Heinz Günter Brokmeier

Microstructures, textures and deformation mechanisms in hematite

Abstract Deformation and recrystallization of hematite in iron formations and high-grade ore bodies of the Caue Formation from the Quadrilatero Ferrifero District, Minas Gerais, Brazil, resulted in several types of fabrics, depending on the tectonic and metamorphic imprint. The fabrics vary from randomly oriented granoblastic to strongly oriented lepidoblastic/mylonitic with local development of cataclastic features. Complete pole figures of the crystallographic planes (003)-basal plane; {110}-prism and {104}-rhombohedron were measured on several samples from different areas by means of neutron diffraction revealing a typical crystallographic preferred orientation for the different fabric types. The configuration and intensity of the maxima are directly related to the magnitude of the deformation and the type of response of the ore. The analysis of the textures and microstructures of the iron ores and comparison with experimental deformation data lead us to the conclusion that three main mechanisms are active: basal slip, diffusion processes and anisotropic grain growth. Post-tectonic recrystallization and secondary grain growth did not affect the textures developed during deformation.

StressTextureCalculator: a software tool to extract texture, strain and microstructure information from area‐detector measurements

Modern materials science diffractometers are generally equipped with area detectors that allow a high time efficiency to be achieved by simultaneously collecting the scattering pattern over large angular regions. These area-detector-based instruments, however, produce a huge amount of data, especially if they are located at large-scale neutron or synchrotron sources. The software StressTextureCalculator (STeCa) was designed to facilitate fast, easy and automated access to such area-detector data. Its outstanding features are direct calculation of diffraction patterns from different types of area-detector measurements, automatic data treatment and peak fitting using several implemented fit options. The resulting information on intensity, peak shift and broadening can then be exported into several data formats. These in turn can be used as input for a wide range of texture, stress and microstructure analysis software packages without additional prior treatment.

Modeling of texture evolution in copper under equal channel angular pressing

Abstract Texture evolution was analyzed with the full-constraint Taylor model for an idealized perfectly plastic face-centered cubic material as well as for real, strain-hardening copper subjected to equal channel angular pressing (ECAP). For the idealized material, the stress in the plastically deformed part of the billet was shown to be uniform leading to complete filling of the die. Finite element simulations showed that plastic deformation is localized in a narrow shear zone and that the plastic strain and texture in the billet become uniform after ECAP. A simplified recipe for texture calculation akin to that proposed by Gholinia et al. was suggested: it reduces the deformation under ECAP to a combination of two rotations separated by tension-compression. For the case of copper, a strain hardening model based on dislocation density evolution was used. It was shown that due to significant strain hardening during the first ECAP pass, the flowing material does not fill the outside die corner and a strai...

Microstructure, texture and mechanical properties of the magnesium alloy AZ31 processed by ECAP

Abstract To investigate the influence of equal channel angular pressing on the microstructure and texture of the magnesium alloy AZ31, electron backscattering diffraction and well as neutron diffraction experiments were carried out. Through these experiments it was possible to trace the microstructure and texture evolution with strain accumulated with the increasing number of equal channel angular pressing passes. It was further demonstrated by subsequent compression tests that the microstructural changes produced by equal channel angular pressing have a beneficial effect on both the compressive strength and ductility of AZ31.

Synchrotron Radiation Investigation of Twinning in Extruded Magnesium Alloy AZ3l

The crystallographic response to deformation – texture evolution, internal elastic strain, and twin evolution – was measured for three load/orientation variants for AZ31 magnesium alloy extrudate tested in-situ in a synchrotron beamline. Specimens were loaded in tension parallel to the extrudate transverse direction, in compression along the same axis, and in compression parallel to the extrudate normal direction. The crystallographic responses are correlated with the mechanical behaviour of the extrudate.

Neutron diffraction texture analysis

Abstract Due to the high transmission of neutrons for most materials, neutron diffraction is an efficient tool for the analysis of bulk textures of polycrystalline materials. The main applications are pole-figure measurements of coarse-grained materials, non-destructive measurements of identical samples at different states, investigations of unprepared natural samples, analysis of rather weak textures and the measurements of multi-phase systems. Neutron texture analysis was carried out in materials science as well as in geoscience. Recent upgrades in instrumentation allow the texture analysis at temperatures up to 1100°C and the texture investigation under load.

The new loading device for texture measurement on the neutron diffractometer TEX-2

A special device for tensile and compressive loading installed on a neutron texture diffractometer has been developed. The wide range of suitable sample dimensions and loading parameters are described. This new device now allows the influence of applied forces on the texture to be investigated by neutron texture measurement. Results achieved under tensile loading are presented.

Structure and Crystallographic Texture of Arthropod Bio-Composites

In this study we present experimental investigations on the microscopic structure, constituent phases, and crystallographic textures of the exoskeleton of three types of decapod crustaceans, namely, lobster, crab, and horseshoe crab. The carapace of such animals is a biological multiphase nano-composite consisting of an organic matrix (crystalline chitin and non-crystalline proteins) and biominerals (calcite, phosphate). The synchrotron measurements of the crystalline chitin and of the biominerals which are embedded in the chitin-protein matrix (in case of lobster and crab) reveal strong textures. The horseshoe crab does not seem to contain notable amounts of crystalline minerals. The Debye-Scherrer images of the lobster specimen suggest that the biominerals form clusters of crystals with similar crystallographic orientation. TEM images support this suggestion. The crystallographic texture of the chitin is arranged with its longest cell axis parallel to the normal of the surface of the exoskeleton.

Texture Formation during ECAP of Aluminum Alloy AA 5109

The technical aluminum alloy AA 5109 with a strong cube rolling texture has been deformed at room temperature by equal channel angular pressing (ECAP) using three passes of route A. Samples for ECAP have been cut parallel and at 45° with respect to the rolling direction yielding different starting textures. The local texture after ECAP has been investigated by highenergy synchrotron radiation. It is characterized by typical shear components of face-centred cubic (fcc) metals which deviate from their ideal positions. The texture with respect to intensity and deviation from ideal positions of the components depends on the distance from the top of the extruded billet and changes from pass to pass. It is also strongly influenced by the starting texture. The texture gradient has been discussed in the light of Tóth’s flow line model. The texture results have also been compared with those of other fcc metals with different stacking fault energy.

Texture induced plastic anisotropy of NiAl polycrystals

Abstract Textured stoichiometric NiAl polycrystals have been deformed in compression at room temperature under 0.4 GPa confining pressure at a strain rate of about 10 −4 s −1 . The strength of the samples depends on the preferred orientation with respect to the compression axis, with 〈100〉 being much harder than those with 〈110〉 and 〈111〉. Similarly, the frequency of intercrystalline microcracking shows the same tendency. The orientation distribution of the microcracks indicates that they mainly result from internal stresses released after unloading. The plastic anisotropy at elevated strains correlates with the Taylor energy calculated. The deviation from axially symmetric deformation is due to the tendency of minimizing the Taylor energy.