Structure of shear bands in Pd 40 Ni 40 P 20 bulk metallic glass
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Structure of shear bands in Pd40Ni40P20 bulk metallic glass Y.M. Chen Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-0047, Japan
T. Ohkubo and T. Mukai National Institute for Materials Science, Tsukuba 305-0047, Japan
K. Honoa) National Institute for Materials Science, Tsukuba 305-0047, Japan; and Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-0047, Japan (Received 20 February 2008; accepted 18 September 2008)
The atomic structure of shear bands in Pd40Ni40P20 bulk metallic glass has been compared to an undeformed matrix phase using pair distribution functions (PDFs) derived from energy filtered nanobeam electron diffraction. Shear bands do not show any characteristic contrast in transmission electron microscopy (TEM) images when specimens are prepared with uniform thickness. PDFs from a shear band exhibit a slight decrease in the first peak, indicating a slight difference in packing density and short range order compared to the undeformed matrix.
I. INTRODUCTION
Although metallic glasses exhibit high strength compared to crystalline metals, they lack ductility due to the absence of dislocation activities in an amorphous structure. However, many bulk metallic glasses (BMGs) were found to show certain plasticity by localized shear deformation. BMGs usually fail rapidly along a dominant shear band in tensile loading.1,2 However, in constrained loading geometries like bending,3 rolling, or uniaxial compression,4–6 the formation of multiple shear bands can be triggered, resulting in a significant macroscopic plastic deformation. High plastic strain in some BMGs has been explained by the occurrence of multiple shear banding which is attributed to the presence of mediumrange-order,4 high Poisson’s ratio,5 and structural or chemical inhomogeneities.6 Since the plastic deformation of BMGs is rendered by shear bands, the structure of shear bands has received much scientific interest. Shear bands are usually observed with brighter contrast in bright field TEM images because of preferential milling during specimen preparation procedures.7 A typical bright field image of a
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Address all correspondence to this author. e-mail: [email protected] This paper was selected as an Outstanding Symposium Paper for the 2007 MRS Fall Meeting Symposium Z. DOI: 10.1557/JMR.2009.0001 J. Mater. Res., Vol. 24, No. 1, Jan 2009
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Zr-based amorphous ribbon containing shear bands is shown in Fig. 1. This TEM specimen was prepared by argon ion milling. Early investigations of shear bands in amorphous alloys reported nanocrystallization along the shear bands,8–12 but this feature does not appear in the shear bands of good glass formers like Zr-based or Pd-based metallic glass13 and such example is shown in Fig. 1; therefore, this feature of the shear band is materials dependent. The threshold filtered inverse Fourier transform imaging method using the low angle Fourier transform of high resolution transmission elec
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