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.
Corrosion of metallic engineered materials cost the US over 300 billion dollars per year and may cost the DOD 30 billion dollars in direct costs each year. Corrosion presents a small or large part of the technical hurdle to e overcomes to achieve success in nearly every great engineering "grand challenge" identified in a recent National Academy report such as the quest for clean abundant energy, the need for clean water or the need for improved civil infrastructure. There is also the loss of life due to engineering failures related to corrosion. To improve corrosion resistance or even "schedule designed corrosive phenomena" such as anti-microbial copper function, or biodegradable stents, corrosion science must move beyond the trial and error and lesson learned approaches. Traditional methods to obtain excellent corrosion resistance in single phase, solid solution alloys include addition of transition or refractory metal 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 controlled 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 in multi-component alloys are rarely explored. Yet, minor alloying elements offer substantial opportunities to improve the corrosion resistance of many metallic materials and is receiving growing attention. Indeed, this strategy has provided some of the greatest gains in alloy corrosion resistance in the last 100 years. This proposal investigated the role of trace beneficial alloying additions in several "model" solid solution alloy systems. This NSF work describes research to clarify the mechanism by which minor elements improve corrosion properties. The corrosion properties discovered were connected with atomic scale measurements of fundamental properties to test selected hypotheses. The role(s) of minor elements on near-surface alloying element ratios were investigated by using state of the art measurement tools. The formation of atomic clusters and changes in coordination number, bond length and bond strength were examined after systematic additions of alloying additions to relate atomic structure with macro-corrosion phenomena for one of the first times. In addition the role of solid solution structure (amorphous as quenched versus relaxed amorphous; or ordered vs. disordered crystalline, or amorphous versus ordered crystalline solid solution) and, where appropriate, crystal orientation effects were studied. The results of the work lead to over 9 archival publications in leading peer reviewed journals, several Ph.D. thesis dissertations. Intellectual merits include creation of new understandings of the role of minor and trace alloying elements on solid solution alloy corrosion at the nm-scale in several generic classes of materials (i.e., Fe- Cu and Al-based), and guidance toward design of new corrosion resistant alloys. Design of more corrosion resistant materials will be enabled. The most important broader impact included the education of numerous students ranging from high school, undergraduates, graduate students, and post—docs. Ph.D. candidates were trained in fundamentals of metallurgy, surface science, electrochemistry and corrosion. They were also trained in science ethics, experimental design, data collection and analysis, interpretation, report and paper writing and reviewing, the ability to identify needs, gaps and opportunities in science topics via literature review and team work/communications written/oral. Undergraduates receive basic training in materials science, specimen preparation and electrochemistry applied to materials science. Over five women science and engineering major were engaged in the research. Most now flourish in science or engineering related fields. This contributed to the human resources science infrastructure of the US and scientific human resource diversity as well as creating opportunities in science for a broad range of the US population including color, economic and gender diversity.
