Synthese von Cr$_{2}$AIC MAX-Phasen Kompositen und Bestimmung ihrer oxidativen Eigenschaften

Go, Teresa; Gonzalez-Julian, Jesus (Thesis advisor); Schneider, Jochen M. (Thesis advisor)

Jülich : Forschungszentrum Jülich GmbH, Zentralbibliothek, Verlag (2021)
Book, Dissertation / PhD Thesis

In: Schriften des Forschungszentrums Jülich. Reihe Energie & Umwelt = energy & environment 558
Page(s)/Article-Nr.: ii, 119 Seiten : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2021

Abstract

Three different ceramic matrix composites (CMCs) were produced using Cr2AlC as a matrix, and carbon, SiC, and Al2O3 short fibers as a secondary phase. Cr2AlC powders were synthe-sized by solid-state reaction, followed by mixing with the fibers, and full densification using a field-assisted sintering technique (FAST/SPS). Carbon fibers react strongly with Cr2AlC, meaning that these composites are not suitable for use, while the reaction of SiC fibers is less strong. The composites containing alumina fibers do not exhibit any reaction. Oxidation tests of the monolithic Cr2AlC and the composites were performed by thermogravimetric analysis. Of all the chosen CMCs, 10 wt.% SiC fibers resulted in the lowest mass gain. The parabolic and cubic rates of oxidation were determined to find the best fitting calculation. The overall oxidation response is parabolic. The alumina layer formed at 1000 °C is well attached and the oxidation response is good. However, at 1200 °C, this layer detached for monolithic material and 10 wt.% Al2O3 fibers. In long-term oxidation tests at 1200 °C for 4 weeks, a strong reac-tion of the CMCs in contrast to the monolithic material is observed. The oxidation response of the alumina fiber CMC is good under realistic conditions using a burner rig for cyclic oxida-tion, as defects or degradation are barely visible, and the alumina layer is well attached. The mechanical reinforcement effect of the fibers was implemented by measuring the compres-sive strength at room temperature and 900 °C. This reinforcement is clearly evident here. CMCs with Al2O3-fibers withstand higher compressive stresses than monolithic material. The highest compressive stresses are measured in CMCs with SiC fibers, whereby the reason for this increase can also lie in the secondary phases that arise during sintering.

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