Five-Parameter Grain Boundary Inclination Recovery with EBSD and Interaction Volume Models
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INTRODUCTION
GRAIN boundaries have a significant effect on material properties. Depending on the interfacial energies of the boundaries, the presence of certain types of grain boundaries can either assist or degrade several material behaviors and properties (e.g., creep, corrosion, precipitation of solute atoms, and electrical or thermal conductivity). This energy at the boundary is partially dependent on the grain boundary’s inclination.[1] Electron backscatter diffraction (EBSD) has been useful in boundary characterization because of its ability to identify grain orientations and the misorientation angle between points on either side of a grain. Coincident site lattice (CSL) theory has been used extensively with EBSD scans to identify grain boundary types with favorably low interface energies without knowledge of the grain boundary plane inclination.[2–4] However, the true coherence and beneficial nature of such boundaries is also significantly influenced by the grain boundary plane normal.[5] In order to also recover the full five-parameter grain boundary character[6] of a material (three variables for a grain orientation, and two for the grain boundary plane normal) using EBSD, one currently must use focused ion beam (FIB), manual serial sectioning, or stereolCAROLINE SORENSEN, Undergraduate Student, formerly with the Department of Mechanical Engineering, Brigham Young University, Provo, UT, is now with MIT, Cambridge, MA. JOHN A. BASINGER, PhD Student, formerly with the Department of Mechanical Engineering, Brigham Young University, is now with Southwest Research Institute, San Antonio, TX. MATTHEW M. NOWELL, Senior Scientist, is with the TSL-EDAX/AMETEK, Draper, UT. DAVID FULLWOOD, Associate Professor, is with the Department of Mechanical Engineering, Brigham Young University. Contact e-mail: [email protected] Manuscript submitted May 29, 2012. Article published online June 11, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
ogy[7] to reconstruct the full 3D grain boundary character. Unfortunately, these techniques are destructive to the material and prohibit in situ experiments. Synchrotron-based X-ray diffraction and imaging techniques can access orientation as well as 3D grain shape non-destructively for a recovery of the full grain boundary character.[8] The spatial resolution of this approach is limited to the micrometer scale (vs tens of nanometers in EBSD). Here, a technique is presented for the non-destructive determination of grain boundary plane normals (and orientations) using the saved EBSD images from a single OIM scan. EBSD images result from the diffraction of electrons that are scattered out of the sample from within a 3D volume, called the electron interaction volume. Information regarding the crystal structure that is extracted from these images (such as orientation) is typically treated as 2D data. In the case where the interaction volume contains more than one lattice configuration, the indexing software (in this case, OIMä) decodes only the structure with the stronger pattern. The other structure’
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