THE CORROSION-RESISTANCE OF AL-NI ION PLATED THIN-FILMS

The Al-Ni system was investigated for possible passive film formation similar to the Al-Mg, Al-Cu, and Al-Zn systems that have previously been reported. Films of 0-100 wt% Al were coevaporated onto LN2 cooled Ebrite (Fe-26Cr-1Mo) substrates at -1.0 kV in a 3.3 Pa argon glow discharge. As-deposited film morphology, composition, and resistivity were evaluated using SEM, EDS, and a four point probe technique. Potentiodynamic polarization tests were conducted in near neutral, aerated, 3.5% NaCl at room temperature. Some of these tests were terminated prematurely for morphological examination of the film surface. The corrosion resistance of the Al-Ni alloy films was found to increase with Ni content, with high wt% Ni films showing extended regions of stability. In addition, the Ni films were superior to pure bulk (99.8%) Ni, with protection ranges of 0.8 and 0.2 V, respectively, when scanned anodically. Corrosion product film formation was observed for alloy films of higher Ni content, but the products broke down quickly. The enhanced protection of the thin Ni films might be due to the ion plated film structure.