densify by conventional methods like pressure less sintering. To establish this processing technology on industrial scale, fundamental studies are required to better understand the relationship between processing parameters, specific FAST/SPS boundary conditions and resulting material properties. A challenging task – especially for non-conductive oxide ceramics – is the decrease of thermal gradients during FAST/SPS cycles to a minimum and to suppress interface reactions with the tool material.
In the present work, a systematic study was conducted in our FAST/SPS device aiming on to homogeneously densifying commercial yttria (Y2O3) powder to discs with diameter up to 100 mm. Specific attention was laid on the formation of thermal gradients during the cycle and to investigate their influence on the resulting microstructure. Therefore, different tool set ups were used. Amongst others, carbon fiber reinforced carbon (CFC) inlays were implemented to adjust thermal conductivity of the tool. Furthermore, the effect of hybrid heating was evaluated. For this experimental series, an additional induction coil was mounted in the FAST/SPS device. For evaluating the efficiency of hybrid heating, total energy consumption of the FAST/SPS device – operated with and without induction coil – was measured.
The experimental studies were accompanied by finite element modelling to estimate the temperature distribution of non-conductive yttria sample during FAST/SPS processing. The modelling results will be correlated with the grain size distribution along the cross section of the 100 mm disc. Additionally, Vickers hardness measurements were done to investigate how thermal gradients tend to influence mechanical properties.
Martin Bram, Moritz Kindelmann, Alexander M. Laptev, and Olivier Guillon, "Field assisted sintering of larger scaled ceramic parts using adapted tool design and hybrid heating" in "Electric Field Enhanced Processing of Advanced Materials II: Complexities and Opportunities", Rishi Raj, University of Colorado, USA Olivier Guillon, Forschungzentrum Jülich, Germany Hidehiro Yoshida, National Institute for Materials Science, Japan Eds, ECI Symposium Series, (2019). https://dc.engconfintl.org/efe_advancedmaterials_ii/2