MICROSTRUCTURE OF CHEMICALLY VAPOR CODEPOSITED SIC-TIC-C NANOCOMPOSITES

SiC-TiC-C nanocomposites were chemically vapour codeposited onto a graphite substrate under atmospheric pressure, in the temperature range 950-1150-degrees-C, using the TiCl4-C4H10-SiH2Cl2-H2 gas system. SiC, TiC and excess carbon molar compositions were calculated using determination by electron probe microanalysis-wavelength-dispersive spectroscopy of the atomic percentages of Si, Ti and C after having identified SiC and TiC by Auger electron spectroscopy. The [220] preferential orientation corresponding to beta-SiC + cubic TiC, revealed by X-ray diffraction, decreased with deposition temperature and almost no texture remained at 1050-degrees-C. The apparent crystallite size along the [220] direction was about 10-20 nm. Micro-Raman spectra showed that the Raman size of the excess carbon did not exceed a few nanometres and that TiC and SiC were structurally disordered. Using transmission and high resolution electron microscopies, codeposits were found to consist of needles of SiC + TiC embedded in a poorly crystallized SiC matrix. They were stacking faulted and 10-15 nm broad. The needles were predominantly [220] oriented perpendicular to the substrate, whereas secondary needles were growing in {111} planes with [112] average direction.