Microstructure and deposition mechanism of CVD amorphous boron carbide coatings deposited on SiC substrates at low temperature

Amorphous boron carbide (α-B₄C) coatings were prepared on SiC substrates by chemical vapor deposition (CVD) from CH₄/BCl₃/H₂/Ar mixtures at low temperature (900-1050 °C) and reduced pressure (10 kPa). The deposited coatings were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-Raman spectroscopy, energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results showed that two kinds of α-B₄C coatings were deposited with different microstructures and phase compositions, and the effect of deposition temperature was significant. When deposited at 1000 °C and 1050 °C, the coatings exhibited a nodular morphology and had a relatively low content of boron. The free carbon was distributed in them inhomogeneously; in contrast, when deposited at 900 °C and 950 °C, the coatings presented a comparatively flat morphology and had a uniform internal structure and high boron content. They did not contain free carbon. At the last of this paper, the pertinent mechanisms resulting in differences in microstructure and phase composition were discussed.