Characterization of hard DC-sputtered Si-based TiN coatings: the effect of composition and ion bombardment

This work reports on the preparation and characterization of hard (Ti,Si)N nanocomposite coatings as a function of composition and ion bombardment during growth. The energy delivered to the growing film was changed using both bias voltage change and solenoid coils placed between the targets and the substrate holder. The stoichiometry of the films was investigated by Rutherford backscattering spectrometry (RBS). With reduced energy delivered to the growing film and low deposition temperatures, the coatings developed an fcc Ti 1− x Si x N y phase ( a=0.416 nm in a sample with 18 at.% of Si) where some Si atoms are probably occupying Ti positions in the TiN 1− x matrix, and can be identified as a metastable phase. With higher levels of ion irradiation, an fcc TiN phase with higher lattice parameters was developed, and a significant increase in hardness was obtained. The enhancement in species mobility at the film surface is enough to ensure an effective phase segregation, leading to the formation of an nc-TiN/a-Si 3N 4 nanocomposite. In spite of the development of some degree of residual stresses, the overall results confirm the potential benefits of ion bombardment during film growth. The fact that these high compressive stresses can be released through thermal annealing in vacuum, keeping the coating hardness values of about 45 GPa even after thermal treatments at 900 °C, is an example of these benefits.