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MM: Fachverband Metall- und Materialphysik
MM 7: Microstructure and Phase Transformations II
MM 7.1: Vortrag
Montag, 16. März 2015, 11:45–12:00, H 0106
Shake, rattle and roll! Direct measurement of grain rotations during Ostwald ripening in semisolid Al-5 wt% Cu — Jules Dake1, Jette Oddershede2, Thomas Werz1, Henning Osholm Sørensen3, Søren Schmidt2, and •Carl Emil Krill III1 — 1Ulm University, Germany — 2Technical University of Denmark, Denmark — 3University of Copenhagen, Denmark
Materials scientists studying the coarsening of crystalline solids have long speculated that individual crystallites can undergo rigid-body rotation while shrinking or growing by the usual mechanism of boundary migration. The driving force for such grain rotations would be a reduction in interfacial energy: if two grains rotate toward each other's orientation, the boundary between them will become smaller in angle or even vanish, thereby lowering the free energy of the system. Investigations of spherical grains placed on single-crystalline substrates have lent credibility to this hypothesis; however, it remains to be determined whether grain rotation also takes place under technically relevant conditions, such as the sintering of closely packed powders or the Ostwald ripening of a two-phase material. Employing the recently developed technique of three-dimensional x-ray diffraction (3DXRD) microscopy, we have obtained direct evidence for the occurrence of grain rotations in a bulk, semisolid Al-Cu alloy undergoing Ostwald ripening. Not only did we find that the magnitude of grain rotations increases with relative volume of the liquid phase (as one might naively expect), but we also discovered that the orientation dependence of the interfacial energy biases the direction of rotation.