Mapping the Strain Distributions in Deformed Bulk Metallic Glasses Using Hard X-Ray Diffraction
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COMPARED with crystalline counterparts, bulk metallic glasses (BMGs) have some superior properties, such as high yield strength, hardness, large elastic limit, high fracture toughness, and corrosion resistance, and hence are considered as promising engineering materials.[1,2] However, the poor plasticity and low fatigue resistance restrict their wider exploitation in engineering applications.[3,4] High-energy X-ray diffraction (XRD) has proven to be a suitable tool to describe the local atomic structure of the metallic glasses.[5] Poulsen et al. have demonstrated that the strain tensor of bulk metallic glasses can be quantitatively estimated by this technique[6]. Hufnagel et al. reported that the strain values in a metallic glass measured by XRD are in good agreement with macroscopic observations of their elastic behavior.[7] Furthermore, in situ diffraction measurements were carried out for Cu-Zr-Al and Zr-Cu-Ni-Al BMGs in compression[8] or tension.[9,10] Many experimental results show that the pressure dependence of flow and fracture in metallic glasses exhibits tension-compression asymmetry.[3,11,12] Metallic glasses are generally stronger in compressive loading than in tension. Bending is a J. BEDNARCIK, Postdoctor, and H. FRANZ, Group Leader PETRA III Experiments, are with the Deutsches Elektronen-Synchrotron DESY, 22603 Hamburg, Germany. Contact e-mail: jozef.bednarcik@ desy.de L.Y. CHEN and X.D. WANG, Postdoctors, are with the International Center for New-Structured Materials ICNSM, Zhejiang University, Hangzhou 310027, P.R. China, and are also with the Laboratory of New-Structured Materials, Department of Materials Science and Engineering, Zhejiang University. J.Z. JIANG, Group Leader, is with the International Center for New-Structured Materials ICNSM, Zhejiang University, also with the Laboratory of NewStructured Materials, Department of Materials Science and Engineering, Zhejiang University, and is also with the School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, P.R. China. Manuscript submitted February 15, 2011. Article published online March 7, 2012 1558—VOLUME 43A, MAY 2012
special case of deformation, which allows inducing a spatial distribution of tensile/compressive stresses inside a single piece of a material. Hence, the single piece of a material can be used for study of simultaneous action of the tensile/compressive forces. Inoue et al.[13,14] found that significant bend ductility may be achieved only if the sample dimension is below a critical value, suggesting a size effect for bend ductility. Conner et al. found that the shear band spacing in metallic glass plates subjected to bending scales with plate thickness and that the bend ductility increases dramatically with decreasing plate thickness.[15,16] When bending Cu-Zr-Al-Ti bulk metallic glass, Chen et al. observed that the real hardness decreases with pre-existing tensile stress, but does not increase obviously with preexisting compressive stress. The main objective of this work is to follow the st
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