Corrosion Mechanisms in Amorphous Alloys: Critical Compositional and Structural Defects for Local Corrosion

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TECHNICAL: The outstanding local corrosion resistance and excellent passivity of amorphous metallic materials is often attributed to the elimination of microstructural heterogeneity. However, identification of the exact governing critical defect is lacking and competing explanations exist. In both traditional glass materials as well as newer bulk metallic glass alloys, this generic question concerning the fundamental origins of excellent corrosion resistance remain unresolved. As long as the mechanism is unclear, the impacts of partial devitrification on corrosion cannot be forecast. In this regard, there are a number of unresolved issues and he opportunity exists to clarify these issues through careful selection of model alloys that enable rejection or acceptance of each hypothesis for corrosion resistance. Regarding the critical flaw size, selected amorphous alloys can be partially devitrified by primary crystallization to form isolated solute rich and/or solute lean crystals in a remaining solute rich amorphous matrix which serve as model materials that enable exploration of a range of non-uniformities. The mechanism for good corrosion resistance when a non-uniformity is below the critical size will be determined in complimentary multidisciplinary studies. Several testable hypotheses for the good corrosion resistance of small nonuniformities in an amorphous matrix will be explored. Regarding the need to separate the roles of structural from compositional non-uniformities, the opportunity exists to explore this issue through selection of alloys which undergo devitrification without change in composition. For example, certain Fe- B, Co-B, Cu-Zr and Al-Sm amorphous alloys can devitrify by polymorphous crystallization to form crystalline solid solutions of the same composition. In addition, , origins of corrosion of the heat-treated amorphous matrix will be studied focusing on the role(s) of structural and compositional relaxation of the amorphous phase in nano-scale roughening by corrosive dissolution. NON-TECHNICAL: Broader implications include human resource development. The CESE trains students in the multidisciplinary area of corrosion, materials science/engineering and surface science and is a major supplier of materials professionals with corrosion knowledge to US industry, government and academia. Under represented gender and ethnic students have and will continue to be a focus of integrated training and research endeavor on this grant. Integration of research and education is accomplished at UVA through dual role of research from NSF supported activities in both theses/degrees and for external publication, presentation and knowledge creation/dissemination. Students, as well as the PI, disseminate results in broad interest papers, specialty papers, conferences, and lab tours/demos for K-12 students.