Browsing by Author "Kauffmann, A."
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- ItemGrain refinement and deformation mechanisms in room temperature severe plastic deformed Mg-AZ31(Basel : MDPI AG, 2013) Knauer, E.; Freudenberger, J.; Marr, T.; Kauffmann, A.; Schultz, L.A Ti-AZ31 composite was severely plastically deformed by rotary swaging at room temperature up to a logarithmic deformation strain of 2.98. A value far beyond the forming limit of pure AZ31 when being equivalently deformed. It is observed, that the microstructure evolution in Mg-AZ31 is strongly influenced by twinning. At low strains the [formula presented] twin systems lead to fragmentation of the initial grains. Inside the primary twins, grain refinement takes place by dynamic recrystallization, dynamic recovery and twinning. These mechanisms lead to a final grain size of ≈ 1 μm, while a strong centered ring fibre texture is evolved.
- ItemMicrostructure evolution during annealing of an SPD- processed supersaturated Cu – 3 at.% Ag alloy(Bristol : IOP Publishing, 2014) Gubicza, J.; Hegedűs, Z.; Lábár, J.L.; Sarma, V.S.; Kauffmann, A.; Freudenberger, J.Supersaturated Cu-3 at.% Ag alloy was processed by rolling at liquid nitrogen temperature and subsequent annealing at 623 K up to 20 min. It was found that after annealing, an inhomogeneous solute atom distribution developed, since the Ag particles with small size and/or large specific interfacial energy were dissolved due to the Gibbs-Thomson effect. In the region where the solute concentration increased, a high dislocation density was retained in the Cu matrix even after annealing, while in the region where the Ag solute content did not increase, the dislocation density decreased by more than one order of magnitude. Therefore, in the cryorolled and annealed samples, heterogeneous microstructures were developed where both the dislocation density and the solute concentration varied considerably.
- ItemProcessing of intermetallic titanium aluminide wires(Basel : MDPI AG, 2013) Marr, T.; Freudenberger, J.; Kauffmann, A.; Romberg, J.; Okulov, I.; Petters, R.; Scharnweber, J.; Eschke, A.; Oertel, C.-G.; Kühn, U.; Eckert, J.; Skrotzki, W.; Schultz, L.This study shows the possibility of processing titanium aluminide wires by cold deformation and annealing. An accumulative swaging and bundling technique is used to co-deform Ti and Al. Subsequently, a two step heat treatment is applied to form the desired intermetallics, which strongly depends on the ratio of Ti and Al in the final composite and therefore on the geometry of the starting composite. In a first step, the whole amount of Al is transformed to TiAl3 by Al diffusion into Ti. This involves the formation of 12% porosity. In a second step, the complete microstructure is transformed into the equilibrium state of γ-TiAl and TiAl3. Using this approach, it is possible to obtain various kinds of gradient materials, since there is an intrinsic concentration gradient installed due to the swaging and bundling technique, but the processing of pure γ-TiAl wires is possible as well.
- ItemTwinning phenomena along and beyond the bain path(Basel : MDPI AG, 2013) Kauffmann-Weiss, S.; Kauffmann, A.; Niemann, R.; Freudenberger, J.; Schultz, L.; Fähler, S.Twinning is a phenomenon that occurs, e.g., during deformation, martensitic transformation and film growth. The present study shows that the crystallography of twinning can be described by two twinning modes along the complete Bain transformation path and beyond connecting body-centered and face-centered cubic structures. To probe this concept, we used strained epitaxial films of the Fe-Pd magnetic shape memory system. As the substrate acts as an absolute reference frame, we could show by pole figure measurements that all observed twinning can be a body-centered and face-centered cubic twinning mode. This continuously transforms towards identity when approaching the complementary structure.