Corrosion Behavior of Fe 41 Co 7 Cr 15 Mo 14 C 15 B 6 Y 2 Bulk Metallic Glass in Sulfuric Acid Solutions
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TRODUCTION
AMORPHOUS alloys, in general, exhibit high corrosion resistance.[1–12] Particularly, the Fe-based amorphous alloys have the reputation of exhibiting superior corrosion resistance.[6–12] As early as 1974, people found that the melt-spun Fe-based amorphous alloys, Fe-CrP-C, had extremely high corrosion resistance in HCl solutions.[6] The excellent corrosion resistance of Fe-based amorphous alloys has been explained in terms of their structural and chemical homogeneity. Because amorphous alloys are structurally and chemically homogeneous, they lack microstructural features, such as grain boundaries and precipitates, which act as local electrochemically active sites.[5] Apart from the structural homogeneity, the chemical composition of Fe-based amorphous alloys has a great influence on corrosion resistance. Thus, the addition of appropriate elements in Fe-based amorphous alloys remarkably reduces the corrosion rate.[7–10] The addition of Mo, W, and Cr in amorphous Fe-P-C alloys increases the corrosion resistance significantly. For example, amorphous Fe-Cr, Fe-Mo and Fe-W alloys are resistant to pitting in 1 mol/l HCl solutions.[9] Li et al. found that amorphous Fe-Cr-Ni-Ta alloys were spontaneously passive in 12 mol/l HCl solutions, and the corrosion rates of the alloys containing Ta were six orders of H.B. FAN, Associate Professor, W. ZHENG, Ph.D. Student, and J. SHEN, Professor, are with the State Key Laboratory of Advanced Welding Production Technology, Harbin Institute of Technology, Harbin 150001, P.R. China. Contact e-mail: [email protected] G.Y. WANG, Senior Research Fellow, and P.K. LIAW, Professor, are with the Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996. Manuscript submitted April 10, 2010. Article published online October 19, 2010 1524—VOLUME 42A, JUNE 2011
magnitude lower than a type 304 stainless steel.[10] However, the glass-forming ability (GFA) of these Fe-based amorphous alloys is poor, and because they are mostly fabricated as thin ribbons or wires, the practical application of these amorphous alloys is limited. Since bulk Fe-based amorphous alloys first were reported in 1995,[13] a series of Fe-based amorphous alloys with a high GFA have been developed.[14–22] The amorphous alloy Fe41Co7Cr15Mo14C15B6Y2 exhibits an excellent GFA[20]; its critical diameter, which is the maximum casting diameter where the cooling rate is higher than the critical cooling rate to form an amorphous structure, can reach up to 16 mm. Although the mechanical properties of this amorphous steel have been reported,[23,24] little data exists on its corrosion behavior. If the amorphous steel Fe41Co7Cr15Mo14C15B6Y2 has excellent corrosion resistance in aggressive environments, then it could be an interesting candidate for technical and functional applications. The purpose of this article is to study the corrosionresistance behavior of the amorphous steel Fe41Co7Cr15Mo14C15B6Y2 in sulfuric-acid solutions and to compare it with the commercial stainless steel SUS 321, whos
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