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MM: Fachverband Metall- und Materialphysik

MM 26: Poster Session

MM 26.76: Poster

Dienstag, 23. März 2010, 14:45–16:30, Poster C

Is abnormal growth actually the norm in nanocrystalline materials? — •Jules M. Dake, Heiko Paul, and Carl E. Krill III — Institute of Micro and Nanomaterials, Ulm University, Ulm, Germany

Nanomaterials may enjoy a privileged place in the fantasies of science-fiction writers, but among researchers studying the phenomenon of grain growth, nanocrystalline specimens suffer from a decidedly dodgy reputation. Not only do they generally contain significant impurity levels (though not necessarily much higher than those of conventional samples, when normalized to the total area of grain boundaries), but experiments designed to pin down characteristic parameters like the growth exponent or activation enthalpy for boundary migration are disappointingly inconsistent. Add to this the suspicion that microstructural entities like triple junctions or quadruple points could modify the kinetics of boundary migration for nanosized grains, and you have a recipe for chaos! To cut through this fog, we carried out a systematic study of isothermal grain growth in nanocrystalline Fe using high-temperature x-ray diffractometry—only to be confronted by indirect evidence for the evolution of grain-size distributions in a manner reminiscent of abnormal grain growth. In order to quantify the microstructural inhomogeneity directly and, thereby, clarify the origins of the x-ray results, we subjected select samples at various stages of annealing to microscopic study using EBSD and TEM. The results indicate that it will not be easy to pin the blame for abnormal growth in nanocrystalline Fe on the usual suspects, like precipitates or texture effects.