Oxidation behavior of TiCxN1−x coatings as a function of C/N ratio

Titanium nitride, carbide and carbonitride coatings were synthesized on titanium substrates by the thermochemical diffusion process in ammonia, methane and varying compositions of ammonia/methane mixture, respectively. High temperature oxidation resistance of these coatings has been studied as a function of carbon to nitrogen ratio in the coatings. Oxidation experiments were conducted in a thermogravimetric analyzer in oxygen atmosphere at 800 °C. XRD, SEM, EDS, XPS and Raman measurements before and after the oxidation studies revealed that the content of sp3 bonded carbon interspersed in the coatings plays a key role in deciding the oxidation resistance of the coatings. TiC with higher sp3 carbon showed maximum oxidation resistance and TiN the least. Incorporation of even a small amount of N in TiC and C in TiN is found to drastically alter their oxidation resistance.