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

Amorphous boron carbide (alpha-B4C) coatings were prepared on SiC substrates by chemical vapor deposition (CVD) from CH4/BCl3/H2/Ar mixtures at low temperature (900-1050 degrees 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 alpha-B4C coatings were deposited with different microstructures and phase compositions, and the effect of deposition temperature was significant. When deposited at 1000 degrees C and 1050 degrees 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 degrees C and 950 degrees 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. (c) 2008 Elsevier Ltd and Techna Group S.r.l. All rights reserved.