Regensburg 2007 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

MM: Fachverband Metall- und Materialphysik

MM 12: Growth

MM 12.3: Vortrag

Montag, 26. März 2007, 16:45–17:00, H6

In situ investigation of Ostwald ripening in Al-Cu alloys by x-ray microtomography — •Mehdi Lalpoor¹, Lukas Helfen², and Carl Krill¹ — ¹Institute of Micro and Nanomaterials, Ulm University, D-89081 Ulm — ²Institut für Synchrotronstrahlung (ISS/ANKA), Forschungszentrum Karlsruhe, D-76021 Karlsruhe

Conventional methods for studying Ostwald ripening in multiphase alloys rely on the characterization of planar sections, which provide access to statistically averaged microstructural parameters but not to local quantities, like the actual 3D shapes of individual particles. Serial sectioning can capture the 3D microstructure of solid specimens, but it destroys them in the process, rendering the procedure unsuitable for in situ coarsening studies. In contrast, x-ray microtomography delivers 3D microstructural data in a nondestructive manner, thus providing a way to track sample evolution over time. We report a first application of this approach to Ostwald ripening occurring in the model system Al-6.7 wt% Cu above its eutectic temperature. A temporal sequence of absorption-contrast tomographic images reveals the growth/shrinkage of solid α-Al particles embedded in a liquid phase richer in Cu. Microstructural evolution is found to be a superposition of coarsening-driven migration of phase boundaries and gravity/thermal gradient-driven vertical displacement. Quantitative values for local and global coarsening rates are extracted via image segmentation and combined with the results of conventional 2D studies to obtain additional insight into the influence of the volume fraction of the coarsening phase on the kinetics of Ostwald ripening in this system.