Experimental Observations of Cylindrical Indentation of a Metallic Glass
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EXPERIMENTAL OBSERVATIONS OF CYLINDRICAL INDENTATION OF A METALLIC GLASS Antonia Antoniou1, S. Bulent Biner1,2 and Ashraf F. Bastawros1 1
Aerospace Engineering and Mechanics, Iowa State University, Ames, IA 50011 Materials and Engineering Physics, Ames Laboratory (USDEO) Iowa State University, Ames, IA 50011
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ABSTRACT In this study, the deformation behavior of a metallic glass under a cylindrical indenter is elucidated with in situ observations. The experimental observations for various indenter radii provide information on both macroscopic and microscopic details of the deformation. The deformation zones developed under indenters with different radii were found to be self-similar, in agreement with the predictions of the cavity expansion model. It will be shown that, the evolution of shear bands under the indenter resembles the solutions obtained from the slip line analysis. Finally, full field strain measurements can provide the detailed information regarding the temporal and the spatial evolution of the shear bands during the course of deformation. INTRODUCTION Bulk metallic glasses have a unique combination of properties such as high strength, large elastic strain limit (up to 2%), corrosion resistance and formability [1]. The nucleation and growth the shear bands before the onset of the failure is the main characteristic of the inhomogeneous deformation mode. The evolution of shear bands is usually more clearly seen in confined deformations such as in bending [2], notched samples [3] and indentation [4-7]. We developed an experimental technique [8] which yields information not only the force-displacement response of the material but also enables us to survey the evolution of the deformation in time and space. The recorded images can be further processed into in-plane strain maps, yielding more details on the embryonic stages of the shear bands during the course of deformation. EXPRERIMENT DETAILS The metallic glass used in this study was Zr 41.2–Ti 13.8–Cu 12.5–Ni 10-Be 22.5 (Vitreloy-1). TEM and X-ray diffraction studies both showed that the material is in amorphous state. The
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dimensions of the samples were 3x7x15mm. The sample surfaces were polished with standard metallographic techniques to 1µm finish prior to the indentation experiments. Special care was taken such that the surfaces remained orthogonal during polishing. The general properties of Vitreloy-1 can be found in ref [1]. Four different indenter radii were used (0.4, 0.8, 1.6 and 2.4mm) for these experiments. The indenter was made of silicon carbide. The alignment of the indenter and the sample was crucial and a fixture was devised that ensured the line of contact of the indenter and sample was perpendicular to the front plane of the sample. This would ascertain that any bands appearing on the front surface are not emanating at an oblique angle. At least three tests were performed for each indenter radii.
RESULTS The macroscopic response of the cylindrical indentations with varying indenter radii can be seen in
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