Preferred Orientation Texture Research Articles

Biomineral crystallographic preferred orientation in Solenogastres molluscs (Aplacophora) is controlled by organic templating

Aplacophoran molluscs are shell-less and have a worm-like body which is covered by biomineralized sclerites. We investigated sclerite crystallography and the sclerite mosaic of the Solenogastres species Dorymenia sarsii, Anamenia gorgonophila, and Simrothiella margaritacea with electron-backscattered-diffraction (EBSD), laser-confocal-microscopy and FE-SEM imaging. The soft tissue of the molluscs is covered by spicule-shaped, aragonitic sclerites. These are sub-parallel to the soft body of the organism. We find, for all three species, that individual sclerites are untwinned aragonite single crystals. For individual sclerites, aragonite c-axis is parallel to the morphological, long axis of the sclerite. Aragonite a- and b-axes are perpendicular to sclerite aragonite c-axis. For the scleritomes of the investigated species we find different sclerite and aragonite crystal arrangement patterns. For the A. gorgonophila scleritome, sclerite assembly is disordered such that sclerites with their morphological, long axis (always the aragonite c-axis) are pointing in many different directions, being, more or less, tangential to cuticle surface. For D. sarsii, the sclerite axes (equal to aragonite c-axes) show a stronger tendency to parallel arrangement, while for S. margaritacea, sclerite and aragonite organization is strongly structured into sequential rows of orthogonally alternating sclerite directions. The different arrangements are well reflected in the structured orientational distributions of aragonite a-, b-, c-axes across the EBSD-mapped parts of the scleritomes. We discuss that morphological and crystallographic preferred orientation (texture) is not generated by competitive growth selection (the crystals are not in contact), but is determined by templating on organic matter of the sclerite-secreting epithelial cells and associated papillae.

Growth of Zn1−xNixO Thin Films and Their Structural, Optical and Magneto-Optical Properties

The radio frequency (RF) reactive sputtering technique has been used to prepare Zn1−xNixO thin films with 0 ≤ x ≤ 0.08. Composite targets were obtained by mixing and pressing NiO and ZnO powders. Sapphire, quartz and glass were used as substrates. X-ray diffraction analysis of Ni-doped ZnO films indicates that all samples are crystalised in a hexagonal wurtzite structure with a preferred orientation along the (002) plane. Any secondary phase, corresponding to metallic nickel clusters or nickel oxides was not observed. High-resolution transmission electron microscopy (HR-TEM) image observed for Zn1−xNixO thin film shows a strong preferred orientation (texture) of crystalline columns in the direction perpendicular to the substrate surface. Different surface morphology was revealed in AFM images depending on the film composition and growth condition. Optical absorption spectra suggest the substitution of Zn2+ ions in the ZnO lattice by Ni2+ ions. The energy bandgap value was also found a complex dependence with an increase in Ni dopant concentration. In photoluminescence spectra, two main peaks were revealed, which are ascribed to near band gap emission and vacancy or defect states. Faraday rotation demonstrates its enhancement and growth of ferromagnetism with the increase in Ni content of Zn1−xNixO thin films at room temperature.

Investigation on Microstructures and High-Temperature Oxidation Resistance of Cr Coatings on Zircaloy-4 by Multi-Arc Ion Plating Technology.

Introducing the oxidation-resistant coating on Zr alloy is considered to be one of the potential solutions for accident-tolerant fuel (ATF) materials. In this study, pure Cr coatings were prepared on a Zircaloy-4 (Zry-4) alloy surface by multi-arc ion plating under different process parameters. The ability of Cr coating on Zry-4 alloy cladding to improve the oxidation resistance to prevent a loss-of-coolant accident (LOCA) was studied. The microstructure of Cr coating was analyzed using the EBSD technique, and the high-temperature steam oxidation was tested at 800, 1000 and 1200 °C. Compared with the original Zry-4 alloy, the samples with Cr coatings exhibited much better oxidation resistance under different high-temperature steam oxidation conditions. However, the Cr coating exhibited columnar grain, strong preferred orientation and (001) fiber texture. The columnar grain boundaries provided paths for the diffusion of oxygen atoms to the Zry-4 alloy matrix at high temperatures. The results showed that the oxidation film of Cr coating with relatively random grain orientation was compact and uniform and exhibited the best oxidation resistance at high temperatures.

