Physical and Tribological Proprieties of RF Sputtered Chromium Aluminum Nitrides Coatings

Super hard coatings have been applied to increase the lifetime and to improve the efficiency of machining tools for drilling, cutting, and molding. [1] For this, physical vapor deposition (PVD) method is mostly applied. They have been reported to increase the abrasive wear resistance and to increase the economical benefits of coated materials. [2-4]. In the present study, a nanostructured Cr-Al-N thin film with different Al content (0 to 50 at.%) have been deposited using radio-frequency (R.F) reactive magnetron sputtering system on Si (100) wafer and XC100 steel substrate without heating. The structural evolution and morphological changes as a function of the Zr content were performed using XRD, (EDS, WDS), WPS, XPS, SEM, AFM, Nanoindentation, Scratch adhesion. The tribological performances were evaluated using a ball-on-disk type Oscillating tribometer. The tests were carried out under normal loads of 2, 4 and 6 N respectively, with an alumina ball (Al 2 O 3 ) as a counter face. Different concentrations of Aluminium (Al) (0 – 50 at.%) were studied. The results show, that, with increasing Al content, the film structure changed with the coexistence of (Cr-N, Al-N) crystallographic orientation mixture. The films formed a (Cr, Al) N solid solution where Al atoms substitute Cr atoms, The crystallite size of the CrAlN system was reduced to 10.8 nm at 31.8 at.% Aluminium content. CrN Lattice parameter increased from 4.17 to 4.32 A with the crystallite size refinement. Morphological studies of the films showed that the roughness continuously decreased with increasing zirconium content, exhibiting a value of 11.2 nm at 31.8 at.% Aluminium. The mechanical parameters (H, σ, E, H/E and H3/E2) were significantly improved in comparison to binary films, especially at 30 at. % Al. The friction and wear rate tends to decrease with increasing zirconium content, reaching the lowest value of 1.95 × 10−2 µm3/(N.µm) at 31.8 at.% zirconium. The sliding wear rate and coefficient of friction were lower in the samples with 31.8 at.% zirconium content. The improved friction and wear resistance were attributed to the grain refinement strengthening mechanism at 31.8 at.% of zirconium.