Papers by Author: Werner Skrotzki

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: Up to now most of the research on Ni-Mn-Ga alloys was concentrated on single crystals. However, there is a great interest in polycrystals for technical applications. Recently, polycrystalline Ni50Mn29Ga21 rods of 25 mm diameter and 400 mm length were prepared by hot extrusion. The <100> <110> double fibre texture of the extruded rods was measured with high-energy synchrotron radiation. The microstructure after hot extrusion was analyzed with electron backscatter diffraction. Within the recrystallized grains all three martensitic variants have developed during cooling. Variants with twin boundaries preferentially aligned along the extrusion direction predominate.

Abstract: The development of the volume fraction of cumulated persistent slip bands (PSBs) in cyclically deformed nickel polycrystals was investigated in dependence on the number of cycles using scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was shown that there is a large scatter of the volume fraction of PSBs from grain to grain. Three different tendencies for the development of the volume fraction with increasing number of cycles were distinguished. It was shown that there is a correlation of the orientation of the primary slip systems with the volume fraction of cumulated PSBs and the activation of PSBs during half-cycle deformation.

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: 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: Epitaxial thin films of the superconducting borocarbide compound YNi2B2C were grown on single crystal MgO (100) substrates without and with Y2O3 buffer layer using pulsed laser deposition (PLD). In both cases YNi2B2C grows with [001] normal to the substrate. However, the in-plane texture depends on the starting condition. For samples without buffer layer, oxygen from the substrate diffuses into the film and forms an Y2O3 reaction layer at the interface. As a consequence, a deficiency of Y is generated giving rise to the formation of secondary phases. On the other hand, using an artificial Y2O3 buffer layer secondary phases are suppressed. The texture of the Y2O3 layers determines the texture of the YNi2B2C film. The superconducting properties of the borocarbide films are discussed with respect to texture and phase purity.

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.

Abstract: Texture and microstructure were investigated after 1 pass equal channel angular extrusion (ECAE) of a single crystal cube oriented Ni billet. Neutron and X-ray diffraction were used to determine global and local textures, respectively. EBSD and TEM investigations were also carried out in order to study fine scale microstructural features. Substantial variations in texture and microstructure, resulting from different efficiencies in the shearing process, were locally recorded through the billet height. The deformation was heterogeneous on both micro and macro scales.

Abstract: Silver of 3N purity was deformed at room temperature by equal channel angular pressing (ECAP) using three passes of route A. The global and local texture were investigated by neutron diffraction and high-energy synchrotron radiation, respectively. The texture is characterized by typical simple shear components of fcc metals which differently deviate from their ideal positions. Local texture measurements reveal that the intensity and inclination of the texture components with respect to the extrusion direction depend on the distance from the top of the extruded bar and change from pass to pass. Reasons for the texture gradient are discussed. The texture of silver is compared with that of copper having a higher stacking fault energy.

Abstract: Polycrystalline samples of NiAl have been deformed in torsion in the temperature range 800K – 1300K. Deformation is accompanied by dynamic recrystallization, which with increasing temperature changes from continuous to discontinuous mode. Emphasis was put on the occurrence of continuous dynamic recrystallization, which will be discussed with respect to texture and microstructure.