Viewpoint on the Formation and Evolution of Annealing Twins During Thermomechanical Processing of FCC Metals and Alloys
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Viewpoint on the Formation and Evolution of Annealing Twins During Thermomechanical Processing of FCC Metals and Alloys NATHALIE BOZZOLO and MARC BERNACKI The question of the formation mechanism of annealing twins in face-centered cubic metals and alloys, which is still not resolved in spite of the fact that the existence of these defects is known for long, is addressed in this paper. The different mechanisms proposed through the years are reviewed. Most of them focus on coherent twin boundaries. However, incoherent twin boundaries are very frequent as well, notably in recrystallized microstructures and would definitely deserve more specific attention. Twin topologies are so much different after recrystallization and after grain growth that distinct names would be better suited than the general term of annealing twins. Because twins are at the core of most grain boundary engineering approaches, the mechanisms by which an interconnected network of twin and related boundaries can be formed are discussed, in the light of the current knowledge on annealing twin formation mechanisms. Finally, the state of the art of mesoscopic models and simulations able to account for twin boundaries is presented. Accounting for twins is a requirement since they not only play a role in microstructure evolution upon thermomechanical processing but also affect the in-service material behavior, positively or negatively depending on the involved properties. https://doi.org/10.1007/s11661-020-05772-7 The Minerals, Metals & Materials Society and ASM International 2020
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INTRODUCTION
ANNEALING twins are known since long to be very common in Face-Centered Cubic (FCC) metals and alloys with low-to-medium stacking fault energy, but, quite surprisingly, the exact mechanisms by which they appear and evolve during thermomechanical processing remain poorly understood. One reason might be that the term annealing twins is too general, and actually covers different types of twins arising by distinct mechanisms. As pointed out already 70 years ago, annealing twin formation is a process that accompanies grain boundary migration.[2] But there are several mechanisms by which grain boundaries may migrate during annealing, the two main ones being (i) the migration of a recrystallization front driven by the consumption of the energy stored in the form of defects (mostly dislocations) induced by [1]
NATHALIE BOZZOLO and MARC BERNACKI are with the MINES ParisTech, PSL Research University, CEMEF - Centre de mise en forme des mate´riaux, CNRS UMR 7635, CS 10207, rue Claude Daunesse, 06904, Sophia Antipolis Cedex, France. Contact e-mail: [email protected] Manuscript submitted January 6, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
plastic deformation, and (ii) the migration of a grain boundary to reduce its curvature or to adopt a lower energy plane, within the so-called grain growth regime, with no stored energy involved. In his early paper, Burke[2] reported that annealing twins are prominent after recrystallization and that «the twins f
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