CHEMICAL VAPOR-DEPOSITED INSITU COMPOSITES IN THE SYSTEM TI-SI-C

Chemical vapour deposited (CVD) SiC-ceramic composites were produced by adding TiCl4 to the SiH2Cl2-C4H10-H2 System previously used to prepare CVD beta-SiC. Experiments performed in a classical cold-wall reactor on a graphite substrate heated by Joule effect, were carried out at a constant hydrogen gas flow rate of 30 l h-1, under atmospheric pressure and at a deposition temperature ranging from 1123-1373 K. Silicon, titanium and carbon elemental compositions were determined by electron probe microanalysis-wavelength dispersive spectrometry. Phase identifications were mainly performed by Auger electron spectroscopy and X-ray diffraction and additionally by Raman spectroscopy. Three- and two-phased materials were obtained: SiC-TiC-C, SiC-TiC and SiC-TiSi2 with ratios 4 < SiC/TiC < 19 and 1.5 < SiC/TiSi2 < 11. Temperature governed the dominance of the dispersed phases: lower for TiSi2 and higher for TiC than TiC + C. At 1373 K, co-deposits were strongly textured, the beta-SiC [220] preferred orientation getting weaker as the deposition temperature decreased. Apparent crystallite size along the [220] direction decreased with temperature from about 15 nm to 10 nm. The deposition rate was almost independent of time and decreased with temperature from about 800 mum h-1 to 60 mum h-1. Arrhenius plots showed linear relationships with temperature and slope breaks at 1123 K, the temperature corresponding to the change of the dispersed phases in the SiC matrix.