Deformation and failure of Zr 57 Ti 5 Cu 20 Ni 8 Al 10 bulk metallic glass under quasi-static and dynamic compression
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T. Jiao and Y. Li Department of Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland 21218
L-Q. Xing Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218
K.T. Ramesh Department of Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (Received 24 October 2001; accepted 20 March 2002)
We have examined the mechanical behavior of Zr57Ti5Cu20Ni8Al10 bulk metallic glass under uniaxial compression at strain rates from 10ā4 to 3 Ć 103 sā1. The failure stress decreases with increasing strain rate, and shear-band formation remains the dominant deformation mechanism. A consideration of basic properties of adiabatic shear bands makes it appear unlikely that shear bands formed under quasi-static loading are adiabatic; in the dynamic case, the time scales of deformation and thermal conduction are similar, indicating that a more sophisticated calculation is required. In the dynamic tests, however, high-speed cinematography reveals evidence that the mechanism of failure involves an adiabatic component.
I. INTRODUCTION
II. EXPERIMENTAL PROCEDURE
Bulk amorphous alloys and composites have a unique combination of properties that makes them potentially attractive structural materials. For instance, they can combine high strength with high toughness and can be easily processed in the supercooled liquid state.1 Most recent studies of the mechanical behavior of bulk metallic glasses have focused on Zr41.25Ti13.75Cu12.5Ni10Be22.5. These studies include examination of mechanical behavior under quasi-static and dynamic loading2,3 and fracture toughness. 4ā6 The dynamic properties are of particular interest, because bulk amorphous alloys are potential replacements for depleted uranium in armorpiercing projectiles. In this paper, we report on the deformation and fracture characteristics of a bulk amorphous alloy, Zr57Ti5Cu20Ni8Al10, that does not contain beryllium. We observe that the failure stress decreases monotonically with increasing strain rate. The dominant deformation mechanism (shear-band formation and propagation) is the same at all the strain rates that we examined. These observations are in contrast to the dynamic behavior of most crystalline metals, in which the flow stress increases with increasing strain rate (typical crystalline metals deform plastically, without macroscopic failure, during dynamic compression).
We prepared the samples used in this study by arc melting master alloy ingots of the desired composition from high-purity elemental starting materials under a Tigettered Ar atmosphere. To produce the metallic glass, we remelted the master alloy ingots and cast the molten alloy into a copper mold to produce 3-mm-diameter rods. Right circular cylinders of 3-mm diameter and 6-mm long (for the quasi-static compression tests) or 1.8-mm long (for the dynamic compression tests) were machined from the cylindrical rods by electrical discharge machining. The ends of the samples were lapped to ensure parallelism to each other and orthogo
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