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P. Feng State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, China

Y. Zhanga) State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China

Q.M. Zhang State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, China

P.K. Liaw Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996-2200

G.L. Chen State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China (Received 17 October 2009; accepted 21 January 2010)

Quasi-static and dynamic deformation behaviors of Zr-based bulk-metallic-glass-matrix composites, fabricated by Bridgman solidification, were investigated in this study. Upon quasi-static compressive loading, the composites exhibit ultrahigh strength, accompanied by considerable plasticity. The multiplication of shear bands on the lateral surface of deformed samples, and the highly-dense liquid drops on the fracture surface, are in agreement with the improved plasticity. However, upon dynamic loading, the mechanical properties of the composites deteriorate considerably, due to insufficient time to form profuse shear bands. The strain-rate responses of the mechanical properties of the crystalline alloys and the in situ and ex situ bulk metallic glass composites are compared, and the different deformation mechanisms of the in situ composites upon quasi-static and dynamic loading are explained.

I. INTRODUCTION

Since the first metallic alloy was vitrified by rapidly cooling the melts,1 amorphous alloys have been developed to the point where centimeter-scale billets can be cast.2 These bulk metallic glasses (BMGs) exhibit high yield strength, high fracture strength, large elastic strain, and superior corrosion and wear resistance.2 This collection of properties renders them potential candidates for usage as engineering materials. However, most BMGs exhibit little compressive plasticity and no tensile ductility at room temperature, due to shear localization upon loading. The rapid propagation of individual shear bands dominates the failure. In order to improve the plasticity a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0289

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http://journals.cambridge.org

J. Mater. Res., Vol. 25, No. 12, Dec 2010 Downloaded: 13 Mar 2015

of BMGs, a series of in situ BMG-matrix composites have recently been developed.3–6 The crystalline phases with the dendritic morphology are precipitated within the glass matrix during the cooling, and can retard and deflect the prompt propagation of critical shear bands upon loading. Consequently, compressive plasticity is greatly improved. Johnson et al.3–5 successfully used copper-mold suction casting and semi-solid processing to control the volume fraction of crystalline phases for in situ BMG-matrix composites. We have controlled the volume fraction of crystall