Plasticity of bulk metallic glasses improved by controlling the solidification condition
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P.K. Liaw Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996-2200
Y.D. Wang School of Materials and Metallurgy, Northeastern University, Shenyang 110004, China
Y. Ren Experimental Facilities Division, Advanced Phonon Source, Argonne National Laboratory, Argonne, Illinois 60439 (Received 15 October 2007; accepted 27 November 2007)
Different bulk metallic glasses (BMGs) were prepared in ductile Cu47.5Zr47.5Al5, Zr62Cu15.4Ni12.6Al10, and brittle Zr55Ni5Al10Cu30 alloys by controlling solidification conditions. The achieved microstructures were characterized by x-ray diffraction, differential scanning calorimetry, transmission electron microscopy, and synchrotronbased high-energy x-ray diffraction. Monolithic BMGs obtained by high-temperature injection casting are brittle, while BMGs bearing some nanocrystals with the size of 3 to 7 nm and 2 to 4 nm, obtained by low-temperature injection casting and in situ suction casting, respectively, exhibit good plasticity. It indicates that the microstructures of BMGs are closely affected by the solidification conditions. Controlling the solidification conditions could improve the plasticity of BMGs.
I. INTRODUCTION
Bulk metallic glasses (BMGs) have already been prepared in many alloy systems, such as Zr-, Fe-, Mg-, Cu-, and Ti-based alloys.1–5 Most BMGs reported exhibit little macroscopic plasticity (almost none in tension and below 1% under compression) at room temperature.1,3 However, distinct macroscopic plasticity in some monolithic BMGs has been reported recently.6–8 This trend has raised the hope that brittleness might not be the intrinsic property of monolithic BMGs at room temperature. Some researchers believed that the good plasticity is contributed by the local ordering structures9–13 embedded in the glassy matrix, which could not be easily identified by common techniques, i.e., x-ray diffraction (XRD). Accordingly, how to obtain such a microstructure is important to improve the plasticity of BMGs. In this paper, we prepare BMGs in alloy systems commonly regarded as ductile and brittle materials. Solidification conditions were controlled to achieve different microstructures. The relationa)
Address all correspondence to this author. e-mail:[email protected] DOI: 10.1557/JMR.2008.0127 J. Mater. Res., Vol. 23, No. 4, Apr 2008
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ship between the microstructure and mechanical property conclusively indicated that the plasticity of BMGs can be improved by controlling the solidification condition. We believe that the microstructure of BMGs plays a significant role in affecting their mechanical performance. The BMG microstructure is largely influenced by the alloy composition and preparation method. Both ductile and brittle BMG alloys were selected in this study: Cu47.5Zr47.5Al5,14 Zr62Cu15.4Ni12.6Al10,9 and Zr55Ni5Al10Cu30.15 The former two are commonly regarded as ductile BMGs,9,14 while the latter is brittle.15 During the rapid solidification, it is well known that B
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