Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
M: Metallphysik
M 27: Nanoskalige Materialien II
M 27.6: Vortrag
Dienstag, 25. März 2003, 17:45–18:00, IFW D
Influence of Disorder and Energy of Grain Boundaries on the Atomic Dynamics of Nanocrystalline NiHf — •Selcuk Mentese and Jens-Boie Suck — Materials Research and Liquids, Institute of Physics, Technical University Chemnitz, D-09107 Chemnitz, Germany
Several investigations have been performed to study the influence of the large content of grain bondaries in nanocrystalline materials on their thermal and dynamical properties. The nanocrystals used in these experiments had been produced by high energy ball milling or condensation in the gas phase. We have taken advantage of the fact that liquid Ni89 Hf11 can be quenched directly into the nanocrystalline phase by melt spinning forming ribbons of about 40 µm thickness without hydrogen contamination. In chosing the appropriate production parameters one can vary the size and the shape of the nanocrystals. We have used this fact for a comparative study of the atomic dynamics of two different nanocrystalline NiHf samples in the as quenched state and after annealing and a polycrystalline (coarse grained) sample with much less grain boundaries.
From the measured Generalized Vibrational Density Of States (GVDOS) and the dynamic structure factor, determined by neutron inelastic scattering on different time-of-flight spectrometers, we find a rather strong dependence of the low energy atomic dynamics on the relaxational state of the grain boundaries for the first time. This influence seems to be more important than the effect from varying the crystal size (and with this the amount of grain boundaries) mainly considered up to now.