Structural origin of the high glass-forming ability in Y-doped bulk metallic glasses
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Guo-Qing Zhang Key Laboratory of Advanced Textile Materials and Manufacturing Technology (Zhejiang Sci-Tech University), Ministry of Education, Hangzhou 310018, People’s Republic of China
Lian-Yi Chenb) International Center for New-Structured Materials (ICNSM), Zhejiang University, Hangzhou 310027, People’s Republic China; and Laboratory of New-Structured Materials, Department of Materials Science and Engineering; Department of Physics, Zhejiang University, Hangzhou 310027, People’s Republic of China (Received 25 February 2010; accepted 18 May 2010)
Structural origin of the high glass-forming ability (GFA) in multicomponent bulk metallic glasses (BMGs) caused by minor alloying was investigated using state-of-the-art synchrotron radiation techniques. It is found that a two-shell icosahedral cluster with one Y center is the basic structural unit in the representative Cu46Zr42Al7Y5 BMG, which may be densely packed with the help of shared and glue atoms, leading to enhanced ordering at short and medium range. This cluster dense packing may play a key role in achieving the high GFA in CuZrAlY alloy, which also explains the strong dependence of GFA on Y content observed in many experiments. The present work may be extended to a series of multicomponent amorphous alloys, the formation of which is strongly dependent on minor alloying.
I. INTRODUCTION
Recently, extensive efforts have been made to search for novel bulk metallic glasses (BMGs) with high glassforming ability (GFA) and unique properties, which may have potential application as engineering materials.1,2 It is found that BMGs based on late-transition metals (e.g., Cu, Fe, Ni, and Co) may be such promising materials because they usually have excellent mechanical properties and are much less expensive than those based on noble metals.3–5 However, many of these types of binary or ternary alloys can only be fabricated into amorphous rods with critical diameter less than 5 mm.6–8 Fortunately and interestingly, several BMGs were prepared recently by adding a minor amount of the fourth element into ternary copper-based alloys. The critical casting sizes of these alloys were greatly enhanced from millimeter to centimeter scale, such as those found in Cu–Zr–Al–Ag,9,10 Cu–Zr–Ag–Ti,11 Cu–Zr–Al–Gd,12,13 and Cu–Zr–Al–Y14 systems. In particular, a group of ZrCu(Hf)AlY BMGs with critical diameter of 12 to 18 mm were fabricated by “3D pinpointing Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2010.0236 J. Mater. Res., Vol. 25, No. 9, Sep 2010
approach.”15 The GFA increase in these BMGs usually strongly depends on the concentration of the added elements. Normally, the GFA was attributed to moving to the eutectic compositions or the effect of oxygen.14,16–18 GFA may also strongly relate to atomic structure of BMGs.19–21 However, structural study of these BMGs is still inadequate.19 In this work, we try to unravel the origin of the high GFA induced by minor alloying from structural aspect by investigati
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