Influence of the energy parameter on the microstructure of chromium nitride coatings

Increasingly, chromium nitride (CrNx) coatings are used as a replacement for titanium nitride coatings and electroplated hard chromium in various applications. This work reports an investigation of chromium nitride coatings deposited using unbalanced magnetron sputtering. The plasma characteristics as a function of the target–substrate distance were evaluated by means of Langmuir probes. Samples of CrNx were deposited at different ion energies and ion-current densities. Other deposition conditions, such as substrate temperature, pressure and target power, were kept constant. The microstructure and composition were analyzed by means of X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and Rutherford back-scattering spectrometry, respectively. The results are analyzed in terms of the energy parameter (Ep), which combines both the ion energy and ion flux. The nitrogen to chromium ratio (N/Cr ≈ 1) and the microhardness (∼ 20 GPa) were nearly constant for all samples, although the energy parameter varied from 10 to 320 eV/atom. On the other hand, the microstructure varied from columns separated to a dense fibrous microstructure with almost equiaxed grains. Films deposited at low Ep values presented about 80% of (200) orientation and 20% (111) and (220), whereas at higher Ep values the orientation was completely (200).