Textures of Materials - ICOTOM 14

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Authors: Stefan Zaefferer
Abstract: Orientation microscopy in TEM and SEM is a particularly well suited tool to study recrystallisation processes because these are always associated with orientation and microstructure changes. The present work discusses the possibilities and limits of the TEM and SEM based techniques and illustrates their use by means of 3 different examples. The examples include studies on nucleation mechanisms of primary recrystallisation where the techniques meet their limits in spatial resolution. The problem of in-situ observations of annealing processes is discussed and it is shown how recrystallisation simulation techniques based on experimental data may be used. Furthermore the new technique of 3-dimensional EBSD in a focused-ion-beam (FIB) SEM is presented with one example. Finally, the statistical analysis of very large orientation data sets is discussed by an example of secondary recrystallisation in electrical steels.
Authors: Thomas S. Key, Jacob L. Jones, William F. Shelley, Ben J. Iverson, Hsin Yu Li, Elliott B. Slamovich, Alexander H. King, Keith J. Bowman
Abstract: The anisotropy that is inherent to piezoelectricity is directly tied to the symmetry of domains within the crystals of polycrystalline piezoelectrics. Alloy design for these oxide materials is often focused on influencing pinning of domain walls in polycrystals that have been subjected to high fields and elevated temperatures to introduce the ‘poled’ condition from which most piezoelectric devices operate. We have investigated a wide range of these oxides consisting of single phases or mixtures of phases that may be all or partially piezoelectric in character. Crystal symmetries investigated include tetragonal, orthorhombic, rhombohedral and monoclinic with some phase transitions evolving during high-temperature processing or during poling. Materials investigated include a range of bismuth titanates, lead titanates, lead zirconate titanates and sodium niobates. A variety of texture evaluation techniques, including area detector x-ray diffraction, synchrotron x-ray sources, and neutron sources have been utilized along with Rietveld diffraction modeling tools to enable a deeper understanding of domain textures, domain texture evolution and synergistic relations between crystallographic textures and domain textures. This paper documents an understanding of texture and anisotropy in these materials, and provides insight on approaches to optimize textures for high performance in these materials and demonstrates how these tools can be used to evaluate processing variations from production of these materials.
Authors: Surya R. Kalidindi, J. Houskamp, G. Proust, H. Duvvuru
Abstract: A mathematical framework called Microstructure Sensitive Design (MSD) has been developed recently to solve inverse problems of materials design, where the goal is to identify the class of microstructures that are predicted to satisfy a set of designer specified objectives and constraints [1]. This paper demonstrates the application of the MSD framework to a specific case study involving mechanical design. Processing solutions to obtain one of the elements of the desired class of textures are also explored within the same framework.
Authors: Paul van Houtte, Albert Van Bael, Marc Seefeldt, Laurent Delannay
Abstract: The paper focuses on the multi-level character of existing or currently developed models for polycrystal deformation. A general multilevel frame is presented, which can be applied to models for the simulation of plastic anisotropy to be implemented in FE codes for the simulation of metal forming processes, or to models for the simulation of deformation textures. A short overview is presented of two-level models ranging from the full-constraints Taylor model to the crystalplasticity finite element models, including the description of a few recent and efficient models (GIA and ALAMEL). Validation efforts based on experimental cold rolling textures obtained for steel and aluminium alloys are discussed. Finally a recent three-level model which also takes the microscopic level (dislocation substructure) is discussed.
Authors: Timothy N. Debacker, Philippe Robion, Manuel Sintubin
Abstract: The anisotropy of magnetic susceptibility (AMS) is often interpreted in terms of strain. However, since AMS is controlled by all magnetic (s.l.) carriers present, an AMS interpretation is not straightforward, especially in the presence of composite magnetic fabrics. Considering the large number of factors that may influence rock mineralogy (e.g. sediment source area, metamorphism), it becomes clear that one cannot interpret AMS in terms of strain without applying additional techniques that allow determining the nature and preferred orientation of all magnetic (s.l.) carriers likely influencing the measured AMS. This is discussed using samples from the Brabant Massif (Belgium) and the Moesian Platform (E-Romania).
