Dresden 2011 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 29: Topical Session TEM VIII

MM 29.4: Vortrag

Mittwoch, 16. März 2011, 16:30–16:45, IFW B

Diffraction spots off the diffraction rings in severely deformed bulk nanocrystalline FeAl — •Anna Findeisen, Christoph Gammer, Christian Rentenberger, and Hans-Peter Karnthaler — University of Vienna, Physics of Nanostructured Materials, Boltzmanngasse 5, 1090 Wien, Austria

The bulk intermetallic compound FeAl (processed with high purity Fe and Al) is made nanocrystalline by severe plastic deformation (SPD) applying the method of repeated cold rolling and folding. For the transmission electron microscopy (TEM) study thin foils were prepared by ion milling. TEM shows in the nanocrystalline structure grain sizes <100 nm. As expected the electron diffraction patterns show diffraction rings due to the different orientation of the nanograins. In addition to the diffraction spots lying on the rings, several spots are encountered that lie clearly off the rings. The TEM study reveals that these additional spots are not arising by an epitaxial oxide or other components. The analysis leads to the clear result that these spots are caused by moiré effects since their diffraction vectors can be constructed by adding the vectors of appropriate spots on the rings. Moiré effects are expected to occur in TEM of bulk nanocrystalline materials when the grain size is small and especially when the density of subgrainboundaries is high. The latter is confirmed by the fact that the occurrence of additional spots is more pronounced in the present case than in materials made nanocrystalline by other SPD methods. It also agrees with the results of differential scanning calorimetry showing in the present study higher values of enthalpies connected with the different peaks.