Structure, mechanical and tribological properties of carbon nitride-based superlattice and titanium diboride-based composite films synthesized by magnetron sputtering.

摘要

This thesis is focused on the synthesis of hard, adherent and smooth thin films using magnetron sputtering. The materials investigated in this research include carbon nitride (CN_x) based superlattice and titanium diboride (TiB₂) based composite thin films. Different techniques were used to characterize the films in terms of composition, structure, bonding configuration, mechanical and tribological properties.; The basic premise of the pseudomorphic growth model of the CN_x/ZrN superlattice system is that ZrN (111) provides a good lattice match and similar symmetry to β-C3N4 (0001). β-C3N4 was predicted to have mechanical properties similar to those of diamond. Under optimum process conditions, the CN_x/ZrN superlattice coatings are dense and fully crystalline with maximum hardness of 40–45 GPa. The effect of the process parameters on the structure and mechanical properties of the resultant coatings is discussed. RBS simulation shows that the carbon to nitrogen ratio in the CN_x layers is close to 3:4. Structure and hardness studies demonstrate a strong correlation between the coating hardness and the ZrN(111) texture, and CN _x and ZrN play a synergistic role in improved crystalline growth. High resolution electron microscopy shows that the carbon nitride regions are more crystalline with decreasing periods, and the diffraction studies reveal three new d-spacings which cannot be accounted for by ZrN but can be indexed to three reflections from α-C₃N₄ or β-C ₃N₄. Chemical bonding studies show that the carbon is primarily in the sp3 configuration in the superlattice coatings with a small period of $\sim$2nm. The CN_x/Zr coatings are ultra smooth, and have relatively low friction coefficient and wear coefficient.; In TiB₂ related work, both conventional and ionized magnetron sputtering were used to study the effect of ion energy and ion flux on the properties of the monolithic TB₂ coatings. Attempts to enhance the hardness of the TB₂ coatings by doping with nitrogen or carbon, and by synthesizing CN_x/TB₂ superlattice coatings are also presented. Incorporation of nitrogen or carbon into TiB₂ coatings causes a decrease in the hardness of the coatings.