Papers by Author: Jerzy A. Szpunar

Abstract: A model for intergranular damage propagation in polycrystalline materials is proposed, based on Markov Chain theory, Monte Carlo simulation and percolation concept. The model takes into account crack branching and coalescence, multiple crack nucleation sites, crack-turning etc., as well as the effect of grain boundary plane orientations with respect to the external stress direction. Both honeycomb and voronoi microstructures were utilized as the input microstructures. The effect of multiple crack nucleation sites has been found to have great influence on the crack propagation length. It has been observed that percolation threshold reported in the literature based on hexagonal microstructure is not applicable when the effect of external stress direction on the susceptibilities of grain boundaries is considered. The successful integration of voronoi algorithm with the Markov Chain and Monte Carlo simulations has opened up the possibilities of evaluating the intergranular crack propagation behaviour in a realistic manner.

Abstract: Controlling texture and microstructure evolution during annealing processes is very important for optimizing properties of steels. Theories used to explain annealing processes are complicated and always case dependent. An recently developed Monte Carlo simulation based model offers an effective tool for studying annealing process and can be used to verify the arbitrarily defined theories that govern such processes. The computer model takes Orientation Image Microscope (OIM) measurements as an input. The abundant information contained in OIM measurement allows the computer model to incorporate many structural characteristics of polycrystalline materials such as, texture, grain boundary character, grain shape and size, phase composition, chemical composition, stored elastic energy, and the residual stress. The outputs include various texture functions, grain boundary and grain size statistics that can be verified by experimental results. Graphical representation allows us to perform virtual experiments to monitor each step of the structural transformation. An example of applying this simulation to Si steel is given.

Abstract: Recrystallization texture in grain oriented silicon steel at different annealing temperature is investigated. Normalized x-ray intensities of various orientation components observed in Orientation Distribution Function are used for comparison. The computed CSL boundary distributions about Goss component with annealing condition were calculated. The misorientation angle distribution is also measured in order to find the importance of high-energy boundary with misorientation 20~45° range for the secondary recrystallization of Goss grain. From the analysis of CSL boundary distribution and misorienation angle distribution, the distribution of CSL boundaries does not evidently show any preferred difference between Goss and other texture components. Whereas, the misorientation angle analysis shows that the number of 20°~45° misoriented boundaries is higher around the Goss grains than around other texture components.

Abstract: The magnetic properties of nonoriented electrical steels are influenced by grain size and texture of final products. The key technology in the commercial production of nonoriented electrical steels is to grow grains with {hk0}<001> texture up to the optimum size in the final annealing process. The problems related to grain size control have been extensively investigated, while texture control has received much less attention. Therefore, there is enough room to improve the magnetic properties through the control of texture. In this study, systematic investigations on the texture evolution during both recrystallization and grain growth have been made. The formation of recrystallization texture is explained by oriented nucleation. This is supported by the fact that the area fraction of nuclei or recrystallized grains with specific orientation to all new grains remains almost constant during the progress of recrystallization. Most nuclei have a high misorientation angle of 25∼55° with the surrounding deformed matrices. During the progress of grain growth, the Goss texture component continues to decrease because the Goss grains have a high percentage of low angle, low mobility grain boundaries. The grains of Goss orientation have a smaller grain size than those of random orientation.

Abstract: In nonoriented electrical steels, the control of texture has received little attention, and hence there is an unexplored possibility to improve the magnetic properties of nonoriented steels through texture control. Furthermore, the formation of recrystallization texture in these steels has not yet been systematically studied. In this study, such systematic investigations are undertaken for nonoriented electrical steels with 2% Si. New information obtained from EBSD measurements on partially recrystallized specimens will allow us to know what is happening during the recrystallization stage. The formation of recrystallization texture is much better explained by oriented nucleation. This is supported by the fact that the area fraction of nuclei or recrystallized grains with specific orientations for all new grains remains almost constant during the progress of recrystallization. Most nuclei have a high misorientation relationship with the surrounding deformed matrix: 25~55
. The main texture components of nuclei or recrystallized grains during the progress of recrystallization are Goss and {111}<112>. Deformed {111}<110> and {111}<112> grains generally disappear at the early stage of recrystallization whereas deformed {001}<110> and {112}<110> grains are mostly consumed at the late stage of recrystallization.

Abstract: The oxide film, which is formed on the Zr-2.5% Nb pressure tube surface serves as a protective barrier against hydrogen ingress. Hydrogen ingress is a diffusion process and therefore is affected by the distributions of oxide orientation, grain size, shape, and boundary. Our previous research has focused on understanding the oxidation mechanism and predicting the hydrogen ingress and oxidation kinetics. In this paper, a simple model has been established to simulate the effects of cracks/voids on diffusion process. This model can be potentially used to study the influences of oxide cracks on hydrogen permeation. The effects of the volume fractions, orientation and distributions of cracks on the steady state diffusion flux are simulated.

Abstract: The quality of steel sheets is strongly affected by the surface defects that can be generated during hot rolling and are often related to scales removal operation. These defects are related to rather complex high temperature oxidation processes. In order to reduce an occurrence of the defects, it is necessary to understand better the formation of iron oxides during high temperature oxidation, the structure of the interfaces with the substrate and between different oxide phases. However, due to the lack of good experimental research tools details of iron oxide microstructures were not investigated. Conventional methods, such as backscattered electron images or fractography can only provide general characteristics of microstructures like grain morphology and grain size. In this paper the microstructure, phase distribution and texture in oxide formed during high temperature oxidation of iron and low carbon steels are investigated. The oxide microstructures are characterized by orientation imaging microscopy (OIM) on the cross-sectional area of the oxide layers. It is demonstrated that OIM using electron backscattered diffraction (EBSD) techniques, can be used to distinguish grains having different phase composition and orientation and can become invaluable tool for visualizing the oxide microstructure, texture and also can be used to study oxide defects. The three different iron oxides phases can be distinguished and the characteristics of oxides with different oxidation histories compared The characteristics of high temperature oxidation microstructure of iron are presented with description of iron oxide defects and cracking as well as the illustration of the interfacial microstructure between the layered iron oxides.

Abstract: Polycrystalline materials develop texture as a result of various manufacturing processes. In this paper the effect of texture of material on wear resistance and friction coefficient of AISI304 stainless steel samples was studied. Three different types of surface textures were produced from the same stainless steel raw material. Texture measurements were performed to obtain information from the specimen surface. Friction tests were performed using a Micro Scratch tester with the capability of monitoring acoustic emission and frictional force during scratch tests.

Abstract: The article takes into account various factors which effect the texture evolution in the Cu lines. We propose here an explanation for the formation of {111}<110> and {111}<112> texture in the Cu lines. The explicit role of principal stresses, shear stresses and dislocations is discussed. The influence of line spacing on strength of the {111}<110> and {111}<112> texture components is also demonstrated in relation to the dislocation density.

Abstract: In the present paper we report the texture and microstructure dependence of electromigration damage in Cu interconnects. This was made possible by ncorporating a sophisticated set of instrumentation within the SEM which enabled in-situ monitoring of the electromigration defects. The electron backscatter diffraction (EBSD) maps were obtained before and after the completion of the electromigration tests. Thus, by comparing the maps before and after the failure it was possible to associate the texture and microstructure with both failure sites - voids and hillocks. Results from lines down to 130 nm are included and orientation dependence of the defects is discussed.