In-situ-Messung und Simulation der Flüssigphasensilicierung

Hofbauer, Peter Josef GND

Die Infiltration von porösen Kohlenstoffvorformen mit flüssigem Silicium ist eine der wirtschaftlichsten Technologien zur Herstellung von kohlenstofffaserverstärktem Siliciumcarbid. Trotz jahrzehntelanger Forschung sind die physikalischen Phänomene an der Infiltrationsfront noch nicht hinreichend verstanden worden. Die vorliegende Arbeit dient dazu, diese Forschungslücken zu schließen. Hierzu befasst sie sich zunächst mit den bisher bekannten Infiltrationsmodellen. Anschließend wird ein neuartiger Versuchsaufbau vorgestellt, der eine In-situ-Beobachtung einer Spaltkapillare aus Glaskohlenstoff während der Siliciuminfiltration ermöglicht. Die Versuche zeigten, dass sich die Infiltrationskinetik grundlegend von den Vorhersagen der bekannten Infiltrationsmodelle unterscheidet. Abschließend wird der Aufbau eines numerischen Modells erläutert, das erstmals die reaktive Infiltration der Kohlenstoffvorformen im Dreidimensionalen simuliert. Dabei führen eine neue Infiltrationsgleichung und ein zeitabhängiger Diffusionskoeffizient zu einer guten Übereinstimmung von Simulations- und Messergebnisse.

The liquid phase infiltration of porous carbon preforms with silicon, commonly referred to as Liquid Silicon Infiltration (LSI), is one of the most economical technologies for the production of carbon fiber reinforced silicon carbide (C/SiC). Despite decades of research, the physical phenomena on the infiltration front have not yet been sufficiently understood. Consequently, up to now there is no mechanistic model of the reactive infiltration process that could help to optimize the production process of C/SiC components. The present work serves to close the research gaps and provide a validated simulation model for process optimization. The present study was divided into three parts, with the first part initially dealing with the manufacturing processes of C/SiC components. Subsequently, the basic chemical and physical processes of the reaction of silicon and carbon to silicon carbide are explained. Followed by the previous understanding of the infiltration of porous carbon fiber reinforced carbon preforms (C/C-Preforms) with liquid silicon, the state of the art will be dealt with using the existing infiltration and diffusion models. The second part deals with the investigation of the LSI process by a newly developed experimental setup. This enables in situ observation during the infiltration of a gap capillary of glassy carbon with silicon. Originally, the experimental setup was intended to validate the previously recognized infiltration models based on general capillary theory. However, the experiments showed that the infiltration kinetics fundamentally differ from the behavior predicted by the known infiltration models. Further investigations led to new findings, which enabled the development of a mesoscopic model for predicting the actual infiltration behavior. With the infiltration and investigation of porous C/C materials, the scope of the infiltration model is extended to commercial C/C materials. The third and last part deals with the structure of a numerical model for the simulation of the LSI process. The calculation model, based on the finite element method, includes both infiltration and reaction kinetics. For the first time, the reactive infiltration of porous C/C preforms was simulated in three dimensions and the model was validated with in situ measurements. A newly developed infiltration equation and the introduction of a time-dependent diffusion coefficient led to a good agreement between simulation and measurement results as well as to short computation times even for complex components on an industrial scale.

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Hofbauer, P.J., 2020. In-situ-Messung und Simulation der Flüssigphasensilicierung. Werkstofftechnik aktuell. Universitätsverlag Ilmenau, Ilmenau. https://doi.org/10.22032/dbt.45029
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