Microstructure and mechanical properties of slowly cooled Cu 47.5 Zr 47.5 Al 5
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. Pauly and C. Duhamel FG Physikalische Metallkunde, FB 11 Material- und Geowissenschaften, Technische Universität Darmstadt, D-64287 Darmstadt, Germany
B.C. Wei Institute of Mechanics, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China
J. Eckertb) FG Physikalische Metallkunde, FB 11 Material- und Geowissenschaften, Technische Universität Darmstadt, D-64287 Darmstadt, Germany; and Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden, D-01069 Dresden, Germany (Received 15 June 2006; accepted 3 August 2006)
Cu47.5Zr47.5Al5 was prepared by arc melting and solidified in situ by suction casting into 2–5-mm-diameter rods under various cooling rates (200–2000 K/s). The microstructure was investigated along the length of the rods by electron microscopy, differential scanning calorimetry and mechanical properties were investigated under compression. The microstructure of differently prepared specimens consists of macroscopic spherical shape chemically inhomogeneous regions together with a low volume fraction of randomly distributed CuZr B2 phase embedded in a 2–7 nm size clustered “glassy-martensite” matrix. The as-cast specimens show high yield strength (1721 MPa), pronounced work-hardening behavior up to 2116 MPa and large fracture strain up to 12.1–15.1%. The fracture strain decreases with increasing casting diameter. The presence of chemical inhomogenities and nanoscale “glassy-martensite” features are beneficial for improving the inherent ductility of the metallic glass.
I. INTRODUCTION
Since Zr-based bulk metallic glasses (BMGs) with high glass-forming ability were fabricated,1 many interesting mechanical and physical properties of BMGs have been investigated2–5 for commercial applications. The major advantages of BMGs are high strength, low elastic modulus, and good wear properties.2,6 However, the final fracture of BMGs occurs catastrophically and involves very little overall plastic deformation due to highly localized shear banding.6 To overcome the problem of limited plasticity in BMGs, several composite materials have been developed,7–17 which can be broadly classified a)
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http:// www.mrs.org/jmr_policy. DOI: 10.1557/JMR.2007.0033 326 J. Mater. Res., Vol. 22, No. 2, Feb 2007 http://journals.cambridge.org Downloaded: 15 Mar 2015
in two groups according to their processing: (i) ex situ and (ii) in situ formed composites. Several trials have previously been made to improve the ductility by introducing quasicrystalline18,19 or nanocrystalline20,21 precipitates in a glassy matrix upon partial crystallization during annealing treatment of the amorphous precursors. The ex situ composites are formed by directly introducing a crystalline solid phase as reinforcement into the glass-forming melt during processing and consist of either pa
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