Yield strength of CeO2 measured from static compression in a radial diamond anvil cell

Cerium oxide (ceria, CeO2) is frequently used as a standard in applications such as synchrotron and x-ray free electron lasers for calibrating x-ray wavelengths and offers the potential for understanding the high pressure properties and deformation mechanisms in a wide range of similar face centered cubic (fcc) materials. In this study, the pressure dependence of the strength of ceria was investigated up to 38 GPa using angle dispersive x-ray diffraction in a radial geometry in a diamond anvil cell. In this experiment, the difference in the stress along the axis of compression and perpendicular to the direction of compression can be determined, giving a quantity known as the differential stress. It was found that the differential stress (t), a measure of the lower bound for yield strength, initially increases rapidly from 0.35 ± 0.06 GPa to 2.2 ± 0.4 GPa at pressures of 1.8 and 3.8 GPa, respectively. Above 4 GPa, t increases more slowly to 13.8 ± 2.6 GPa at a pressure of 38 GPa. The changes in the preferred orientation (texture) of CeO2 with pressure were also measured, allowing for the determination of active deformation mechanisms using an elasto-viscoplastic self-consistent model (EVPSC). It was found that as pressure increased, the [001] direction had a slight preferred orientation along the axis of compression. Our EVPSC model of experimental fiber (cylindrically symmetric) textures and lattice strains were most consistent with dominant slip activity along {111}⟨11¯0⟩.

Investigation on the robust boronizing strategy for the surface strengthening of CoCrNi medium-entropy alloy

Boronizing has been considered as a promising strategy to enhance the surface hardness and corrosion resistance of the new emerged alloys, like CoCrNi medium-entropy alloy (MEA). However, recent studies showed that a brittle silicide layer was generated on the surface for Ni-containing alloys boronizied with the SiC-containing powder (SiC+KBF4+B4C). In this study, Si-free powder packing (900 °C 4 h) and electrochemical boronizing (900 °C 30 min) methods were explored to obtain the boronized layer for CoCrNi MEA. The morphology, element distributions and phases of the boronized layer were characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS) and X-ray diffraction (XRD). The results show that the powder-pack boronizing method with 90 wt% B4C + 10 wt% NaBF4 (B4C) and electrochemical (EC) methods have the thickest boronized layer (~70 μm) with hardness of about 22 GPa. The boronized layer is dominated by columnar CrB and Co2B with obvious preferred orientation and strong texture. In addition, CoB, Ni2B and Ni3B also exists in the boronized layer, and these two optimal boronizing processes avoid the influence of Si. This study shows that the B4C and EC boronizing methods can be considered as the viable alternative strategy for the preparation of strengthened layers.

Characterizing the microstructural anisotropy of fine-grained phyllosilicate-rich rocks

Abstract. The physical properties of claystones, shales, and slates are highly dependent on the alignment of phyllosilicate minerals. With increasing overburdening, the shape and the crystallographic preferred orientation of these minerals are affected by uniaxial shortening as well as tectonic processes including recrystallization under elevated pressure and temperature conditions. The microstructural anisotropy expressed mainly by the alignment of phyllosilicates significantly predetermines the orientation of fractures, hence the shear strength and stability of clay-rich sediments and rocks. A quantitative analysis of phyllosilicate alignment is therefore essential to evaluate the properties and the mechanical behavior of these rocks. This can be carried out by analyzing the crystallographic preferred orientation (texture). Although texture analysis is a common tool in geosciences, it becomes more difficult in fine-grained rocks owing to for example particle size, heterogeneity, the polyphase composition, and difficulties in sample preparation. Methods such as electron backscatter diffraction, neutron diffraction, or laboratory X-ray diffraction are restricted with respect to preparation artifacts, sampling size and statistics, water content, etc. To overcome these issues, we successfully apply high-energy X-ray diffraction as available at synchrotron research facilities, e.g., at the German Electron Synchrotron Facility (DESY) in Hamburg, Germany, or the European Synchrotron Research Facility (ESRF) in Grenoble, France. In combination with Rietveld refinement we analyze the bulk texture of phyllosilicate-rich rocks. Here we present the results of texture analysis from a wide range of these rocks: Pleistocene poorly consolidated mud (rocks), affected only by sedimentation and burial; more highly consolidated but tectonically largely unaffected Jurassic claystone from the Opalinus Formation of the Swabian Alb; Carboniferous shales from the Harz mountains representing low-grade metamorphic and deformed rocks. Our methodical approach to quantifying the microstructural anisotropy using texture analysis in fine-grained rocks allows for the quantification of physical properties resulting from the alignment of phyllosilicates. Furthermore, it enables the prediction of direction-dependent mechanical strength, which is crucial for the establishment of long-term repositories for radioactive waste in shales and claystones.

