Boron-SiC Diffusion Couple: Thermodynamics and Reactivity at High Temperature

Abstract

This study investigates the reaction between silicon carbide (SiC) and boron (B) at high temperature. A B/SiC diffusion couple treated at 1973 K (1700 °C) for 8 h under uniaxial pressure was analyzed using energy dispersive spectroscopy and electron probe microanalysis with wavelength dispersive spectroscopy. Distinct reaction zones were identified, and the reaction sequence was established as SiC/(B_xC)/SiB₆/(SiB_n)/(β-B). This sequence aligns with B-C-Si phase equilibria and driving force calculations, which predict (B_xC) as the first phase formed between B and SiC. The formation of ternary solid solutions is also discussed, comparing reported Si solubility in (B_xC) and B solubility in SiC with our findings. The boron carbide layer exhibits a composition gradient (13.7 at% C to 12.4 at% C) and was identified as a ternary solution with an average silicon content of 2.0 at%. This study is based on an unprecedented approach to interface reactivity in the B-C-Si system, relying on the experimental study of the B-SiC diffusion couple and thermodynamic calculations of phase equilibria. The results also highlight the relevance of the existing thermodynamic database for predicting phase equilibria in this system. However, the composition range of (B_xC) and (SiB_n) may require further investigation.