Effect of coating architectures on the wear and hydrophobic properties of Al–N/Cr–N multilayer coatings

Abstract

Two coating architectures with various deposition times (Dts) for each layer and N2 gas flow rate ratio η (N2/(N2+Ar)) of Al–N/Cr–N multilayer coatings were prepared using unbalanced magnetron reactive sputtering. Using the same coating process, two coating architectures were deposited on the high speed tool steel and Si wafer, one starting with an Al–N layer designed as the Al–N/Cr–N/…/Cr–N/Al–N (architecture A) and the other starting with a Cr–N layer designed as the Cr–N/Al–N/…/Al–N/Cr–N (architecture C). During the coating process, the N2 gas flow rate ratio η was set at 15%, 20% and 25% to control the Cr–N and Al–N layer phases. This study investigates the effects of architectures, Dt and η on the wear and hydrophobic properties of the coatings. The X-ray diffraction results show that Cr(N), Cr(N)+Cr2N and Cr2N+CrN phases respectively form in the Cr–N layer given η=15%, 20% and 25%, and only the hcp-AlN phase forms in the Al–N layer. The layer thickness ratio (λ) of the Cr–N layer to the Al–N layer increases from 2.7 to 6.4 as η increases from 15 to 25%. The wear resistance of the coatings is strongly related to the coating architecture. The architecture A coatings exhibit better wear resistance than the architecture C coatings. The number of layers and layer thickness ratios λ also affects the wear behavior. In terms of the hydrophobic property, the coating architecture C with the Cr2N+CrN phase (η=25%) on the top layer shows higher water contact angle measurements of 95°–97°.