Oxidation behavior of carbon fiber-dispersed ZrB2-SiC-ZrC triple phase matrix composites in an oxyhydrogen torch environment

Abstract

We describe the fabrication of in-plane randomly oriented short carbon fiber-dispersed ZrB2-SiC (Csf/ZS) and ZrB2-SiC-ZrC (Csf/ZSZ) matrix composites with different slurry compositions using Si-melt infiltration (Si-MI). We also carried out microstructural observations, measurements of thermal conductivity, and oxyhydrogen torch oxidation tests. Microstructural characterization indicates that carbon fibers exist in the form of bundles, and these bundles are disconnected from each other. We also identify the formation of a eutectic ZrSi2 phase in the Csf/ZSZ composites during processing. The thermal conductivity of the Csf/ZSZ composites is found to be independent of the composition of the slurry and is strongly affected by the presence of the carbon fiber bundles. Post-oxidation analysis shows that the heterogeneous microstructure of the samples causes non-uniform surface oxidation. The formation of ZrO2 and SiO2, as well as of sintered monolithic ZrB2-SiC-ZrC (ZSZ) composites, was also identified. The thickness of the oxidized area in the unreacted regions of the Csf/ZSZ composites is found to be analogous to those observed in Csf/SiC and Csf/ZS composites, albeit thinner. Si and the Si-ZrSi2 eutectic phase melt during heating and they move toward the outside of specimens in oxyhydrogen torch conditions, which is a unique phenomenon never observed before in related systems.