Mechanical characterization of reactively magnetron-sputtered TiN films

TiN hard coatings with thickness ranging from 1.2 to 3.5 μm were prepared by r.f. reactive magnetron-sputtering in an Ar/N2 gas mixture. Texture, residual stresses, hardness and adhesion as a function of the r.f. power and bias voltage were investigated. X-ray diffraction experiments showed a unique δ-TiN phase for all the samples. All coatings revealed residual compressive stresses, whose amplitude increased with the r.f. power up to 800 W, followed by a slight decrease. The increase in adatom mobility is the main parameter that explains this behaviour up to 800 W, whereas the decrease observed for r.f. powers above 800 W can be explained from the stress relaxation that occurs due to internal cracks resulting from the large amount of accumulated elastic stresses. Defect annihilation effect is the main parameter, which can explain the stress behaviour at higher bias voltages. The effect of ion bombardment and the defect creation at the lower negative voltages are the main parameters that explain the increase observed in stress state. Residual stresses together with the reduced grain size are the main factors that seem to control the hardness and adhesion behaviour. Differences in failure mechanisms were detected with the variation in the deposition conditions, indicating a clear influence in coating performance.