Papers by Author: Henryk Paul

Abstract: In this study, the commercial purity Al/Cu plates were bonded through the explosive welding process. The SEM/EBSD local orientation measurements were conducted to consider the changes in the microstructure and the development of texture gradients for the applied explosive loading. A particular attention was paid to the texture changes across the interface. The detailed local orientation measurements show that the ultra-fine grained layers are formed close to the bonding zone. The layers were characterized by the copper-type rolling texture components. The interface was outlined by a characteristic sharp transition between the two materials. However, in some places, local melted zones were also encountered, mainly in the front slope of the waves.

Abstract: This paper describes nucleation and grain coarsening at very early stages of recrystallization in AA3104 aluminum alloy containing complex structure of second phase particles. Measurements of individual sub-cell orientations in ECAP-processed and slightly annealed structures were possible by using TEM-based orientation mapping in combination with recrystallization carried out in the microscope. The results were compared with those obtained by SEM/EBSD system. The investigation shows that the 40^o<111>-type relation occurs rarely, and the rotation axes of misorientations between deformed and recrystallized areas were strongly scattered. Grouping of the misorientation axes near the <012>, <221>, <112> and <110> crystallographic directions was noticeable.

Abstract: The objective of the study was to determine the effect of strain path on texture, microstructure and mechanical properties development of severely deformed Al-Mn-Mg alloy. The commercial purity material (AA3104 alloy) was deformed via Equal Channel Angular Pressing (ECAP) up to 10 passes following routes A, B, and C. The deformed and partially recrystallized microstructures and the crystallographic textures were characterized by transmission (TEM) and scanning (SEM) electron microscopy including systematic local orientation measurements (TEM and SEM FEG orientation mapping). The crystallographic texture was determined using X-ray diffraction on a sample section perpendicular to the extension direction (ED). In order to estimate the homogeneity of strengthening the systematic measurements of Vickers micro hardness in the plane perpendicular to the ED was performed. It was found out that different routes led to strong differences in microstructure of billets. In the case of route A and B strong macro cracking appeared after 5 and 3 passes, respectively. A good quality billet after 10 passes was obtained only in the case of route C. Texture evolution turned out to follow nearly the same ‘course’ for different routes of ECAP. However, the intensity of particular texture components was different in each case. TEM observations and local orientation measurements allowed identifying fine and strongly disoriented planar dislocation structure of nanolayers in the case of route A and C. In the case of route B nearly equiaxed structure of fine grains was observed after 3 passes. Moreover, irrespective of the applied deformation routes large, not deformable second phase particles strongly influenced strengthening of the matrix and nucleation during the recrystallization.

Abstract: Periodic crystal lattice rotations within compact clusters of shear bands, developed in copper, have been characterized over a range of scales by optical microscopy, high resolution FEG-SEM-EBSD and TEM orientation mapping, to examine the role of local lattice re-orientation on slip propagation across pre-existing barriers to dislocation motion. Two different cases were analysed in detail. The single crystal analysis addresses the relation between the crystallographic microtexture and microstructure development due to the crystal anisotropy after a strain path change. All the changes in strain path directly lead to crystallite subdivisions and strain localization in the form of macroscopically visible bands of different morphology at the micro scale. The elongated cell substructure formed during primary straining was the source of anisotropy after changing deformation path. It is thought that the presence of this structure (here subcells) as barriers to dislocation motion is crucial for the occurrence of shear banding. The analysis of pure polycrystalline copper has been focused on the influence of local lattice re-orientations within particular grains on slip propagation across grain boundaries. The crystal lattice rotated in such a way that one of the {111} slip planes became nearly parallel to the direction of maximum shear (due to the actual state of anisotropy). A natural consequence of this rotation was the formation of a specific microtexture which facilitated slip propagation across grain boundaries.

Abstract: The development of the new technology for manufacturing of multi layer aluminium based materials for heat radiators is the subject of this work. Modern aluminium alloys can be specially processed in a controlled manner to obtain nano(mikro) structures. These ultra fine grained structures play a significant role because they provide a possibility to obtain final product that is characterized by elevated strength properties and, at the same time, good anticorrosion and soldering properties. A detailed understanding of these ultra fined structures using a combination of numerical modelling and experimental analysis is presented in this paper. Particular attention is put on implementation of the microstructure evolution model into the finite element software to simulate Equal Channel Angular Pressing (ECAP) process. Examples of the obtained results are presented and discussed.

