Spall strength and Hugoniot elastic limit of a zirconium-based bulk metallic glass under planar shock compression
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John J. Lewandowskib) Case School of Engineering, Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106-7222 (Received 2 July 2006; accepted 4 October 2006)
Results are presented on the shock response of a zirconium-based bulk metallic glass (BMG), Zr41.25Ti13.75Ni10Cu12.5Be22.5, subjected to planar impact loading. An 82.5-mm bore single-stage gas-gun facility at Case Western Reserve University, Cleveland, OH, was used to conduct the shock experiments. The particle velocity profiles, measured at the back (free) surface of the target plate by using the velocity interferometer system for any reflector (VISAR), were analyzed to (i) better understand the structure of shock waves in BMG subjected to planar shock compression, (ii) estimate residual spall strength of the BMG after different levels of shock compression, and (iii) obtain the Hugoniot elastic limit (HEL) of the material. The spall strength was found to decrease moderately with increasing levels of the applied normal impact stress. The spall strength at a shock-induced stress of 4.4 GPa was 3.5 GPa while the spall strengths at shock-induced stresses of 5.1, 6.0, and 7.0 GPa were 2.72, 2.35, and 2.33 GPa, respectively. The HEL was estimated to be 6.15 GPa.
I. INTRODUCTION
Amorphous metals, also referred to as metallic glasses, differ from ordinary metals in that their constituent atoms are not arranged on a crystalline lattice. Because of their randomly ordered atomic structures, metallic glasses are known to exhibit unusual mechanical properties, such as near theoretical strength, large elastic strains, high hardness, excellent wear and corrosion resistance, and increased fracture toughness when compared to other brittle, high compressive strength materials.1,2 Nevertheless, until recently, amorphous metals have largely been manufactured in the form of thin ribbons, usually less than 1 mm thick because fast cooling rates (∼106 K/s) are required for retaining the metastable amorphous phase. The first reported bulk amorphous metals were Pd-based alloys designed in the early 1980s. The real breakthrough
a)
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this focus issue 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.2007.0053 402 J. Mater. Res., Vol. 22, No. 2, Feb 2007 http://journals.cambridge.org Downloaded: 13 Mar 2015
came during the period from 1988 to 1990, when Inoue discovered multicomponent liquid alloys with very deep eutectics that were capable of freezing to a glassy state several centimeters thick utilizing conventional cooling methods. 3 At around the same time, at Caltech, Johnson’s group developed Zr–Ti-based and other sizable amorphous metals. These zirconium-based bulk metallic glasses have been of particular interest to the engineering community because of their low critical cooling rate (1 K/s)
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