Papers by Author: Jacek Tarasiuk

Abstract: In the paper authors presented the application of specific method of assessment chosen properties of coating layer, that give additional information strictly connected with its tribology properties. Nanotomography techniques and 3D image processing gives quantitative and qualitative information about the testing sample, with no negative effects on the exanimating layer. Two samples, one with and one without the laser treatment were tested, measured and obtained results presented and discussed. Those preliminary research shown that proposed method can be recommended to application as a supplementary test of the properties coating layers and for verification of technological process parameters on the stage of working out the production process.

Abstract: EBSD investigation of texture and microstructure evolution during a complete thermomechanical treatment of commercially pure titanium (HCP-Ti) is presented. Titanium was cold rolled to reach various degrees of thickness reduction: 20%, 40% and 60%. Next, annealing in air atmosphere was conducted at different conditions to achieve the recrystallized state. EBSD topological maps were measured on RD-TD and RD-ND surface of each sample. Strong heterogeneity of deformed titanium microstructures is described with focus on the important role of twinning mechanisms. Texture evolution in investigated titanium appears to be limited, especially in recrystallized state. However some subtle mechanisms are discussed.

Abstract: EBSD (Electron Backscatter Diffraction) is a modern experimental technique which allows to represent the information about texture and microstructure in the form of a topological map comprised of a very large number of acquisitioned orientation points. Such a map can be easily used to analyze grain boundaries. In TSL OIM Data Analysis software it is mainly done by Line Segments Method, in which grain boundaries are represented as lines separating pairs of EBSD points for which the misorientation value is within a specified range. The aim of this work is to present a complementary method of grain boundary characterization. In this case, a GB consists of specially selected EBSD points and is thus represented as a two dimensional area. As a result, new possibilities of GB analysis emerge, such as texture of GB areas. The provided description may be also more compatible with a real microstructure, especially after deformation, in which grain boundaries (especially the one with small misorientation) are indeed areas of lattice defects accumulation.

Abstract: The analysis of deformed and recrystallized zirconium, used in nuclear industry is presented. The main purpose of the present work is to describe and analyze changes in texture, microstructure and misorientation profile, which are observed during a complete thermomechanical treatment. Zirconium samples were channel compressed till various degrees of deformation. The samples were then annealed. In both deformed and recrystallized states, topological maps were measured using the well known EBSD (Electron Backscatter Diffraction) technique. The obtained data were necessary for further analysis which consisted of several approaches: quantification of textures, identification of principal components, volume fractions, misorientations, grain size and IQ histograms. For the misorientation analysis, several parameters have also been tested (ie. correlated misorientation profile, grain average misorientation, kernel, etc.). Based on this complete set of data a scenario is proposed to explain the observed microstructural evolutions.

Abstract: Eight years ago recrystallization of OFE (oxygen-free electronic) copper was examined in detail using various techniques. In 2008 exactly the same material was measured using EBSD microscopy. The deformed state and fully recrystallized state have been analyzed and compared with data obtained eight years ago. The stored energy (SE) estimated by Image Quality (IQ) analysis was compared in these two cases. A significant amount of recovery took place in the sample, but only in some texture components. Some others present more or less the same SE as eight years ago. The textures of recrystallized samples were compared. We observed that the difference in SE distribution between the two deformed state has an influence on the final textures after recrystallization. Our study confirms the hypothesis that if a grain (orientation) has distinctly lower SE than other orientations - it has the highest growth preference (threshold hypothesis). Such grains (orientations) are dominant in the recrystallization texture.

Abstract: The genetic algorithm method was used in the present work as an alternative to classical calculation methods. It can be used in the situations where we search an optimal solution and a problem has many variable parameters. In this work the genetic algorithm method was applied in order to decompose the texture function into ideal components and also to optimize elastic constants by an appropriate choice of texture function. These example applications of genetic algorithm method show its potential in the field of material engineering.

Abstract: The stored energy distribution versus crystal orientation in polycrystalline copper was determined using synchrotron radiation. This distribution is an important input data for recrystallization models. The stochastic vertex model of recrystallization was used in the present work. It is a mixture of the classical vertex model and the Monte Carlo algorithm. Both grain boundary energy and stored energy are taken into account in the calculations. In each elementary step, a reasonably small, random modification of a given vertex position is generated and a corresponding total energy change of a system is calculated. A new vertex position is retained with a probability proportional to the Boltzmann factor. In such a way one avoids solving a complex system of equations. This approach is also closer to the stochastic nature of recrystallization process. The inclusion of the stored energy distribution in the above model enables a good explanation of the recrystallization process. The recrystallization textures for polycrystalline copper rolled to low and high reductions were predicted in agreement with experimental results.

Abstract: Stored energy is generally considered as a main driving force of recrystallization process. After plastic deformation a high dislocation density and residual stress field remain in a material. Both quantities are at the origin of the stored energy and we call them as the “plastic” and “elastic” parts of this energy. Their orientation distributions can be determined using diffraction and deformation models. Both components of the stored energy are studied in the present work. Their distributions and characteristics are studied for f.c.c. and b.c.c. materials.

Abstract: Plastic deformation induces the dislocation and residual stress fields, which rest in a material after releasing of applied external forces. One can distinguish the stored energy connected with dislocation density and that with residual stresses. The stored energy distributions can be determined experimentally by diffraction experiments and also can be predicted by deformation models. The so obtained distributions of the stored energy versus crystal orientation were correlated with deformation and recrystallization textures of low carbon steel.

Abstract: Classical vertex model till now described only the grain growth stage and not the primary recrystallization. In the present work the vertex model is first extended in order to take into account the both stages of recrystallization process. The influence of the stored energy is taken into account and some phenomenological laws describing the evolution of grain boundary energy and mobility with misorientation angle are used. Nucleation is considered to be site-saturated. The experimentally determined stored energy values, crystallographic orientations and boundary misorientation distributions are used in order to characterize the initial microstructure. The model is tested to study the recrystallization of 70% and 90% cold rolled polycrystalline copper during an annealing treatment. In order to explain the texture evolution in both cases, it is necessary to introduce an energy threshold for grain boundary movement, i.e. a minimal value of the stored energy difference between a nucleus and the deformed material necessary to provoke grain boundary motion. The developed model is shown to predict texture evolutions in good agreement with experimental data.