The role of microstructural characteristics of additively manufactured Alloy 718 on tool wear in machining

This study aims to provide a fundamental understanding of the role of microstructural characteristics influencing tool wear when machining Alloy 718 fabricated using Powder Bed Fusion (PBF). The effects of preferred crystallographic orientation (texture), shape and distribution of grains, local misorientation, type and amount of precipitates as well as the type, size and amount of abrasive carbides, nitrides and oxides on tool wear are investigated in as-built condition and after the standard solutionising and double-aging treatment. The microstructures of workpiece materials and the surfaces of worn tools were examined using different material characterisation techniques, including Scanning Electron Microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD). A dislocation-based approach was used to reveal the cumulative effects of the microstructural characteristics on deformation behaviour and the thermo-mechanical loads on the tools during cutting. The analyses suggest that texture and the extent of material work-hardening prior to the onset of crack formation markedly influence the amount of plastic work and thus heat generation when machining Electron Beam Powder Bed Fusion (EB-PBF) material. The higher heat generation in the cutting zones provokes thermally-induced wear mechanisms like diffusion-dissolution and oxidation. In addition, the larger amount of hard oxide inclusions present in EB-PBF material leads to higher wear by abrasion. In contrast to the prevailing experimental approaches in this field, the present investigation is built on a physics-based framework to understand the fundamental aspects that govern material deformation and heat generation in cutting and, consequently, tool wear mechanisms. This framework can be used for machinability assessment of any alloy manufactured by different additive manufacturing (AM) technologies and for optimising the process-chain, including printing strategies and thermal post-treatments, to improve the machinability of AM alloys by tailoring their microstructure.

Microstructure and texture evolution during the manufacturing of in situ TiC-NiCr cermet through selective laser melting process

The effects of different selective laser melting (SLM) scan speeds (150 mm.s−1, 95 mm.s−1, 60 mm.s−1, 55 mm.s−1, and 50 mm.s−1) on the microstructure and texture evolution of in situ TiC-NiCr cermet were investigated in the present study. The rotating scan strategy of 60° rotation (Rot-scan) was used to print the samples. Microstructural evolutions were investigated using scanning electron microscopy (SEM). Electron backscatter diffraction (EBSD) and X-ray diffraction analyses were used to identify the micro- and macro-crystallographic preferred orientation (texture). According to the results, the in situ formation of TiC via exothermic reaction resulted in different directions of temperature gradient in the melt pool. Consequently, nucleation and growth occurred in various directions. However, α-fiber texture could be observed in the orientation distribution function (ODF) of the manufactured specimens.

Analysis of in vitro demineralised human enamel using multi-scale correlative optical and scanning electron microscopy, and high-resolution synchrotron wide-angle X-ray scattering

Enamel caries is a highly prevalent worldwide disease that involves the demineralisation of the outer tooth structure. In this study, we report the analysis of artificially demineralised human enamel sections (‘slices’) etched using lactic acid (2% v/v) in comparison with healthy enamel using correlative techniques of optical and electron microscopy, as well as scanning diffraction. Demineralisation of the enamel was characterised at the micron to sub-micron scale. The structure of the healthy enamel was investigated using Focused Ion Beam - Scanning Electron Microscopy (FIB-SEM) and compared with an etched sample to reveal their structural differences. Additional chemical analysis using energy-dispersive X-ray spectroscopy (EDS) was performed and a decrease in the Ca/P atomic % ratio was found in etched samples in comparison with healthy enamel, suggesting greater loss of calcium compared with phosphorus. Synchrotron wide-angle X-ray scattering (WAXS) was performed on the samples to reveal the differences in the diffraction patterns before and after etching in terms of lattice structure and preferred orientation (texture). Texture maps were extracted from diffraction analysis at 500 nm spatial resolution. These maps were correlated with the dimension of the enamel structure. The multi-scale correlative approach provided insights into the demineralisation-induced enamel structure alteration at a resolution approaching 500 nm.

