Papers by Keyword: Crystallographic Texture

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Authors: Vincent Klosek, Marie Helene Mathon, M.H. Aouni, Rémi Chiron, Vincent Ji
Abstract: By associating texture determinations and strains measurements by neutron diffraction, the elastoplastic behaviours of families of crystallites with the same crystallographic orientations were characterized in situ in a brass and a bronze alloys under uniaxial loading. The polycrystalline orientation analysis method proposed here allows an intermediate approach between a “local” (intragranular) and a “global” characterization, within the bulk of massive samples.
Authors: Jan T. Bonarski, Jan Pospiech, Leszek Tarkowski, Jan Kuśnierz
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.
Authors: Hari K. Duvvuru, Marko Knezevic, Raja K. Mishra, Surya R. Kalidindi
Abstract: Microstructure Sensitive Design (MSD) offers a rigorous mathematical framework for representing the relevant statistical details of the material microstructure for a given design problem, and for developing quantitative invertible relationships between these microstructure representations and the macroscale properties of interest. The methodology makes extensive use of Fourier representations of the distribution functions representing the material internal structure and existing homogenization theories. In this paper, we describe the application of the MSD framework to fcc polycrystals with a specific focus on the crystallographic texture as the microstructure design variable. The advantages of the MSD approach are demonstrated through a number of elastic-plastic property closures for cubic metals.
Authors: Jean Savoie, Melinda Bissinger
Abstract: Aircraft engine components are assemblies of several parts that are manufactured using various processes: deep drawing and machining, among others. Deep drawing cannot control accurately wall thicknesses and is performed in numerous steps. Machining parts from solids is less and less cost effective as prices for raw materials increase. Hence, the use of near net shape manufacturing methods is becoming more appealing. An alternative forming process is here investigated: flowforming, process well adapted to axisymmetric parts. The amount of forming steps, welding and machining could be significantly reduced, reducing lead-times and manufacturing costs. Examples are presented for the forming of selected parts (gas generator cases, fan cases and diverter ducts), together with their metallurgical and mechanical properties. Flowforming, however, can only generate shells with some hollow details: most flanges, bosses, stiffeners or weld lips cannot be obtained. Hence, methods of adding material are explored.
Authors: F. Bai, P. Cizek, Eric J. Palmiere, Mark W. Rainforth
Abstract: The development of physically-based models of microstructural evolution during hot deformation of metallic materials requires knowledge of the grain/subgrain structure and crystallographic texture characteristics over a range of processing conditions. A Fe-30wt%Ni based alloy, retaining a stable austenitic structure at room temperature, was used for modelling the development of austenite microstructure during hot deformation of conventional carbon-manganese steels. A series of plane strain compression tests was carried out at a temperature of 950 °C and strain rates of 10 s-1 and 0.1 s-1 to several strain levels. Evolution of the grain/subgrain structure and crystallographic texture was characterised in detail using quantitative light microscopy and highresolution electron backscatter diffraction. Crystallographic texture characteristics were determined separately for the observed deformed and recrystallised grains. The subgrain geometry and dimensions together with the misorientation vectors across sub-boundaries were quantified in detail across large sample areas and the orientation dependence of these characteristics was determined. Formation mechanisms of the recrystallised grains were established in relation to the deformation microstructure.
Authors: Kunio Ito
Abstract: The migration rates of C->Si, Si->C, and Si->Sj were assumed to be high and those of Si->Si and all other rates to be low. Here Si(i=1,2,3,4) is a variant of S orientation and C->Si means the growth of a cube grain into an Si grain. The textural development through grain coarsening was simulated as a function of the ratio of the high rate to the low one. The compromising effect surely promotes the development of the cube texture but its decisive development requires any asymmetry between C->Si and Si->C migration processes.
Authors: Laurent Delannay, Oleg V. Mishin
Abstract: Textures of rolled sheets are typically orthotropic along the mid-thickness plane, where the material undergoes plane strain compression. At the surface and in the subsurface layers, however, the achievement of the orthotropic symmetry can be impeded due to friction between the sheet and the rolls. The through-thickness strain distribution and texture have been found to also depend on the rolling draught [1], the load exerted on the rolls, the temperature and the rolling speed. Valid predictions of the influence of the shear deformation on the development of the microstructure and texture are not only important for controlling structural characteristics of the as-deformed material, but are also a pre-requisite to the investigation of the recrystallization process upon annealing. A recent experimental study of the texture development in heavily rolled aluminum revealed that the texture in each subsurface layer was dominated by one of the symmetric variants of the “copper” component. To investigate the conditions under which such variant selection is expected, a crystal plasticity theory combined with several mean-field as well as full-field scale-transition schemes is applied in the present work. Model predictions are compared to the texture development measured by EBSD in samples rolled to high and ultrahigh strains.
Authors: Igor V. Alexandrov, Vil D. Sitdikov
Abstract: In this article we present the results of the experimental research and those of the processes developing the crystallographic texture of computer modeling in CP Ti in the process of 1-4 equal channel angular pressing (ECAP) passes along the route ВС. The goal of the research was to determine the active deformation mechanisms, depending on the strain degree, accumulated in the ECAP process. The research was carried out by the method of X-ray analysis and by computer modeling. Computer modeling was carried out on the example of visco-plastic self-consistent model. Thereby, the basal, the prismatic and the pyramidal (of the 1st and of the 2nd order) slip systems were considered as possible active slip systems. Besides, the possibility of activating the tensile and the compressive twinning systems were taken into consideration. As the result of the carried out experimental research, the objective laws of forming preferred orientations were determined. For the first time, with the help of computer modeling, made up to the 4th ECAP pass, it was shown that the crystallographic texture development processes in CP Ti in ECAP, realized at temperature of 723 K, can be explained by activation of the basal, prismatic and pyramidal (of the 1st order) slip systems and compressive twinning systems. Therefore, the increase of the ECAP passes can lead to amplification of contribution of the basal and prismatic slip systems, as well as the insignificant weakening of the contribution of pyramidal slip systems (of the 1st order). Moreover, the compressive twinning can become obvious only in the 1st ECAP pass.
Authors: Ming Lin Jin, Cun Fu Zhu, Zhan Yong Wang, Qi Zhong Chen, Ke Jia Liu
Abstract: The Sr0.75La0.25Fe11.75-xCo0.25ZnxO19 hexaferrites are prepared by the ceramic process. Influences of the substitution of Zn2+ ions on crystallographic texture have systematically been investigated by pole figure analysis. The (008) and (107) pole figure shows that the pole intensities are axisymmetric at the center of c axis. With the increase of x, the lattice parameters a and c increase gradually till x=0.15. Excessive Zn2+ addition induces the much coarse grain. The easy-axis alignment of grains decreases from 77.5% to 75.5% for the substitution of Zn2+ ions from 0 to 0.25. When Zn2+ content was from 0 to 0.25, the magnetic properties of Br and (BH)max were increased, while Hcb and Hcj were decreased till x>0.2.
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