Fracture behavior of Zr 55 Cu 30 Al 10 Ni 5 bulk metallic glass under quasi-static and dynamic compression
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Fracture behavior of Zr55Cu30Al10Ni5 bulk metallic glass was investigated under quasi-static compression at strain rate of 10−4/s using an Instron testing machine and dynamic split Hopkinson bar (SHPB) compression with strain rate of about 1900–4300/s. Pronounced strain softening, especially past the peak stress, was observed under SHPB tests and compared with the distinct flow serrations under quasi-static tests. Scanning electron microscope revealed that the angle between the loading axis and major shear plane is less than 45°, deviating from the maximum shear stress plane. Microscopically, unlike the ordinary veinlike pattern found in quasi-static compression, the elongated veinlike pattern was observed at the onset position of rapid shearing under dynamic test. A closely arrayed dendritelike structure dominated the dynamic fracture, consequently, and should be the major pattern representing the rapid shear band propagation. In addition, a transition state from veinlike to dendritelike pattern was observed at the final instantaneous fracture region in quasi-static tests. Evidence revealed the characteristic dimension of dynamic fracture surface complies with Taylor’s meniscus instability criterion. The roles of free volume and adiabatic heating on the fracture strength and stress concentration on the fracture morphology are also discussed.
I. INTRODUCTION
Since the early 1990s, new Zr-based multicomponent glass-forming alloys, such as Zr–Cu–Al–Ni1 and Zr–Ti– Cu–Ni–Be,2 with very high glass-forming ability (GFA) have been discovered. Because of their low critical cooling rate, sizable bulk metallic glasses (BMGs) have been fabricated with conventional casting methods. Zr-based BMGs exhibit superior engineering properties such as high fracture strength under ambient static pressure, high hardness, soft magnetism, and good corrosion resistance.3,4 This class of BMGs can potentially be used in many commercial and industrial applications and even be used as kinetic penetrator. However, during industrial use, many components may experience dynamic loading. It is particularly essential to quantify BMGs’ dynamic constitutive behavior. Although the quasi-static mechanical properties and structural performance, as well as the deformation and fracture mechanisms of metallic glasses have been extensively studied,5–15 there have been limited investigations on the dynamic properties of monolithic BMGs.
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0217 1744 J. Mater. Res., Vol. 23, No. 6, Jun 2008 http://journals.cambridge.org Downloaded: 14 Mar 2015
They indicate that BMGs have remarkably high fracture toughness comparable to that of structural steels14–17 if a relatively low value of /B (ratio of the BMG’s intrinsic elastic shear modulus to the bulk modulus B) is satisfied.17 Localized shear bands usually dominate when they deform at room temperature (RT) under quasistatic,10–12 Hopkinton pressure bar,18–26 and shock wave27,28 compression tests. Limited investigations h
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