Abstract: The relations between the active slip systems within the deformed state and the orientations of the first formed nuclei of recrystallized grains have been studied in strongly deformed samples of high purity aluminium single crystal and polycrystalline aggregates. The new grain orientations and misorientations were followed by systematic local orientation measurements using SEM-FEG/EBSD and semi-automatic measurements in TEM. Investigations of the direction of growth indicate the privileged role of {111} planes in the initial stages of recrystallization. The grain boundary migration and ‘consumption’ of the as-deformed areas was always favoured along directions parallel to the traces of the most active {111} slip planes as shown clearly in the stable and structurally homogeneous Goss{110}<001> oriented crystallite. In the case of polycrystalline material the influence of grain boundaries and their triple junctions on the crystallographic aspects of nucleation is discussed.

Abstract: The nucleation of new grains during annealing in high purity single crystals of Cu-8%wt. Al alloy with initial (112)[111] orientation has been characterized by detailed transmission electron microscopy (TEM) orientation measurements. The samples were channel-die deformed and then recrystallized to form a substructure composed of a mixture of deformation twins, shear bands (SBs) and the recrystallized grains. Substantial progress in understanding the mechanism of texture transformations at the early stages of recrystallization was possible thanks to orientation mapping using TEM. Microtexture analysis of partly recrystallized samples indicates a simple 25-40o (<111> or <112>) relation, most frequently observed during the early stages of recrystallization between single nuclei and one of the two as-deformed groups of components (twins or matrix). As recrystallization proceeds, recrystallization twinning develops strongly and facilitates rapid growth of the recrystallized phase. The first and higher generations of twins systematically tend to obscure the initial crystallographic relation between the deformed state and the recrystallization nuclei.

Abstract: Microstructure and texture development in twinned fcc metals is investigated in order to characterize the influence of micro- and macro-scale brass-type shear bands (SB) on structural and textural changes at large deformations. TEM and SEM analyses are focused on bands developed by plane strain compression in twinned C{112}<111> oriented single crystals. The proposed crystallographic model of the shear banding phenomenon refers to the idea of local lattice reorientation within narrow areas. Most of these rotations occur around the TD||<110> axis with significant further rotations about <112> poles. These two rotations explain the influence of SB’s on the formation of Goss{110}<001> and brass{110}<112>-S{123}<634> texture components clearly observed in highly deformed low SFE metals. At high deformations symmetrically equivalent crystal lattice rotations inside narrow areas lead to the formation of positive and negative macroscopic SBs.

Abstract: The crystallography of recrystallization nucleation has been investigated in channel-die deformed pure aluminium bicrystals with {100}<011>/{110}<001> and {100}<001>/{110}<001> orientations. The new grain orientations and misorientations were followed by systematic local orientation measurements using SEM and semi-automatic measurements in a TEM. In particular, orientation mapping combined with in-situ sample heating was used to investigate the formation and growth of new grains and their crystallographic orientation changes at very early stages of recrystallization. Grain boundary migration and ‘consumption’ of the as-deformed areas was always favoured along directions parallel to the traces of the {111} slip planes that had been most active during deformation. The orientations of the first formed nuclei were misoriented with respect to the orientations identified within the neighbouring deformed areas by α(<111>, <112>, or <100>)relations.

Abstract: The local crystallography within shear bands (SB) has been examined in a single crystal of {112}<111> orientation of pure copper deformed at 77K by channel-die compression to strains of about 1. Setting up a system for making high-resolution orientation maps using transmission electron microscopy (TEM) has opened new advantageous circumstances for the analysis of orientation changes within SB. This method with spatial resolution higher than 10nm allows the examination of microstructure images composed of nanoscale subcells forming SB. It has been found that for well-developed shear bands, a crystal lattice rotation about <112> direction tends to dominate and this process is usually accompanied by activation of new slip systems. The present work shows that despite the plane strain deformation mode, the mechanism of lattice rotation within emerging SBs may lead to Goss and Brass texture components.