Regensburg 2004 – wissenschaftliches Programm
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M: Metallphysik
M 23: Hauptvortrag Dieter Brunner
M 23.1: Hauptvortrag
Donnerstag, 11. März 2004, 09:30–10:00, H16
Plasticity in body-centred cubic structures with emphasis on low-temperature behaviour — •Dieter Brunner — Max-Planck-Institut für Metallforschung, Heisenbergstrasse 3, 70569 Stuttgart
Materials crystallizing in the body-centred cubic (bcc) structure exhibit plastic behaviour which differs impressively from that of differently structured materials. The different behaviour is related to different slip and work hardening mechanisms. The dependence of the yield stress on temperature, strain-rate, and both the concentration and configuration of atomic lattice defects is very pronounced in contrast to fcc materials. These differences are particularly large in the low-temperature regime below a characteristic temperature TK. At low temperatures, high purity and sufficiently small sample dimensions are prerequisites for tensile tests. In the talk, relevant results of measurements with single crystals of the metals α-Fe, Mo, W, Nb, Ta, the intermetallic alloy NiAl, the alkali metal potassium, and the oxide ceramic SrTiO3 will be addressed. The crucial point in the interpretation of the plasticity of bcc metals, for example, is based on <111>a0/2 screw dislocations whose motion governs the plastic behaviour and which possess a non-planar core structure. Accordingly, they are rather sessile but can be moved by thermally activated kink-pair formation on screw dislocations. Seeger’s kink-pair theory developed in the 1980s has proved to be in excellent agreement with the experimental results. Applying this model enables the macroscopic behaviour to be described in terms of few kink parameters that can be determined from deformation experiments for the above mentioned materials.