Effect of diverse Pechini sol-gel parameters on the size, morphology, structural and optical properties of the Tenorite (CuO) NPs: A facile approach for desired properties

Copper oxide (CuO) nanoparticles (NPs) have been successfully synthesized by the Pechini sol-gel approach. The effect of three fundamental synthesis parameters on the size, morphology, structural, and optical properties of the prepared products was systematically investigated. The prepared powders were evaluated by XRD, FTIR, DSC/TG, FE-SEM, TEM, and EDS analyses. Based on these experiments, the monoclinic phase structure of highly pure CuO NPs with space group C2/c was characterized. A wide range of crystallite size from 19.1 nm to 45.7 nm were obtained via diverse compositions and calcination temperatures. The preferred orientation (Texture) was found to be altered from (311) to (020). Structural quantities were calculated by Rietveld analysis. Microstructural observations demonstrated that the different morphologies of the CuO NPs (spherical, semi-spherical, and plate-like decorated by semi-spherical NPs) can be achieved by controlling the synthesis parameters. The optical properties of the prepared samples were studied by UV–vis spectroscopy. The estimated direct band gap was decreased from 4.17 eV to 3.01 eV by increasing temperature values. It was found that the size, morphology, texture, and consequently properties of the prepared CuO nanostructures can be controlled by changing the Pechini process parameters.

Micromechanical response quantification using high-energy X-rays during phase transformations in additively manufactured 17-4 stainless steel

Recent studies of additively manufactured (AM) 17-4 stainless steel produced via laser powder bed fusion of nitrogen atomized powders have been found to contain large volume fractions of austenite (γ) compared with the fully martensitic (α') microstructure of wrought 17-4. These AM 17-4 stainless steels have metastable microstructures that transform from a mixed phase composition to predominantly martensitic during deformation. This transformation process, combined with strong preferred crystallographic orientation (texture) that arises during building, produces complex micromechanical interactions that dictate the macroscopic response. Here, high-energy X-ray diffraction performed at a synchrotron light source is used to quantify the volume fraction of austenite and martensite, texture, and the complete orientation dependence of lattice strain (strain pole figures) at various macroscopic strains levels in-situ during uniaxial tension of AM 17-4. Results from wrought 17-4 are also shown for comparison. Initial martensite volume fraction of the stress-relieved AM specimen was measured to be 0.46 and increased to 0.88 after the application of a macroscopic strain of 0.03. During the transformation process, minimal crystallographic texture evolution was observed in either the γ austenite or α' martensite. The distribution of strains in the specimen is found to be heavily influenced by both the transformation process and the initial texture. Phase transformation is found to generate tensile strains perpendicular to the applied load in untransformed γ austenite, while texture is found to produce high heterogeneity of lattice strains within lattice plane families.

Quantitative comparison of microfabric and magnetic fabric in black shales from the Appalachian plateau (western Pennsylvania, U.S.A.)

Anisotropy of magnetic susceptibility (AMS) has been shown to be a good proxy for crystallographic preferred orientation (texture). However, it is not clear in detail how different factors, e.g. modal composition and preferred orientation, define the total AMS in a rock. Black shale samples from a drill core on the Appalachian Plateau in western Pennsylvania were analyzed with respect to their microfabric as determined by texture and microstructure, and AMS. Low- and high-field AMS, which was measured at room temperature, reveals that the AMS of the samples is dominated by the para- and diamagnetic phases. Synchrotron diffraction was applied to determine the texture of all relevant mineral phases incorporated in the samples. Muscovite and chlorite pole figures show single maxima perpendicular to the foliation, reflecting dominant flattening strain. From these textures and the modal compositions, AMS models were calculated using the intrinsic magnetic anisotropy of the single crystals. The modeled and measured AMS are comparable in terms of their principal directions and shapes of the anisotropy ellipsoid for the dominantly paramagnetic samples, with the maximum susceptibility axes oriented subhorizontal to the NE-SW. Both, textures and AMS, indicate that the samples have undergone largely bedding compaction with a weak tectonic overprint linked to the Alleghenian orogeny. Our results suggest that the microfabric and the magnetic fabrics on the plateau, 200 km away from the Allegheny Front, detect the tectonic shortening. The AMS modeling demonstrates how the contribution of the intrinsic AMS of each mineral controls the AMS of the whole rock.

