Alloying effects of iridium on glass formation and glass-forming ability of the Zr-Cu-Al system
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ei Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6115
Z.P. Lua) State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China (Received 12 November 2008; accepted 5 February 2009)
Alloying effects of iridium on the glass formability (GFA) of the Zr–Ir–Cu–Al system have been investigated, and several new bulk metallic glasses (BMGs) with high GFA have been successfully developed. Additions of Ir in the Zr–Cu–Al system can yield a beneficial distribution in atomic sizes, but the strong chemical interaction of the Zr–Ir atomic pair limits the maximum addable Ir contents and the resultant GFA. Our analyses indicate that the optimum composition for alloying elements is determined by not only topological but also chemical factors. Phase competition upon solidification, rather than effects from individual affecting factors, dictates the GFA of BMG systems.
In the design of bulk metallic glasses (BMGs), it is imperative to know what kind of systems can be selected for glass formation and how to quickly locate the glassforming compositions with large glass-forming ability (GFA) in such systems. A great deal of serious scientific effort has been devoted to this area, and many assistive scenarios for developing novel BMGs, such as the famous three empirical rules, have been proposed.1–5 It is well accepted that deep eutectic systems favor glass formation, and good glass formers in these systems are preferentially located at/near the eutectic.6–12 However, for a system containing multiple constituent elements that are necessary for enabling large GFA, it is hard to know if the system has deep eutectics and where the good glass-forming compositions are located. As a result, attention has been directed to establishing practical methods for exploring good glass formers in the multiple component systems. As an example, we have recently proposed a concept of so-called “ideal” glass-forming liquids in which binary eutectics from strong atomic pairs can be treated as basic composition units for designing BMGs.13,14 Starting compositions for exploring new BMGs in these unique systems can be obtained simply by properly mixing the binary eutectics. Compared with the use of the individual element concentration, this a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0188 J. Mater. Res., Vol. 24, No. 5, May 2009
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approach not only dramatically reduces the total number of alloys needed to be investigated, but also can quickly locate novel BMGs with high GFA.13,14 In this paper, we will apply this approach to the Zr–Cu–Ir–Al system to investigate effects of iridium on glass formation and GFA as a main constituent. To select proper alloying elements for glass formation, Inoue1 and others15,16 first proposed that additional elements having large atomic mismatches with the major constituent and high tenden
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