Mechanical and tribological properties of compositionally graded CrAlN films deposited by AC reactive magnetron sputtering

In this work, CrAlN films with Al/Cr atomic ratios between 0.02 and 1.4 were deposited on tool inserts by AC magnetron sputtering at 5 kW for three different Ar/N2 flow rates. The unique configuration of the inverted cylindrical magnetron sputtering (ICM-10) system enables the deposition of compositionally graded Cr–Al–N coatings under a single deposition condition. The effect of aluminum on the structural, mechanical and tribological properties of (Cr,Al)N coatings are reported and compared with ALCRONA and CrN coatings from Balzers. Mechanical properties have been evaluated by the microhardness indentation technique, and the hardness is 18 and 15 GPa for CrN and CrAlN films, respectively. The tribological tests have been performed using the pin-on-disc method at room temperature and 700 °C. The results indicate that the coefficient of friction at room temperature and 700 °C for all the deposited coatings, Balzers-ALCRONA and CrN fall between 0.4–0.6. The wear volume at high temperature (700 °C) decreases with increase in Al incorporation. Auger Electron Spectroscopy reveals that all films have about 10 at.% of oxygen. Atomic Force Microscopy showed that our films had roughness ranging from 80 to 150 nm. X-ray mapping on (Cr, Al)N coatings for different Ar/N2 gas compositions showed transitions from cubic to hexagonal with decreasing nitrogen.