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Zr-based bulk metallic glasses are promising engineering materials due to their good glass-forming abilities and unique combination of good strength (;1.9 GPa) and medium stiffness. In this study, the corrosion behaviors of Zr–Co–Al–Ag BMGs, with silver content from 0 to 11 at.%, in NaCl and H2SO4 solutions were investigated. The corrosion resistance increased when the silver content increased. The oxidation behaviors of Zr–Co–Al–Ag BMGs were also studied. The oxidation kinetics of all the samples obeyed a two-stage parabolic rate law, which consisted of an initial transient oxidation followed by a steady-state oxidation stage. The addition of Ag was found to reduce the oxidation resistance of Zr–Co–Al–Ag BMGs. Some white nodules, possibly cobalt oxide, were observed when the Zr–Co–Al–Ag BMG with 8 at.% Ag was oxidized at high temperature.

I. INTRODUCTION

Zr-based BMGs have attracted much attention in the past decades due to their high glass-forming abilities and unique combination of superior strength (;1.9 GPa), Young’s modulus up to 100 GPa, and high elastic strain limit of around 2%.1 The corrosion resistance of the alloys is also very good, and is better than a lot of other crystalline alloys or stainless steels.2 These properties together with good formability in the supercooled liquid region make the bulk metallic glasses a promising engineering material for some niche applications like ball bearings for shot-peening and micromotors.3–6 Zr–Co–Al BMGs are a recently developed BMG system with good mechanical properties and corrosion resistance.7–10 The critical diameter for glass-forming of Zr–Co–Al BMGs is up to 18 mm.11,12 Recently, silver was introduced to this system for enhancing the glass-forming ability and the critical diameter increased up to 20 mm.13 In addition to the above considerations, the corrosion and oxidation resistance are also important factors for industrial application. BMGs are structurally homogeneous and have no grain boundaries and defects like dislocations. They in general do not suffer from nonuniform corrosion. However, impurities inevitably exist in practice and will upset the uniform structure of BMGs. In addition, the surface atoms of BMGs are more active and have higher energy compared to the surface atoms of crystalline alloys.2,14 Amorphous alloys therefore sometimes exhibit lower corrosion resistance compared to their crystalline counterparts.

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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.107 1248

J. Mater. Res., Vol. 29, No. 11, Jun 14, 2014

http://journals.cambridge.org

Downloaded: 10 Jul 2014

The study of the corrosion behaviors of BMGs is useful for designing methods to improve the corrosion resistance of BMGs, such as spraying,15,16 controlled oxidation,17,18 ion implantation,19,20 and laser processing.21,22 It is important to determine the resistance of the Ag-bearing Zr–Co–Al BMGs to harsh environment when assessing its viability for various applications. In this paper, the corrosion and oxidation behav