Design and chemical vapor deposition of compositionally graded coatings in the titanium-carbon-nitrogen system

The first objective was to develop methodologies for the synthesis of graded structural coatings with pre-determined composition profiles in the Ti-C-N system. The second objective was to investigate the effects of grading and of the length of the graded zone on thermal stresses at the substrate-coating interface and in the functional layer.;Monolithic coatings of TiN, TiC and TiC;Monolithic coatings of TiN and TiC grown on substrates with low coefficients of thermal expansion exhibited extensive crack networks. No cracks were observed in the coatings deposited on graphites with high coefficients of thermal expansion.;Growth rates of TiC;Stresses in the functional layer decreased with increasing length of the graded zone width when the thickness of the functional layer was small compared to that of the substrate. Stresses at the interface between the first layer of the graded zone and the substrate increased with the length of the graded zone. Stresses at the interface and in the functional layer could be minimized or made to be compressive by proper selection of the coefficient of thermal expansion of the first layer in the graded zone. (Abstract shortened with permission of author.)...