Measuring Grain Boundary Character Distributions in Ni-Base Alloy 725 Using High-Energy Diffraction Microscopy
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NTRODUCTION
CERTAIN behaviors of polycrystalline materials are governed by grain boundaries (GBs). Examples include grain growth,[1] plastic deformation,[2,3] fracture,[4] oxidation,[5] corrosion,[6] and creep.[7] Since GBs exhibit a wide variety of structures and properties, it has become important for metallurgists to know the distribution of GB types in polycrystalline solids. In this work, we use high-energy X-ray diffraction microscopy (HEDM)[8] to characterize the grain boundary crystallographic character distribution in Ni-base alloy 725: a material developed for use in highly corrosive environments.[9]
AKBAR BAGRI, Postdoctoral Associate, and SILVIJA GRADEC˘AK, Professor, are with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139. Contact e-mail: Akbar_Bagri@alumni. brown.edu JOHN P. HANSON, PhD Student, is with the Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. JONATHAN LIND, PhD Student, and ROBERT M. SUTER, Professor, are with the Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213. PETER KENESEI, Beamline Scientist, is with the X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439. MICHAEL J. DEMKOWICZ, Associate Professor, is with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, and also with the Department of Materials Science and Engineering, Texas A&M University, College Station, TX 77843. The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (‘‘Argonne’’). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract no. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. Manuscrtipt submitted March 4, 2016. Article published online October 25, 2016 354—VOLUME 48A, JANUARY 2017
Absorption of hydrogen from an acidic environment into high-strength alloys may result in loss of ductility.[10–12] Brittle fracture of materials, especially those operating in harsh conditions, often occurs along grain boundaries and sometimes leads to unexpected failure. Information about the distribution of grain boundary types in the alloy may lead to improved lifetime predictions and the design of materials with reduced susceptibility to environmental degradation. A full description of the state of a given GB requires five macroscopic parameters that describe the crystallography of the boundary as well as a much larger number of parameters detailing its microscopic state. In the present work, we focus on just the five crystallographic parameters:[13] three rotation angles to describe the misorientation between the two crystals that form the boundary and two spherical angles that specify the orientation of
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