Liquid Structures of Metallic Glass-forming Binary Zr Alloys
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1152-TT03-06
Liquid Structures of Metallic Glass-forming Binary Zr Alloys Akitoshi Mizuno1, Toshihiko Akimoto 1, Masahito Watanabe1, Shinji Kohara2 and Masaki Takata2,3 1 Department of Physics, Gakushuin University, Mejiro, Tokyo 171-8588, Japan 2 Japan Synchrotron Radiation Research Institute /SPring-8, Sayo-gun, Hyogo 679-5198, Japan 3 SPring-8/RIKEN, Sayo-gun, Hyogo 679-5148, Japan ABSTRACT We have analyzed liquid structures of the binary Zr-TM (TM=Pd, Cu, Ni) alloys as a function of composition to investigate relations with their glass-forming abilities. High-energy xray (E=113 keV) diffraction experiments were performed and a conical nozzle levitation (CNL) technique was applied to achieve a containerless condition for highly reactive melts with high temperature. Structure information of the liquid alloys has been obtained with the aid of reverse Monte Carlo simulation. A shoulder was found at high-Q side of the second peak for the structure factor for Zr70Pd30 as well as Zr70Cu30 alloy Zr50Cu50 alloys, which can be indication of the formation of ISRO in the liquid alloys. Liquid Zr-Ni alloys shows an apparent difference in the structure factors between the Zr70Ni30 and the Zr50Ni50 alloys, which can be associated with the formation of the chemical short range ordering, whereas the Zr-Pd alloys show a typical random distribution of atoms. INTRODUCTION Since the findings of the bulk metallic glass-forming alloys, it has been empirically confirmed that multicomponent alloys with three or more elements should be prepared to yield bulk metallic glasses (BMGs)[1]. However, recent experimental studies have shown that BMGs can be formed even from the binary alloys such as Zr-Cu, Ni-Nb and Cu-Hf systems [2,3]. Despite a lot of effort has been devoted to studies on BMGs, the origin of the high thermal stability of the undercooled liquid state has not been fully clarified in particular from a microscopic point of view. As originally pointed out by Frank [4], the formation of local icosahedral short-range ordering (ISRO) in undercooled liquids can be an activation barrier to crystallization due to the fivefold rotational symmetry of the icosahedron, which is incompatible with long-range periodicity. In fact, recent diffraction experiments using synchrotron x-rays or neutrons have indicated the formation of local ISRO in the undercooled liquid state not only for multicomponent Ti-Zr-Ni alloys [5], but also for supercooled elemental liquids, such as Zr, Ni and Fe [6]. As for metallic glass-forming alloys, the local ISRO was detected in liquid ZrxCu(100x) alloys (x = 50 and 70) even above their melting temperature [7,8]. Furthermore, it was reported that binary Zr70TM30 (TM=Pd, Cu, Ni) metallic glasses form the Zr atom-centered icosahedra [911] as well as multicomponent Zr-Ti-Al-Cu-Ni metallic glasses [12]. These results suggest that the formation of local ISRO in metallic liquids is a dominant factor in stabilizing the metastable phase including the undercooled liquid state. Besides, the glass forming ability resulted from
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