On the phase evolution during reaction of molten Si 0.9 Zr 0.1 and Si 0.9 Hf 0.1 alloys with carbon

Ceramics and ceramic matrix composites (CMCs) produced by melt infiltration have emerged as commercially important components in advanced friction (e.g., brake rotors), propulsion (e.g., turbine engine and rocket motor parts), and optical (e.g., mirrors) applications. The use of alloyed silicon infiltrants provides an attractive means to adjust composite composition, structure, and properties via relatively straightforward processing changes. In the present work, the effects of alloying silicon with hafnium or zirconium on the phase evolution in the reactions between C and Si alloys are investigated. A diffusion couple configuration is used to study reactions in Si(l) + C, Si 0.90 Zr 0.10 (l) + C, and Si 0.90 Hf 0.10 (l) + C systems at 1450 °C. The Si 0.90 Zr 0.10 (l) − C system was found to evolve in a similar manner as the Si(l) − C system, forming SiC at the diffusion couple interface. This Zr-containing system was determined to form an additional mixed Zr, Si, C phase that causes a slight decrease in the overall rate of SiC when compared to Si–C system. The Si 0.90 Hf 0.10 (l) − C system exhibited behavior distinct from the phase evolution witnessed in the reaction of carbon with pure Si or Zr-containing Si alloys. Initial SiC formation at the interface in the Si 0.90 Hf 0.10 (l) − C system is found to enrich the Hf content of the melt enough to promote the formation of a HfC layer at the Si 0.90 Hf 0.10 (l) − C interface. This HfC layer then acts as a barrier that hinders further SiC growth, resulting in significantly reduced SiC formation kinetics when compared to the Si(l) − C and Si 0.90 Zr 0.10 (l) − C systems. The results of this fundamental study pose clear indications for the generation of SiC-based ceramic composites with refractory-containing Si-based melts.