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THE role of atomic scale structure (nanostructure) on the corrosion properties of metals remains unclear. This is in large part a result of the presence and nature of structural and chemical defects, which result typically in regions of structural and chemical inhomogeneity. These sites often dominate corrosion behavior.[1–3] The lack of long-range order, grain boundaries, and defects in amorphous alloy systems is thought to be a key beneficial characteristic leading to the concept that amorphous alloys possess superior corrosion resistance compared with their crystalline counterparts.[4] However, it is becoming increasingly clear that corrosion resistance of amorphous alloys benefits from (1) accommodating a large concentration of passivating or dissolution-inhibiting elements in solid solution,[5] (2) a lack of defects causing chemical or structural nonuniformities,[6] and (3) complex roles of minor alloying elements often added for other reasons.[7] In contrast, the role of nanostructured atomic arrangements on the corrosion behavior of amorphous and crystalline alloys has been elusive and is not well understood.[8–14] The transformation of disordered amorphous alloys to ordered single-phase crystalline alloys provides an ideal forum to study the role of structural ordering on the corrosion behavior without the accompanying complication of long-range chemical partitioning. However, D.J. HORTON, Graduate Research Assistant, and J.R. SCULLY, Charles Henderson Chaired Professor of Materials Science and Engineering Co-director, are with the Center for Electrochemical Science and Engineering, Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22904. Contact e-mail: [email protected] Manuscript submitted March 29, 2011. Article published online February 7, 2012 2706—VOLUME 43A, AUGUST 2012

previous studies led to inconsistent and sometimes contradictory conclusions regarding the effects of ordering without compositional change on the corrosion behavior of amorphous alloys. An increase,[8,9,11] decrease,[10,14] and minimal effect[12,13] from ordering have all been reported. This study focuses on corrosion of an amorphous solidsolution alloy compared with a stoichiometrically equivalent crystalline structure lacking other micrometer-scale defects. The preferential dissolution of one element from the matrix provides an ideal opportunity to use electrochemical techniques to explore the effect of ordering on this process. The role of ordering on preferential dissolution has been studied in the Cu3Au system, which undergoes a transformation from a disordered crystalline solid solution (face-centered cubic [fcc]) to an ordered crystalline state (L12). The ordered, single-phase exhibits passivity at higher potentials and has a higher critical dealloying potential than disordered crystalline Cu3Au.[15] The crystallographic orientation of the initial dealloying of (111) Cu3Au in sulfuric acid solution was studied carefully and low overpotential dealloying led to the formation of straine

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