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Haifeng Zhang and Aiming Wang Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China (Received 17 July 2011; accepted 5 December 2011)

The Zr65Al7.5Ni10Cu17.5 bulk metallic glasses were prepared by injection casting (casting temperature of 1100 °C) and in situ suction casting (casting temperature as high as 3000 °C). The strain-rate-dependent mechanical behaviors of the specimens were investigated under axial compression at room temperature over a wide strain rate range (1.6
105–1.6
101 s1). The specimens prepared by injection casting exhibited negative strain rate sensitivity, i.e., the yield stress decreased with increasing strain rate. In contrast, no strain rate sensitivity was observed for the specimens prepared by in situ suction casting. The different strain rate sensitivities in the specimens prepared at different temperatures were probably caused by the diversities of the local atomic structures.

I. INTRODUCTION

The bulk metallic glasses (BMGs), as a relatively young class of materials, exhibit unique mechanical properties by comparison with their crystalline counterparts.1 However, the poor ductility and subsequent premature fracture still limit their applications due to highly localized inhomogeneous deformation.2,3 Although many investigations on the inhomogeneous deformation of BMGs have been performed, the underlying deformation physics of BMGs remain less firmly established compared with crystalline alloys. Currently, there are still different explanations for the strain-rate-dependent mechanical behaviors for BMGs, even those explanations are in debate, which may be the key to obtaining insight into the physical processes responsible for the strength and ductility of BMGs. The effect of strain rate on the strength of BMGs has not been well established. Bruck et al.4 and Subhash et al.5 found that the compressive strength of Zr41.2Ti13.8Cu12.5Ni10Be22.5 BMG was independent of strain rate. However, negative strain rate sensitivity was found in Zr/Hf-based BMGs by Li et al.,6 Zr57Ti5Cu20Ni8Al10 BMG by Hufnagel et al.,7 Zr52.5Ti5Cu17.9Ni14.6Al10 BMG by Dalla Torre et al.,8 and Zr38Ti17Cu10.5Co12Be22.5 by Xue et al.9 On the contrary, Liu et al.,10 Zhang et al.,11 and Ma et al.12 reported that Nd60Fe20Co10Al10, Ti45Zr16Ni9Cu10Be20, and Ti40Zr25Ni8Cu9Be18 BMGs showed positive strain a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.430 J. Mater. Res., Vol. 27, No. 4, Feb 28, 2012

rate dependence on fracture stress, respectively. Mukai et al.13 reported that the Pd40Ni40P20 BMG exhibited no fracture stress varied during the strain rates increased from 103 to 2.8
103 s1 under tension, while the fracture stress decreased with increasing strain rate in the range from 3.3
103 to 1.7
103 s1 under compression.14 Dalla Torre et al.15 also reported that both Zr57.9Cu22Fe8Al12Pd0.1 and Cu50Zr50 BMGs exhibited a change in the strain rate sensitivity from negative to positiv