Vapor‐mediated melt infiltration for synthesizing SiC composite matrices

Abstract

A two-step synthesis of SiC involving initial exposure of carbon surfaces to Si vapor, followed by Si melt infiltration, is investigated in this article with emphases on the mechanisms, kinetics, and microstructure evolution. Interrupted differential thermal analysis of amorphous C and Si powder mixtures and microstructure characterization are used to generate insight into the stages of the reaction. Exposure to Si vapor yields a SiC layer with nano-scale porosity driven by the volume change associated with the reaction. This forms a continuous pore network that promotes subsequent melt access to the reaction front with the C. While the pores remain open, the vapor phase reaction proceeds at a nearly constant rate and exhibits a strong temperature sensitivity, the latter due in part to the temperature sensitivity of the Si vapor pressure. The implications for enhancing the reactive melt infiltration process and fabrication of SiC matrices for ceramic composites are discussed.

Influence of pyrolysis and Silicon infiltration on the properties of CMC parts shaped by composite flow molding

“…Region F is characterized by SiC crystals formed by the precipitation of SiC in the molten Si, indicating that carbon atoms diffused in molten Si during processing 24 . This kind of reaction is most likely happening in the regions where pyrolytic (and thus amorphous) carbon is present 25 . Finally region G shows the formation of thin SiC layer around the carbon fibers which is due to the concomitant spreading of Si vapors into the preforms 23,25 …”

“…25 Finally region G shows the formation of thin SiC layer around the carbon fibers which is due to the concomitant spreading of Si vapors into the preforms. 23,25 Figure 4 shows the micrographs of the samples processed according the experimental plan of Table 2. They show that the samples infiltrated at low temperature (Figure 4A,C,E,G) present regions with dense SiC adhering to the preforms inner surface.…”

“…24 This kind of reaction is most likely happening in the regions where pyrolytic (and thus amorphous) carbon is present. 25 Finally region G shows the formation of thin SiC layer around the carbon fibers which is due to the concomitant spreading of Si vapors into the preforms. 23,25 Figure 4 shows the micrographs of the samples processed according the experimental plan of Table 2.…”

Microstructural characterization of ZrB2–SiC–Si–MoSi2–WC coatings applied by SPS on graphite substrate

“…In this interface, up to a specific depth of the graphite substrate, a difference in the graphite substrate microstructure is seen, which may be related to the penetration of silicon in the substrate. Considering that the melting point of silicon is 1440 °C [32] and on the other hand, the temperature of the SPS process (1875 °C) is higher than its melting point, the silicon in the primary powder mixture melts and gradually penetrates into the graphite substrate through the pores due to the capillary force and the applied pressure during the SPS process [25,26]. Therefore, because of the penetration of silicon in the microstructure of the graphite substrate and the availability of environmental conditions (atmosphere, pressure, and temperature), it is feasible to form an infiltration SiC-C layer as a result of the reaction between Si and the C of the graphite substrate.…”