Papers by Author: Günter Gottstein

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Authors: Christoph Günster, Dmitri A. Molodov, Günter Gottstein
Abstract: The results of investigations of magnetically driven grain boundary migration in high purity (99.995%) zinc bicrystals are presented. In-situ measurements were conducted by means of a specially designed and fabricated polarization microscopy probe. The migration of planar tilt grain boundaries with various misorientation angles in the range between 60° and 90° was studied. The absolute grain boundary mobility and its temperature dependence was measured in the regime between 330°C and 415°C and the corresponding migration activation parameters were determined. The results revealed that there is a pronounced misorientation dependence of grain boundary mobility in the investigated angular range. The migration activation enthalpy was found to vary between 1.18 eV and 2.15 eV. The obtained activation parameters comply with the compensation law, i.e. the migration activation enthalpy changes linearly with the logarithm of the pre-exponential factor.
Authors: Tatiana Gorkaya, Thomas Burlet, Dmitri A. Molodov, Günter Gottstein
Abstract: A novel set-up developed to continuously observe and measure stress driven grain boundary migration is presented. A commercially available tensile/compression SEM unit was utilized for in-situ observations of mechanically loaded samples at elevated temperatures up to 850°C by recording orientation contrast images of bicrystal surfaces. Two sample holders for application of a shear stress to the boundary in bicrystals of different geometry were designed and fabricated. The results of first measurements are presented.
Authors: Günter Gottstein
Abstract: A new approach to dynamic recrystallization (DRX) is introduced. It is based on the assumption that the critical conditions for DRX and the arrest of DRX grain boundaries are related to the development of mobile subboundaries. The theoretical predictions are compared to experimental results during incipient and steady-state DRX. The grain size sensitivity of the DRX grains establishes the desired link between deformation and DRX microstructure.
Authors: Dirk M. Kirch, A. Ziemons, I. Lischewski, Dmitri A. Molodov, Günter Gottstein
Abstract: A novel high temperature heating method in combination with automated EBSD-data acquisition is presented. A commercially available infrared laser is utilized to heat samples up to a temperature of about 1000°C in high vacuum in a SEM while acquiring EBSD-data of the microstructure. First results on the γ-α-γ phase transformation between 840°C and 865°C in a microalloyed ferritic low carbon steel is presented.
Authors: Manfred Schneider, Günter Gottstein, L. Löchte, Jürgen Hirsch
Authors: Olga Sukhopar, Günter Gottstein
Abstract: In the current study the nucleation of Cube grains during recrystallization in a commercial Al-Fe-Si alloy was investigated by in-situ and ex-situ annealing experiments at different temperatures. Both methods confirm that the Cube grains can be nucleated during RX both at large deformed Cube bands and other locations. During annealing only about one third of the Cube nuclei from these other locations developed into Cube oriented recrystallized grains owing to an unfavorable growth environment. Such nuclei needed also a longer incubation time due to their small size compared to nuclei formed at large Cube bands which can form nuclei very fast owing to the well-developed substructure and transition zones promoting nucleation. The growth rate of all Cube nuclei was found to be strongly influenced by their environment. This effect became more pronounced with decreasing annealing temperature due to an increasing amount of recovery.
Authors: Dmitri A. Molodov, U. Czubayko, Günter Gottstein, Lasar S. Shvindlerman
Authors: Jürgen Hirsch, Günter Gottstein, Markus Büscher, Christian Leroy, Andrew Green
Authors: Xenia Molodova, Günter Gottstein
Abstract: In the present study the microstructure evolution of the aluminum alloy 3103 subjected to ECAP up to eight passes applying route Bc was investigated after deformation and subsequent isothermal annealing. The deformed and annealed states were analyzed by SEM, EBSD, optical microscopy and microhardness tests. It will be demonstrated that this ECAP deformed material shows an increased stability against discontinuous recrystallization with growing number of passes.
Authors: E. Jannot, Volker Mohles, Günter Gottstein, B. Thijsse
Abstract: Activation energies for solute diffusion along dislocations are difficult to measure experimentally. The aim of this work is to provide insight into pipe diffusion with the help of atomistic simulations. The distribution of vacancy formation energy and the activation energy for copper migration are determined in the core of an edge dislocation in aluminum. The Dimer method is used to find activation energies for vacancy migration. The activated region around the dislocation where a very high diffusivity is observed and the activation energy for copper diffusion associated with this region are interpreted with regard to the contribution of the dislocation and the contribution of the alloying.
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