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K.B. Kim Department of Advanced Materials Engineering, Sejong University, Gwangjin-gu, Seoul 143-747, Korea

J. Das IFW Dresden, Institute for Complex Materials, D-01069 Dresden, Germany

S. Yia) Department of Materials Science and Metallurgy, Kyungpook National University, Buk-gu, Daegu 702-701, Korea

J. Eckertb) IFW Dresden, Institute for Complex Materials, D-01069 Dresden, Germany (Received 5 January 2007; accepted 4 April 2007)

The effect of additional elements on microstructure and mechanical properties of (TiCu)-based bulk metallic glasses (BMGs) has been systematically investigated. Based on the values of the heat of mixing between the additional elements and the major constituent elements Ti and Cu, small additions of elements having a positive heat of mixing with Cu and a negative heat of mixing with Ti are effective in forming nanoscale heterogeneities upon solidification and enhance the ductility. It is experimentally demonstrated that the selection of the minor elements in (TiCu)-based BMGs plays a crucial role to induce nanoscale heterogeneities and thus to control the deformation behavior of the bulk metallic glasses.

I. INTRODUCTION

As materials for the next generation of structural and functional materials, monolithic bulk metallic glasses (BMGs) have been intensively developed during recent years due to their high strength, elastic strain limit, and corrosion resistance.1,2 However, monolithic BMGs usually undergo inhomogeneous plastic deformation at room temperature, which results in very limited overall plastic strain.3,4 To overcome this disadvantage of monolithic BMGs, several attempts have been made to improve the macroscopic ductility by introducing microscale ductile crystalline phases, effective in preventing the localization of the shear stress.5–7

a)

Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal 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.2007.0277 J. Mater. Res., Vol. 22, No. 8, Aug 2007

http://journals.cambridge.org

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Recently, a new class of BMGs with significant macroscopic ductility under compression, so-called “ductile BMGs,” have been developed in a series of Zr-,8 Pt-,9 Cu-,10,11 Pd-,12 and (ZrCu)-13,14 based alloys. For example, a simple binary Zr50Cu50 BMG with nanocrystals embedded in the amorphous matrix exhibits a high plastic strain of ∼50%.14 Furthermore, a Zr47.5Cu47.5Al5 BMG developed by addition of Al to improve the glassforming ability (GFA) of a binary Zr50Cu50 BMG15 shows high ductility as well as “work-hardening-like” behavior.13 Detailed microstructural investigations of the work-hardenable ductile Zr47.5Cu47.5Al5 BMG revealed unique heterogeneities consisting of nanoscale chemical fluctuations.16 Moreover, some areas of the sample contain a macroscopically different degree of the chemical16 and structural17 heterogeneities. Along the