The oxidation behavior of Cu 42 Zr 42 Al 8 Ag 8 bulk metallic glasses
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The oxidation behavior of Cu42Zr42Al8Ag8 bulk metallic glasses W. H. Cao • J. L. Zhang • C. H. Shek
Received: 10 September 2011 / Accepted: 16 January 2012 / Published online: 19 September 2012 Ó The Author(s) 2012. This article is published with open access at Springerlink.com
Abstract The oxidation behavior of Cu42Zr42Al8Ag8 bulk metallic glass was studied in synthetic air over the temperature range of 330–460 °C. The oxidation kinetics of the metallic glass follows a single parabolic rate law at 330 and 390 °C and a two-stage parabolic rate law from 420 to 460 °C. Silver precipitates on the topmost oxide layer of the metallic glass were revealed by energydispersive X-ray spectroscopy together with X-ray diffraction pattern. Observation using scanning electron microscopy shows that silver metal precipitated at all temperatures and some islands were formed on the outermost copper oxide layer at high temperatures. Multilayered oxide scales were also observed with silver precipitates sandwiched between copper- and zirconium-rich oxides layers.
Introduction Bulk metallic glasses (BMGs) have received much interest in recent years because of their importance in both theoretical studies and industrial applications. Among those BMG systems developed, Cu–Zr-based BMGs are among the most popular amorphous alloys that possess the advantages of low material cost, superior mechanical properties, and good glass-forming ability (GFA) [1–5]. Recent works reported that a Cu–Zr-based Cu42Zr42Al8Ag8 alloy with large critical dimensions and high fracture strengths can be prepared by copper mold casting [6, 7]. The large GFA, superior mechanical properties, and Ni-free nature, endowed such metallic glasses with potential W. H. Cao (&) J. L. Zhang C. H. Shek Department of Physics and Materials Science, City University of Hong Kong, Kowloon Tong, Hong Kong, China e-mail: [email protected]
applications in not only structural materials but also biomaterials. However, the investigations of the environmental behavior of metallic glasses in such systems are very limited [8, 9]. It was reported that elemental metals such as nickel [10], copper [11–14], and noble metal (palladium, platinum, and gold) [14–16] could be separated or precipitated out during oxidation of zirconium-containing metallic glasses. However, few investigations have been conducted on the oxidation behavior of silver containing glassy alloy. Recently, Kai et al. [9] investigated the air oxidation of Cu45Zr45Al5Ag5 BMGs and found the precipitation of Ag elemental metal and they suggested that the precipitation played a partly blocking effect in the oxidation of Cu45Zr45Al5Ag5 BMGs. In our previous investigation on oxidation behavior of Cu42Zr42Al8Ag8 below glass-transition temperature [17], precipitation of mushroom-like elemental silver particles was observed. However, the precipitation accelerated the oxidation instead of retarding it as suggested in Cu45Zr45Al5Ag5 BMGs. In this article, the oxidation kinetics of Cu42Zr42 Al8Ag8 BMGs was investigated in detail
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