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MM: Fachverband Metall- und Materialphysik

MM 31: Mechanical properties II - Characterisation mechanics

MM 31.2: Talk

Tuesday, April 1, 2014, 16:00–16:15, IFW D

Observation of dislocation - related damping mechanisms in Al - based materials — •Jens Bernhardt and Hans-Rainer Sinning — Institut für Werkstoffe, Technische Universität Braunschweig, Germany

Damping features in Al based alloys between 100 K and room temperature are due to dislocation dynamics. In metal matrix composites (MMCs) formation of micro plastic deformation zones take place during thermal cycling at the interface between metal matrix and reinforcing phase. As we have shown before a broad damping structure in mechanical loss spectra of annealed AA 6061 based MMC (22 % Al2O3) could be assigned to free dislocations generated at the interface between metal matrix and reinforcing particles.

To understand the nature of this broad damping structure we measured damping spectra of Al(99,99), and an Al(99,7) + 10 % B4C composite. In deformed Al(99,99) we observed the Bordoni-Peak around 150 K at 1 kHz. This peak is due to interaction of dislocations with crystal lattice. In Al(99,7) + 10 % B4C a further peak in damping was observed at temperatures between 250 K and room temperature. He is embedded in a broad damping structure comparable to the one observed in AA 6061 + 22 % Al2O3. The mechanism of this peak is most likely dragging of dislocations by point defects (PD) with some enhanced diffusion involved. We will show that this damping peak is depending on heating rate, amplitude of measurement and frequency as well. Properties of Bordoni-Peak, PD-Dislocation Peak and also of the broad damping structure are being discussed for all materials.