Influence of the ion–atom flux ratio on the mechanical properties of chromium nitride thin films

In this paper we report the mechanical properties of chromium nitride (CrN) thin films deposited at different levels of ion bombardment and their relationship with the microstructural parameters, such as grain size, preferred orientation and residual stress. The samples were deposited by unbalanced magnetron sputtering changing the substrate–target distance and the substrate bias, keeping other deposition condition fixed. The mechanical properties were obtained by nanoindentation performed on 1.8 μm thick samples. Under the different deposition conditions all of the CrN films were approximately stoichiometric, but clear variations in the microstructure were seen. The hardness was nearly constant at 24–27 GPa even when the grain size, residual stress and crystalline orientation changed. However, the elastic modulus showed a steady increase from 300 to 350 GPa, proportional to the variations in grain size and the residual stress level.