In-situ TEM investigation of deformation behavior of metallic glass pillars
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1185-II11-03
In-situ TEM investigation of deformation behavior of metallic glass pillars C.Q. Chen, Y.T. Pei, J.Th.M. De Hosson∗
Department of Applied Physics, Materials Innovation Institute M2i, University of Groningen, Nijenborgh 4, 9747 AG Groningen, the Netherlands
ABSTRACT We show results of in situ TEM (transmission electron microscope) quantitative investigations on the compression behaviors of amorphous micropillars fabricated by focused ion beam from Cu47Ti33Zr11Ni6Sn2Si1 metallic glass (MG) ribbon. Pillars with well defined gauge sections and tip diameter ranging from 100 nm to 640 nm are studied. Quantitative compression tests were performed by a recently developed Picoindenter TEM holder, with the evolution of individual shear bands monitored in real time in TEM. It is found that the deformation of the MG pillars at the present size domain is still dominated by discrete shear banding as demonstrated by intermittent events in the load-displacement curves. However, the frequency, amplitude and distribution of these shear banding events are clearly size-dependent at submicrometer scale, leading to an apparently transition in deformation mode from highly localized inhomogeneous deformation to less localized and more distributed deformation with decreasing pillars diameter. Deformation of a 105 nm diameter pillar having rounded tips is characterized with fully homogeneous bulge at the initial stage of deformation, indicating prompting effect of multi-axial stress state on transition to fully homogeneous deformation.
INTRODUCTION Despite the high yield strength, monolithic metallic glass suffers from highly localized shear deformation at ambient temperature and therefore exhibit very limited ductility [1-3], with the process of initiation and evolution of shear bands still puzzling [3]. Study of the deformation behavior of small volume metallic glass is an interesting route for the exploration of the initiation and evolution of individual shear bands and it has attracted a rapid increasing interest over recent years [4,5,6,7,8,9,10,11]. It also has practical significance on the design of recently booming metallic glass based composites [12] or multilayers [13], which is effective in improving the ductility but needs understanding in shear localization that is constrained by size. Various hints in deformation mechanism of small volume metallic glasses appeared suggesting either improved ductility [4,5 ,11] or increased yield strength at small scales [6,7,8,9,10]. However, due to technical difficulties, the information obtained is limited by a lack of either quantitative stress∗
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strain information [4] or a capability of monitoring the evolving deformation structure [5,6,7,8,9,10], as well as by the limited range of examined specimen sizes. We report here quantitative in-situ TEM microcompression of metallic glass pillars with diameters ranging from 640 nm down to 105 nm, with new insights into size-eff
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