Microstructure and mechanical properties of Cu doped TiN superhard nanocomposite coatings

Ti–Cu–N nanocomposite films with various copper contents were deposited by simultaneous co-deposition of titanium nitride and copper using a reactive arc ion plating and magnetron sputtering hybrid system. The structure and mechanical properties of these films were found to be dependent on the copper concentration. X-ray diffraction analysis and high resolution and conventional transmission electron microscopy analysis showed that the grain size in films decreases with increasing the copper content while no sign of copper phase was observed. Ti–Cu–N films containing 1.5 at.% of copper exhibited maximum hardness of 45 GPa and relatively low friction coefficient of 0.3. The further increase of copper content in the film resulted in sharp decrease of hardness. The obtained results are discussed with the model of film growth in the presence of impurities as related to the concept for the design of superhard nanocomposite materials. The role of soft metallic phase in two-phase composite materials containing one hard and one soft phase is also discussed.