In-Situ Investigation of Local Boundary Migration During Recrystallization
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INTRODUCTION
DURING recrystallization of deformed metals, new nuclei form and grow by boundary migration through the deformed matrix. The velocity, v, of a migrating boundary in response to a driving force, F, is generally expressed by Eq. [1]: v ¼ MF;
½1
where M is the mobility of the boundary.[1] For recrystallization, F is generally considered as the stored energy in the deformed matrix. Many studies have shown that deformation microstructures in most metals are highly heterogeneous[2–4] and that they depend on the crystallographic orientations of the grains present.[5–8] Consequently, F may vary significantly on the local scale. Moreover, the mobility, M, depends on many parameters, including the misorientation of the boundary,[9–11] the boundary plane,[12,13] and the magnitude of the driving force.[14,15] Therefore, despite the simple relationship expressed in Eq. [1], the heterogeneous nature of deformed microstructures, and hence the wide range of values of F and M, suggests that in reality the
YUBIN ZHANG, Researcher, and DORTE JUUL JENSEN, Professor, are with the Danish-Chinese Center for Nanometals, Section for Materials Science and Advanced Characterization, Department of Wind Energy, Technical University of Denmark, Risø Campus, 4000 Roskilde, Denmark. Contact e-mail: [email protected] ANDY GODFREY, Professor, is with the Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, P.R. China. Manuscript submitted September 3, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
migration of recrystallization boundaries is complex, such that the migration possibilities of a recrystallization boundary may vary significantly in space and time. For example, in-situ three-dimensional X-ray diffraction (3DXRD) observations of the growth of a grain during recrystallization have shown that the migration of recrystallization boundaries, even in weakly deformed single crystals, is quite inhomogeneous.[16,17] These measurements have revealed that the migration of individual boundary segments occurs in a jerky stop– go fashion, and that locally fairly large protrusions/ retrusions (i.e., where locally some parts of a boundary segment migrate further/less than the neighboring parts) form and evolve on many boundaries.[16] Recently, ex-situ electron backscatter diffraction pattern (EBSP) investigations have shown that even neighboring boundary segments, with very similar misorientations to the nearby deformed microstructure and with similar driving force (F) from the deformed matrix, can behave quite differently.[18] Subsequent to the publication of the 3DXRD results, theoretical models, aiming at understanding the local boundary migration in terms of the formation of pro-/ re-trusions, have been suggested by Godiksen et al.,[19,20] Martorano et al.,[21,22] and Moelans et al.[23] None of these models are, however, yet able to reproduce and predict typical experimental observations of boundary migration. Experimental ex-situ and in-situ electron channeling contr
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