Temperature increases caused by shear banding in as-cast and relaxed Zr-based bulk metallic glasses under compression
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H. Choo Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996-2200; and Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
P.K. Liaw Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996-2200
B.J. Edwards and B. Khomami Department of Chemical and Biomolecular Engineering, The University of Tennessee, Knoxville, Tennessee 37996-2200 (Received 21 March 2008; accepted 24 July 2008)
Using an infrared camera, the temperature evolution of as-cast and relaxed bulk metallic glasses during compression was measured. Substantial variations in the temperatures of both glasses during plastic deformation were observed, which are conjectured to result at least partially from shear-banding phenomena. The relaxed glass has a larger temperature rise than the as-cast glass, which can be attributed to a reduction in the free volume. The larger temperature increase in the relaxed glass may be responsible for the observed work softening. The relaxed glass also has a higher maximum temperature than the as-cast, which can be attributed to a stronger strain-rate dependence of the temperature rise rate, and a shorter dissipation time scale for the heat due to conduction. The experimental data follow the well-known model behavior, and suggest the possibility of a statistical correlation between the fluctuations of strain rates and the rates of the temperature variation.
I. INTRODUCTION
Metallic glasses have received extensive interest due to their extraordinary physical, chemical, and mechanical properties.1–7 The recent development of bulk metallic glasses (BMGs) allows the use of metallic glasses as structural materials.1,2 However, the poor ductility and subsequent catastrophic fracture of these new materials severely limit their structural applications. At low homologous temperatures, the plastic deformation of BMGs is restricted to highly localized shear bands.8,9 The excessive propagation of individual shear bands may cause premature fractures. Temperature increases during shear banding in metallic glasses have been proposed for over three decades.10–13
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0355 J. Mater. Res., Vol. 23, No. 11, Nov 2008
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It was assumed that the temperature increases may play a critical role in shear-banding phenomena, subsequent deformation, and fracture. Recent experimental research using an infrared (IR) camera/detector14–17 and a fusible coating approach18 verified the significant increases in the temperature in shear bands. However, there is still a large discrepancy in estimating temperature increases from one-hundredth to several thousand degrees,10–18 which may be related to the strong dependence of shear banding on intrinsic glassy structures and external loading conditions. Metallic glasses have a varying amount of free volume, which is entrapped
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