Microstructure, mechanical and corrosion behavior of CrNx/Al2O3 multilayer films deposited by magnetron sputtering

A novel design was adopted to improve corrosion resistance of 2024 Al alloys by magnetron sputtering CrNx based multilayer films with Al2O3 intercalation. The multilayer films were composed of inhomogeneous structure, i.e., thick CrNx transition layer (similar to 2 mu m) + CrNx/Al2O3 multilayer (similar to 1 mu m). The effect of Al2O3 interlayer and modulation period on microstructure and performance of multilayer films were investigated. The nitride layer was dominated by Cr2N and CrN with minor Cr, while the Al2O3 layer displayed in the amorphous form. The intercalation of Al2O3 blocked the columnar growth in CrNx layers and refined the grains. As the period increased, the cluster particle size decreased and the mechanical properties increased, with the maximum hardness and modulus at CN-8 (19.13 GPa and 282.2 GPa). In addition, the multilayer structure enhanced the bonding between the film and the substrate, and has an improvement on the hard and brittle properties of the film. The multilayer films showed improved corrosion resistance than the CrNx mono-layer in 3.5 wt% NaCl solution. The film with CrNx-top layer showed superior corrosion resistance than the film with Al2O3-top layer. The increasing period also enhanced corrosion resistance, showing an excellent corrosion potential and corrosion current density (E-corr=-0.538 V, i(corr)=0.96 mu A.cm(-2)) at CN-8.