Papers by Author: Jan T. Bonarski

Abstract: The common feature of the technologies, such as the equal channel angular pressing (ECAP) is the use of a changeable deformation path, which changes the configuration (value and direction) of the acting forces that impose various directions of plastic flow. The changes destabilize a temporary dislocation structure as well as the spatial distribution of the areas with elevated elastic energy cumulated in deformed lattice. The application of that technique results in a potentially large deformation (up to several hundred percent) and plasticity of materials considered to be brittle at ambient temperature. The microstructure effects accompanied with intensive and large deformation are reflected in the space orientation of grains (crystallographic texture) as well as in the configuration of the residual stresses existing in deformed material. The presented results based on experimental data registered by X-ray diffraction and TEM techniques are helpful in interpreting deformation mechanisms operating in the bend-zone of the ECAP tool during processing Ti-ingot by the mentioned method of severe plastic deformation.

Abstract: The effects associated with the change of the deformation path - such as the replacement of homogeneous multi-slip by heterogeneous deformation and a decrease of global strain hardening - have been utilised in the metal forming operation termed KOBO technology. In the case of extrusion it consists in reversible, cyclic twisting of a billet under the extrusion force. The technology enables extrusion of metals with very large deformation in one operation at low temperature. A complex scheme of straining, large cumulated deformation and low temperature of the process results in a fine grained microstructure of the extruded material (product). The new technology requires detailed studies of the mechanism of the plastic deformation with the specific geometry of the zone of metal flow during extrusion. Essential in these studies is the information on the texture and microstructure in the deformation zone. The aim of this work is therefore to disclose the deformation mechanisms on the basis of the observations of microstructure and texture evolution in the zone of plastic flow of the extrudate. Coarse grained polycrystalline billets of magnesium alloys AZ31 were extruded by KOBO at room temperature and also by a conventional method at about 400°C. Methods of texture topography as well as optical observations reveal the specific microstructure and texture in mezzo and micro scale of heavily deformed material after extrusion. It is worth mentioning that the KOBO process leads to compact and rather homogeneous extrudates even in the case of AZ alloys. These hexagonal metals cannot be cold-formed to a high reduction with conventional techniques.

Abstract: Relatively high mechanical strength and simultaneously good plasticity of a crystalline material are determined by the state of its internal structure, preferably nano- or ultra-fine grained one. To achieve the above combination of properties, various manners of plastic deformation and heat treatment are applied in practice. One of the most effective processes in this field is severely plastic deformation, e.g. by the method of equal angular channel pressing (ECAP). During the ECAP, favourable effects of grain fragmentation and the formation of specific orientation relations can be attenuated by the process of structure recovery, especially, when the real temperature of angular extrusion is elevated for physical or technological reasons. An attempt to modify the ECAP technology was considered, to avoid the unfavourable temperature effects and to increase at the same time the efficiency of manufacturing the ultra-fine structure of material. Extrusion of dual-material (AZ31 + Al) ingot was performed at room temperature. As it seems, the well known difficulties with plastic deformation of materials with hexagonal lattice symmetry, like AZ31 alloy, have been decreased. Both experimental and methodological aspects of the angular extrusion of the dual-material ingot and chosen microstructure characteristics (texture, stress, morphology) are presented. On the basis of the suggested modification, the text discusses an explanation of physical origins of the microstructure evolution in the investigated material revealed by experiments.

Abstract: In the paper some aspects of analysis of crystallographic texture concerned to evaluation^of its inhomogeneity have been described. The introduced classification and quantitative measure of texture inhomogeneity have been applied in microstructure characterization of cold rolled Cu-sheet and of electrodeposited Cu-layer with a depth-graded structure.

Abstract: Crystallographic texture is one of frequently investigated properties of near-surface regions. From the application point of view, the inheritance effect of the crystallographic orientation of a substrate is important for layered structures. The investigation of the texture of layered structures or gradient materials by means of X-ray diffraction back-reflection pole figure measurements requires a control of the information depth. Such measurements at a controlled information depth can be achieved by means of non-symmetrical diffraction geometry, employing a constant value of falling angle of the incident beam. Thus, the texture of near-surface layers with a defined thickness can be examined, as in tomographic techniques. In this work, the method of texture analysis based on a controlled information depth was applied to the investigation of the texture inheritance of a Zn protective layer on deep drawing steel. Moreover, the crystallographic relations between the texture of substrate and deposited layer, termed as texture inheritance, were considered.

Abstract: The traditionally applied registration method of the back-reflection pole figure is based on the equiangular measurement lattice. It determines also the equiangular character of presentation of measurement results in form of stereographic projection, termed as the pole figure. The mentioned registration mode is characterized by an unequal density of the measurement points on the pole figure. It is the evident disadvantage of the traditional registration mode. In order to eliminate the drawback, and to increase the efficiency of the measurement procedure, an optimization of the registration method was made. The optimization consists in dividing a reference sphere of the stereographical projection into uniform regions, so called equal solid angles (ESA). As a result of the applied optimization, over 40% reduction in number of the measurement points and in the registration time at preserved pole figure quality was obtained. For verification of the new solution, a set of experimental pole figures of cold rolled copper by the traditional mode as well as the introduced ESA one was recorded. Comparison of the results of texture analysis based on the orientation distribution function was carried out. The results of measurements performed by the ESA method confirm the efficiency of the introduced optimization.