Role of Minor Alloying Elements in the Corrosion of Selected Amorphous Alloys

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TECHNICAL SUMMARY:Traditional methods to obtain excellent corrosion resistance in metallic alloys include addition of metallic and metalloid elements up to the concentrations necessary to either form passivating films, inhibit active dissolution in pits, or reach the ?parting limit? associated with dealloying. Structural and chemical defects have also been affected by controlled alloying additions in heterogeneous materials. Amorphous metals incorporate many of these strategies: structural and chemical heterogeneities are minimized, and metastable supersaturated solid solutions are often formed with large concentrations of beneficial alloying elements. However, the possible beneficial role(s) of minor alloying additions on corrosion resistance are rarely explored. Yet, minor alloying elements offer substantial opportunities to improve the corrosion resistance of many metallic materials. Indeed, this strategy has provided some of the greatest gains in alloy corrosion resistance in the last 100 years. This work will investigate the role of trace beneficial alloying additions in two solid solution systems: amorphous Fe-Cr-Mo-C alloys containing small concentrations of B, Y, W and Si as well as in Al-Cu-Mg alloys containing small amounts of Ni or Pd through systematic additions and nano- as well as micro-meter scale characterization and modeling. Several testable hypotheses exist; some of these will be explored in the proposed work. Minor alloying elements can affect bonding and/or form atomic clusters in the alloy with less noble, corrosion prone alloying elements to alter their otherwise preferential oxidation tendency. High melting temperature, noble minor alloying elements lack surface mobility and these relatively immobile species could block dissolution sites on the surface of dissolving metals. Minor alloying elements could also alter the solute diffusion rates in the oxide or alloy, thus operating as agents that shift alloying element ratios favorably for corrosion resistance.NON-TECHNICAL SUMMARY:Corrosion of engineering materials is an issue of international importance that threatens safety, health, security, needs for clean water and energy independence. The annual cost in the US exceeds 300 billion dollars per year. There is also a growing shortage of newly trained corrosion scientists and engineers connected with the national shortage of engineering graduates. This project not only supports the fundamental understanding necessary for development of enhanced alloys for security and energy applications but also supports human resource development in the area of corrosion science ? a crucial need identified by the National Academy of Sciences. This project provides the venue for the multi-disciplinary knowledge-based education of 2 graduate students in Materials Science and Engineering that will then provide needed professionals in the corrosion-metallurgy field. The Center for Electrochemical Science and Engineering at the University of Virginia trains students in the multi-disciplinary areas of corrosion and materials science/engineering and is a major supplier of professionals with such knowledge to US industry, government, and academia. Under-represented gender and ethnic students are a proven prior and on-going emphasis of this integrated training and research endeavor. Students disseminate scientific results in broad interest papers and books, specialty papers, conferences, short courses and lab tours/demos for K-12 students.