Enhanced Plasticity of Zr-based Bulk Metallic Glass Matrix Composite with Ductile Reinforcement
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C. Wei, Y.R. Wang, and W.H. Li National Microgravity Lab, Institute of Mechanics, Chinese Academy of Sciences, Beijing 10080, People’s Republic of China
C.H. Sheka) Department of Physics and Materials Science, City University of Hong Kong, Hong Kong (Received 27 January 2005; accepted 26 April 2005)
A composite material containing uniformly distributed micrometer-sized Nb particles in a Zr-based amorphous matrix was prepared by suction cast. The resulting material exhibits high fractured strength over 1550 MPa and enhanced plastic strain of about 29.7% before failure in uniaxial compression test at room temperature. Studies of the serrations on the stress–strain curves and the shear bands on the fractured samples reveal that the amplitude of the stress drop of each serration step corresponds to the extent of the propagation of a single shear band through the materials. The composite exhibits more serration steps and smaller amplitude of stress drop due to the pinning of shear band propagation by ductile Nb particles.
I. INTRODUCTION
Recently, extensive investigations have been done in the development of bulk metallic glass (BMG) matrix composites. Attempts are made to improve the plasticity of the monolithic BMG, which typically display limited plastic strain of 0–2% in compression and nearly zero in tension at room temperature due to the highly localized shear bands.1–5 For example, some Zr-based BMG matrix composites containing micrometer-sized ductile crystalline phases such as body-centered-cubic (bcc) structured  dendrite or refractory metals, e.g., Nb, Ta, and W, exhibit combinations of the high strength of the amorphous matrix and the high ductility of the reinforcement. The achievements greatly expand the potential application of BMGs.6–10 The reinforcement in the composite material is known to resist the propagation of the highly localized shear bands effectively and promote the generation of multiple shear bands. Delayed failure and improved toughness of the materials result. However, the interaction of the reinforcement and the shear bands is still not very clear. Greer et al.11 and Chen et al.12 proposed that nanocrystalline particles with the scale
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0320 2386
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 9, Sep 2005 Downloaded: 14 Mar 2015
comparable with the thickness of the shear bands could influence the development of the shear bands. However, Hays et al.10 and Kühn et al.13 believed that particles with a mean size close to the width of the shear bands have little effect in stopping its propagation. In any case, the interaction between the shear bands and the second phase can be reflected by the shear bands characterization on the fractured plane and the serrated flow variation during the compression test or nanoindentation test. For example, Wei et al. proposed that a change from the serrated flow for monolithic BMGs to continuous flow for Nb-based BMG composites would occur.14 In
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