Papers by Author: László S. Tóth

Abstract: In the present study, the effects of kinematic and geometric asymmetries in rolling during multi-pass processing of IF steel are examined. The theoretical investigation by final element simulations and experimental investigations by means of electron-backscatter diffraction analysis and tensile tests suggest that asymmetric rolling increases the total imposed strain compared to symmetric rolling, and largely re-distributes the strain components due to additional shear. This enhances the intensity of grain refinement, strengthens and tilts crystallographic orientations, and increases mechanical strength. The effect is highest in the asymmetric rolling with differential roll diameters.

Abstract: A comparative experimental and simulation study of oxygen-free high conductivity copper produced by equal channel angular pressing (ECAP) one-pass has been carried out by using electron backscatter diffraction (EBSD) and a recently proposed grain refinement model. The grain size and misorientation distributions were extracted from the EBSD measurements. It was found that the microstructure in the ECAP deformed copper was much more refined on the TD plane. The grain size observed experimentally can be fairly well predicted by the grain fragmentation model.

Abstract: As-received hot-rolled 5.6 mm thick IF steel sheet was symmetrically/asymmetrically cold rolled at room temperature down to 1.9 mm. The asymmetric rolling was carried out in monotonic (an idle roll is always on the same side of the sheet) and reversal (the sheet was turned 180º around the rolling direction between passes) modes. Microstructure, texture and mechanical properties were analysed. The observed differences in structure and mechanical properties were modest, and therefore further investigation of the effects of other kinds of asymmetry is suggested.

Abstract: Polycrystalline copper of 4N purity has been deformed by equal channel angular pressing at room temperature using route BC. Local textures have been measured by high-energy synchrotron radiation along 3 lines in the cross section from the top to the bottom of the billets. The texture heterogeneity observed in the cross section is presented for 2 passes and discussed with regard to friction-affected material flow.

Abstract: 3N nickel has been deformed by equal channel angular pressing (ECAP) at 400°C up to 3 passes using route A. The texture with respect to position in the deformed billet, i.e. from top to bottom, has been measured with high-energy synchrotron radiation. It is characterized by texture components typical for simple shear in the intersection plane of the square-shaped 90° bent channel. Besides, an oblique cube component is observed. Orientation imaging microscopy clearly shows that this component is due to partial recrystallization. Intensities of the texture components as well as deviations from their ideal shear positions vary from the top to the bottom of the billet and with the number of passes. The change of the intensity of texture components and the texture gradient investigated is discussed. Special emphasis is put on the influence of dynamic recrystallization on texture and microstructure formation during ECAP of fcc metals.

Abstract: A model describing the evolution of the misorientation angle between dislocation cells with plastic strain is proposed. The model is applied to the case of equal channel angular pressing (ECAP) of copper. In a basic version of the model, the evolution of the average misorientation angle is traced. A way of handling the evolution of the misorientation angle distribution function using a probabilistic description is also outlined.

Abstract: The technical aluminum alloy AA 5109 with a strong cube rolling texture has been deformed at room temperature by equal channel angular pressing (ECAP) using three passes of route A. Samples for ECAP have been cut parallel and at 45° with respect to the rolling direction yielding different starting textures. The local texture after ECAP has been investigated by highenergy synchrotron radiation. It is characterized by typical shear components of face-centred cubic (fcc) metals which deviate from their ideal positions. The texture with respect to intensity and deviation from ideal positions of the components depends on the distance from the top of the extruded billet and changes from pass to pass. It is also strongly influenced by the starting texture. The texture gradient has been discussed in the light of Tóth’s flow line model. The texture results have also been compared with those of other fcc metals with different stacking fault energy.

Abstract: The Swift effect, i.e. the length changes during torsion of solid bars with axial freedom of deformation is analysed theoretically for polycrystalline copper. In the simulations, the bar is divided into 5 tubes and in each tube the texture development is simulated with the help of the Taylor viscoplastic polycrystal model. The distribution of the hydrostatic stress is obtained from the equilibrium equation and the zero axial force requirement is satisfied with the help of an iterative scheme. The simulations reproduce faithfully the observed axial deformation and texture development. A second technique, based on the minimum plastic power is also applied to predict the length changes and textures. This technique leads to results which are nearly equivalent to the results obtained from the technique based on the equilibrium equation.

Abstract: Using a simple analytical flow function, an analysis of the deformation field in symmetrical rolling has been carried out. The so-obtained varying velocity gradient is incorporated into the Taylor polycrystal plasticity model to simulate the development of the deformation texture. The initial discontinuity in the deformation field of the entering material element on the flow lines is also taken into account. Multiple passes of the material is simulated. A strong texture gradient is obtained in good agreement with experiments carried out for rolling of plane carbon steel. It is shown that the shear component of the texture is strongly related to the nature of multiple passes of the rolling operation.

Abstract: FCC metals with different stacking fault energy (SFE), namely Al, Ag and Cu have been investigated for the evolution of crystallographic texture during ECAE deformation using Route A. Different materials with different SFE result in their characteristic textures. The results have been analysed on the basis of microstructural features and related established concepts on texture evolution in FCC metals.