Grain Size, Misorientation, and Texture Evolution of Copper Processed by Equal Channel Angular Extrusion and the Validit
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WHEN the average crystal size of a material is smaller than 1 lm, methods involving electron microscopy or X-ray diffraction (XRD) are used to quantify grain size. Although these techniques do not necessarily return the same results, they complement each other and enable a better understanding of microstructural peculiarities. Using a high resolution (HR) scanning electron microscope (SEM) equipped with a field emission gun (FEG) and newly developed automated processes for electron backscatter diffraction (EBSD), large area scans are possible for materials having grain sizes lower than FLORIAN H. DALLA TORRE, Postdoctor, is with the Department of Materials Engineering, Monash University, Victoria 3800, Australia. and the Laboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland. Contact e-mail: fl[email protected] AZDIAR A. GAZDER, PhD Student, CHENG F. GU, Research Assistant, CHRISTOPHER H.J. DAVIES, Associate Professor, is with the Department of Materials Engineering, Monash University, and the Victorian Centre for Advanced Materials Manufacturing, Victoria, Australia and ELENA V. PERELOMA, Professor, is with the Department of Materials Engineering, Monash University, the Victorian Centre for Advanced Materials Manufacturing, Victoria, and with the BlueScope Steel Metallurgy Centre, School of Mechanical, Materials and Mechatronics Engineering, Faculty of Engineering, University of Wollongong, Wollongong, Australia. Manuscript submitted February 24, 2006. Article published online May 12, 2007. 1080—VOLUME 38A, MAY 2007
500 nm. Compared to transmission electron microscopy (TEM), EBSD returns significantly improved microstructural statistics. Consequently, the latter technique has been successfully applied to heavily deformed metals with grain sizes less than a micrometer.[1,2] Below 100 nm, grain size indexing becomes difficult using EBSD. Thus, XRD peak broadening analysis is favored where high statistical grain size measurements are deduced from scans on areas several square millimeters in size. This is often coupled with direct grain size measurements by TEM. The combination of TEM and X-ray techniques yields a clearer interpretation of the coherently scattered domains.[3] Furthermore, the advantage of TEM lies in its capability to reveal misorientation relationships via tilting experiments in microdiffraction. Although such experiments have been used to characterize heavily deformed metals,[4,5] they are also tedious and time consuming. In a fine-grained material with a homogeneous microstructure composed of random high-angle grain boundaries (HAGBs), grain size comparisons obtained by EBSD and TEM or XRD peak broadening analysis have shown close agreement.[1,6] However, in a material subjected to equal channel angular extrusion (ECAE), the microstructure is often inhomogeneous and consists not only of grains confined by HAGBs, but is also characterized by different dislocation substructures. These microstructural variations can therefore provide different siz
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