The Effect of Purification on the Glass-Forming Ability of a Pd-Cu-Si Alloy
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METALLIC glass was first developed by Klement et al.[1] in 1960. Now it is known that a sample that possesses full amorphous structure and reaches 1 mm in each dimension is arbitrarily defined as bulk metallic glass (BMG). Since bulk metallic glassy alloys exhibit many excellent properties and potential applications, and can serve as model materials for studying the fundamental problems related to amorphous structure, they have received tremendous passion from researchers in many fields.[2–4] The first bulk form amorphous alloy material was discovered in the Pd-Cu-Si, Pd-Ag-Si, and Pd-Au-Si alloys by Chen and Turnbull[5] in 1969, but they did not point out the sample’s shape and size. In 1976, Chen and Coleman[6] reported research results with /0.5-mm Pd-Cu-Si rod prepared by water quenching using a sealed quartz tube. Later, in 1981, Steinberg et al.[7] prepared a bulk amorphous sphere in Pd77.5Cu6Si16.5 by free-fall containerless solidification and clearly pointed out the prepared glassy ball with a diameter of about 1.5 mm. Since then, no large size Pd-Cu-Si BMG was reported until very recently.[8,9] As a kind of metastable material, the formation of BMG is strongly affected by the fabrication technique. In order to improve the glass forming ability (GFA) and increase the critical size of BMGs, two major routes were H.Y. DING, Y. LI, and G.N. YANG, Postdoctoral Candidates, and K.F. YAO, Professor, are with The Key Laboratory for Advanced Materials Processing Technology, Department of Mechanical Engineering, Tsinghua University, Beijing 100084, P.R. China. Contact e-mail: [email protected] S.B. QIU, Postdoctor, formerly with The Key Laboratory for Advanced Materials Processing Technology, Department of Mechanical Engineering, Tsinghua University, is now with the Institute of Industry Technology, Guangzhou and Chinese Academy of Science, Guangzhou 511458, P.R. China. Manuscript submitted March 31, 2011. Article published online July 29, 2011 2610—VOLUME 43A, AUGUST 2012
applied. One method is to increase the cooling rate to avoid crystallization, and the other is to stabilize the melt and suppress the heterogeneous nucleation during the cooling process so that the amorphous structure could be obtained at room temperature. Among these methods, the melt purification by B2O3 fluxing was found to be helpful in enhancing the GFA of BMGs, especially in some Pd- and Fe-based alloys. In 1984, Kui et al.[10] prepared a Pd-Ni-P glassy ball with a diameter of 10 mm by fluxing and water quenching, and this was the first BMG that reached a critical size of 10 mm (1 cm). Later in 1996, He et al.[11] increased the critical size up to 25 mm, showing a great potential of melt purification on improving GFA of the Pd-Ni-P alloy. Other important progress in preparing BMGs is the discovery that copper mold casting can be employed to prepare BMG samples.[12] As a result, many new bulk glassy alloys were developed by this method. Especially, most reported BMGs are now prepared by copper mold casting. As we know, the structure and prop
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