In the past, it has been suggested that a solute-rich layer at the oxide/metal interface was responsible for the significantly enhanced passivity of nonequilibrium Al-Mo and Al-W alloys in comparison to pure aluminum. X-ray photoelectron spectroscopy. Auger electron spectroscopy, and transmission electron microscopy were used in this research to characterize and quantify the oxide chemistry and oxide/metal interface of nonequilibrium Al-Mo and Al-W alloys as a function of electrochemical polarization in chloride-containing solutions and gain further insight into the mechanism responsible for the enhanced passivity. The alloys evaluated in this study were prepared by magnetron co-sputter deposition, and the chloride solutions used in the experiments were either near- neutral pH or moderately acidic (pH 2 and pH 3). A solute- enriched layer was not identified in the neutral pH environment. However, each of the surface analytical methods provided evidence of the presence of solute enrichment after anodic polarization in the moderately acidic solutions. Since corrosion of aluminum alloys is typically localized in chloride-containing environments and since these sites exhibit low pH values, the presence of an enriched layer at low pH is of particular interest. A repassivation mechanism incorporating the solute-enriched metallic layer at the oxide/metal interface is proposed to account for a component of the marked enhancement of the localized corrosion resistance observed in the Al-W and Al-Mo systems, relative to commercial aluminum alloys. Following oxide breakdown, preferential dissolution of aluminum occurs in the occluded environment of the incipient pit. The solute-enriched oxide/metal interface facilitates reduction in the dissolution kinetics at the growth front and encourages repassivation through formation of a solute-rich oxide.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Materials Science(all)