Mechanical and tribological properties of CrN/TiN superlattice coatings deposited by a combination of arc-free deep oscillation magnetron sputtering with pulsed dc magnetron sputtering

Abstract

Deep oscillation magnetron sputtering (DOMS) is an alternative high-power pulsed magnetron sputtering technique, which offers virtually arc-free depositions especially for reactive depositions of some insulating coatings under optimized pulsing conditions. CrN/TiN superlattice coatings with a modulated period (Λ) ranging from 5.7 to 10.2nm were deposited using a combination of DOMS and pulsed dc magnetron sputtering in a closed field unbalanced magnetron sputtering system. As a Λ was increased from 5.7 to 10.2nm, CrN/TiN superlattice coatings with the increased Cr/(Cr+Ti) ratio from 0.177 to 0.496 exhibited a single phase face-centered cubic structure with a strong {111} texture. Correspondingly, the hardness, the H/E* and H3/E*2 ratios showed an initial increase, followed by a decrease. The coatings at Λ=6.3nm with the Cr/(Cr+Ti) ratio of 0.294 and fine grain size of about 30nm showed the highest hardness of 36GPa, H/E* ratio of 0.093 and H3/E*2 ratio of 0.313. It also showed a mild abrasive wear with the lowest friction coefficient and specific wear rate of 0.27 and 0.5×10−6mm3N−1m−1, respectively. With increasing Λ, the friction coefficient and specific wear rate decreased and then increased. The dominant wear mechanism changed from oxidative wear to mild abrasive wear, and then to severe oxidative wear. The changes of H, H/E* and H3/E*2 ratios and adhesion of CrN/TiN superlattice coatings resulted in variation of tribological properties and wear mechanism.