Volume 47, Issue 11

An analytical distribution function characterising the grain sizes of polycrystalline microstructures is presented. Contrary to standard mathematical probability functions that are still often used for description of experimentally obtained size distributions, this one is based on a statistical mean-field theory of grain growth and is fully consistent with the fundamental physical conditions of total-volume conservation and the existence of a finite average grain volume. It is found that this distribution function describes the grain size distribution obtained by Monte Carlo Potts model simulations better than standard mathematical distributions. Additionally, two-dimensional plane sections from the simulated three-dimensional grain structures are considered and compared with experimental data, and the analytic size distribution function is also compared with an experimental grain size distribution for pure iron obtained by serial sectioning.

Kurzfassung Die Darstellung des Gefüges von Aluminiumlegierungen bereitet immer wieder Probleme. So kommt es z.B. häufig zu Fehlinterpretationen bei der Unterscheidung von Korngrenzen und Subkorngrenzen wegen deren unterschiedlichen Reaktionen auf die verschiedenen möglichen Ätzmittel. Aber auch die Vorbereitung durch Schleifen und Polieren kann bei nur wenig veränderten Randbedingungen zu unterschiedlichen Ergebnissen nach dem Ätzvorgang führen. In den hier beschriebenen Untersuchungen wurden die Aluminiumlegierung EN AW-6061 und zwei Aluminiummatrix-Verbundwerkstoffe auf Basis von EN AW-6061 mittels Rückstreuelektronen-Kikuchi Beugung (EBSD; electron back scattering diffraction) untersucht. Es konnte eine eindeutige Zuordnung von Groß- und Kleinwinkelkorngrenzen vorgenommen werden. So gelang eine genaue Analyse des Gefüges sowohl hinsichtlich des Einflusses der Fertigung als auch der Verstärkungsphase in den Verbundwerkstoffen.

The phases obtained in copper aluminium bronze alloy (Cu-Al10-Fe2) cast into a permanent die were investigated. The parameters examined were the pre-heating temperatures of the die and the graphite coating thickness. The phases α and γ2 were detected as well as the metastable phases β’ and γ’. The intermetallics of the system Fe-Al were obtained in various stoichiometric compositions. The different cooling rates of the casting resulted in two mechanisms of transformation to α grains out of the unstable β phase, one being nucleation and growth producing needle shaped α grains, the other exhibiting a massive transformation to spherical α grains. These two mechanisms determine the changes in the size of the α grains as a result of changes in the cooling rate in its various ranges.