Electrochemical and XPS studies on the passivation behavior of sputter-deposited W-Cr alloys in in 12M HCl solution

Nanocrystalline, single bcc solid solutions of W-Cr alloys have been prepared by DC magnetron sputtering over a wide composition range. The passivation behavior of these alloys was studied by electrochemical measurements, X-ray photoelectron spectroscopy (LPS) and atomic force microscopy (AFM). The W-Cr alloys are passivated spontaneously and showed significantly high corrosion resistance in 12M HCl solution at 30 degrees C. Their corrosion rates are about one order of magnitude lower than that of sputter-deposited tungsten and about five orders of magnitude lower than that of chromium metal even after prolonged immersion. XPS analysis showed that tungsten is enriched in the spontaneously passivated films formed on the alloys after long immersion time, and the passive films on the W-Cr alloys are found to be composed of double oxyhydroxide of tungsten and chromium ions. Angle-resolved XPS measurements reveal that tungsten and chromium ions are homogeneously distributed in the spontaneously passivated films. The synergistic effect of tungsten and chromium in forming the double oxyhydroxide is responsible for the higher corrosion resistance of the W-Cr alloys than of the alloy component metals. (C) 1998 Elsevier Science Ltd. All rights reserved.