GROWTH AND STRUCTURE OF TIC COATINGS CHEMICALLY VAPOR-DEPOSITED ON GRAPHITE SUBSTRATES

Abstract

TIC coatings were grown on graphite substrates by the chemical vapour deposition technique, using gas mixtures of CH4-TICl4-H-2 at a total pressure of 10.7 kPa and at temperatures of 1400 and 1425 K. The growth rate and structure of the TIC coatings were investigated as a function of CH4 and H-2 concentrations. The deposition rate of TiC increased with increasing CH4 flow rate, but did not change with H-2 flow rate. This behaviour was explained by a mass transport theory. Thermodynamic analyses based on minimization of Gibbs' free energy predicted carbon codeposition with TiC. X-ray diffraction and Auger electron spectroscopy (AES) studies and microstructural observations, however, suggested that free carbon did not form. Textural analyses indicated that the growth of TIC coatings was initiated as randomly oriented crystallites, and as the thickness of the coatings increased, preferentially oriented columnar grains developed. The textures of TiC coatings with the same thickness changed from the [110] orientation to the [100] orientation with decreasing H-2 flow rate for a constant CH4 flow rate. The CH4 concentration also greatly influenced the preferred orientation of the coatings.