Authors: Leonardo Lagoeiro, Paola Ferreira, Cristiane Castro
Abstract: In this study we analysed microstructures and determined [c]-axis textures of quartz crystals in veins formed parallel to composition banding in naturally deformed iron oxide-quartz rocks. Only veins of few millimeters thick were sampled. These veins were formed in a regime of non-coaxial deformation under temperature of ~300°C. We made thin sections from rock slabs cut perpendicular to shear plane and parallel to shear direction. In thin sections veins are composed of large single quartz crystals of lens or rhomb-shaped blocks similar to s-porphyroclast systems. Lattice distortion (i.e. undulose extinction, gradual lattice banding and subgrain boundaries) occurs in single crystals as revealed by optical microscopy. Distortion was caused by slip of dislocations preferentially on basal planes. These are also planes along which microcracks developed. Distinct types of microcracks are individualized based on size, orientation and distribution of voids. Microcracrack voids are filled by polycrystalline quartz aggregates. In contrast to single crystals, these aggregates do not have any optical microstructure that might be related to crystal plastic process. Moreover grain size distribution are quite different from those related to dynamic recrystallized aggregates. Despite of that, polycrystalline quartz aggregates have strong [c]-axis preferred orientations. These orientations are similar to those of single crystals close to the microfracture walls. In large spaced voids c-axes orientation of quartz in polycrystalline aggregate have significant misorientation angles with respect to the single crystal [c]-axis orientation, reaching values up to 45° to the foliation plane (XY section of the finite strain). Based on microstructural and textural data we propose a mode for quartz [c]-axis texture development in both single crystals and polycrystalline aggregates that fill microcrack voids.
Authors: F. Heidelbach, B. Holtzman, S. Hier-Majumder, D. Kohlstedt
Abstract: The texture development in experimentally sheared aggregates of olivine was monitored as a function of increased water content and added melt. In dry samples, an alignment of {010} with the shear plane and <100> and <001> with the shear direction, respectively, was observed, consistent with intracrystalline glide on the (010)[100] and (010)[001] slip systems. Samples with high water content showed consistently stronger textures of the (010)[100] component for comparable shear strains indicating that water may especially ease glide on this slip system. Samples with added melt showed an increased alignment of {010} and <001> subparallel to shear plane and shear direction respectively, whereby the maxima were consistently rotated 10 to 20° against the sense of shear. This type of texture can be explained by a combination of increased glide on the (010)[001] slip system in combination with a partitioning of the strain between melt rich bands and relatively melt free regions in the sample. Physical anisotropies calculated from the textures indicate that increased water content causes enhanced anisotropy for longitudinal and transverse seismic waves. The addition of melt on the other hand may change the type of anisotropy that develops during deformation, but does not significantly change the magnitude of anisotropy compared to samples of pure olivine.
Authors: X.B. Wang
Abstract: Peak strength, mechanical behavior, and shear band (SB) of anisotropic jointed rock (JR) were modeled by Fast Lagrangian Analysis of Continua (FLAC). The failure criterion of rock was a composite Mohr-Coulomb criterion with tension cut-off and the post-peak constitutive relation was linear strain-softening. An inclined joint was treated as square elements of ideal plastic material beyond the peak strength. A FISH function was written to find automatically elements in the joint. For the lower or higher joint inclination (JI), the higher peak strength and more apparent strain-softening behavior are observed; the failure of JR is due to the slip along the joint and the new generated SBs initiated at joint’s two ends. For the lower JI, the slope of softening branch of stress-strain curve is not concerned with JI since the new and longer SBs’s inclination is not dependent on JI, as can be qualitatively explained by previous analytical solution of post-peak slope of stress-strain curve for rock specimen subjected to shear failure in uniaxial compression based on gradient-dependent plasticity. For the higher JI, the post-peak stress-strain curve becomes steeper as JI increases since the contribution of the new SBs undergoing strain-softening behavior to axial strain of JR increases with JI. For the moderate JI, the lower strength and ideal plastic behavior beyond the elastic stage are found, reflecting that the inclined joint governs the deformation of JR. The present numerical prediction on anisotropic peak strength in plane strain compression qualitatively agrees with triaxial experimental tests of many kinds of rocks. Comparison of the present numerical prediction on JI corresponding to the minimum peak strength of JR and the oversimplified theoretical result by Jaeger shows that Jaeger’s formula has overestimated the value of JI.
Authors: Yuriy Perlovich, Margarita Isaenkova, Vladimir Fesenko, Hans Joachim Bunge
Abstract: The substructure nonuniformity of metal materials with developed deformation texture was studied by use of the X-ray method of Generalized Pole Figures. Main regularities of substructure nonuniformity were revealed for the first time. Substructure conditions of grains in rolled material form an extremely wide spectrum and vary by passing from texture maxima to texture minima, where residual deformation effects are most significant. The distribution of residual elastic microstrains in the orientational space of rolled material shows the distinct cross-wise system, consisting in alternation of quadrants with predominant microstrains of opposite signs.

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