Insights from the Lattice-Strain Evolution on Deformation Mechanisms in Metallic-Glass-Matrix Composites
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BULK metallic glasses (BMGs) exhibit many desirable properties, e.g., high strengths and hardness, large elastic limits, and excellent corrosion and oxidization resistance,[1–7] which make them potential candidates as new structural materials. However, BMGs are notorious for their brittle nature upon loading due to the formation of the highly localized shear bands. In a monolithic BMG, a major shear band will run through the entire sample once it initiates from some weak locations. To circumvent this disadvantage, a class of metallic-glassmatrix composites (MGMCs), with ductile dendritic crystalline phases dispersed in the metallic-glass (MG) matrix, has emerged with improved toughness, due to the stabilization against shear localization and propagation of critical shear bands upon loading.[8–13] The primary objective will be clearly directed to how to design such a microstructure and control the internal
H.L. JIA, L.L. ZHENG, and W.D. LI, Research Assistants, G.Y. WANG, Research Associate, and P.K. LIAW, Professor, are with the Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996. N. LI, Research Assistant, is with the School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, P.R. China. J.W. QIAO, Professor, is with the College of Materials Science and Engineering, Taiyuan University of Technology, Shanxi 030024, P.R. China. Y. REN, Beam Scientist, is with the X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439. YANFEI GAO, Associate Professor, is with the Department of Materials Science and Engineering, University of Tennessee, and also with the Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831. Contact e-mail: [email protected] Manuscript submitted April 4, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
strain fields so that the ductility enhancement can be manipulated. A number of studies have been conducted to investigate the deformation mechanisms in the dendrite-dispersed MGMCs. For example, Hofmann et al.[10] and Qiao et al.[8,9,14–16] found that the MGMCs had substantially improved malleability and tensile ductility compared with monolithic BMGs, presumably by blocking the propagation of shear bands by soft crystalline phases in MGMCs under loading.[10,17,18] This mechanism can be revealed by post-mortem observations, while only limited in situ studies have been performed by synchrotron X-ray and neutron diffraction measurements on the microstructural origin of these deformation mechanisms.[19–23] We note that the synchrotron X-ray diffraction measurement has unique advantages, compared with the neutron diffraction in respect of resolution, which tends to be more sensitive to structural disorder and fluctuations, and allows the background intensities between peaks to be estimated more reliably.[24] In the X-ray diffraction, lattice strain can be calculated from the shift of diffraction peaks, which corresponds to the elastic lattice distortion of grains in different crystal
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