Anisotropy of nickel-based superalloy K418 fabricated by selective laser melting

Selective laser melting (SLM) is a promising additive manufacturing (AM) technology for fabricating the near net-shaped parts by selectively melting and solidifying a thin powder layer with a high-intensity laser beam according to the CAD data for arbitrary components. In this work, Ni-based superalloy K418 samples were fabricated by selective laser melting (SLM). To evaluate the anisotropic mechanical behavior of the SLM processed K418 samples with layer-by-layer melting, the samples were manufactured parallel (transverse specimens) and vertical (longitudinal specimens) to the building direction on the substrate. The microstructural anisotropy analysis was performed by optical microscopy (OM) and scanning electron microscopy (SEM). Electron backscatter diffraction (EBSD) analysis was used to identify their crystallographic preferred orientation (texture) and to correlate the anisotropy of the mechanical strength with the texture of the material. The results showed that the transverse specimens had slightly higher yield strength, but much significantly higher ductility than that of the transverse specimens with the elongated columnar grains along the building direction.

Influence of Nb Microaddition on Microstructure and Texture Evolution in a Fe-21Mn-1.3Al-1.5Si-0.5C TWIP Steel under Uniaxial Hot-Tensile Conditions

ABSTRACTAdvanced high-strength steels as Twinning Induced Plasticity (TWIP) steels have been developed using microalloying elements and subsequent thermo-mechanical processing techniques. Moreover, under hot-working conditions, these steels undergo significant microstructural changes as a result of preferred crystallographic orientation (texture) of grains. In order to evaluate this behavior, one non-microalloyed and other single Nb-microalloyed TWIP steels were melted in an induction furnace and cast into metal and sand molds. Samples with austenitic grain sizes between 400 and 2000 µm were deformed at 800 °C and strained at a constant strain rate of 10-3 s-1, and deformation state was examined by means of electron backscatter diffraction (EBSD) technique near to the fracture tip. It was found that non-microalloyed TWIP steel solidified in both metal and sand mold exhibits dynamically recrystallized grains. On the other hand, Nb microaddition has a strong influence in TWIP steel retarding the onset of recrystallization kinetics, showing low angle sub-structured grains. Furthermore, it was possible identifying the crystallographic orientation of grains using the inverse pole figures (IPF) and the orientation distribution function (ODF). Weak cube {001}<100> recrystallization and E{111}<110> γ-fiber deformation textures components were detected.

Relationship between electrical properties and crystallization of indium oxide thin films using ex-situ grazing-incidence wide-angle x-ray scattering

Grazing-incidence, wide-angle x-ray scattering measurements were conducted on indium oxide thin films grown on silica substrates via pulsed laser deposition. Growth temperatures (TG) in this study ranged from −50 °C to 600 °C, in order to investigate the thermal effects on the film structure and its spatial homogeneity, as well as their relationship to electrical properties. Films grown below room temperature were amorphous, while films prepared at TG = 25 °C and above crystallized in the cubic bixbyite structure, and their crystalline fraction increased with deposition temperature. The electrical conductivity (σ) and electrical mobility (μ) were strongly enhanced at low deposition temperatures. For TG = 25 °C and 50 °C, a strong ⟨100⟩ preferred orientation (texture) occurred, but it decreased as the deposition temperature, and consequential crystallinity, increased. Higher variations in texture coefficients and in lattice parameters were measured at the film surface compared to the interior of the film, indicating strong microstructural gradients. At low crystallinity, the in-plane lattice spacing expanded, while the out-of-plane spacing contracted, and those values merged at TG = 400 °C, where high μ was measured. This directional difference in lattice spacing, or deviatoric strain, was linear as a function of both deposition temperature and the degree of crystallinity. The crystalline sample with TG = 100 °C had the lowest mobility, as well as film diffraction peaks which split into doublets. The deviatoric strains from these doublet peaks differ by a factor of four, supporting the presence of both a microstructure and strain gradient in this film. More isotropic films exhibit larger μ values, indicating that the microstructure directly correlates with electrical properties. These results provide valuable insights that can help to improve the desirable properties of indium oxide, as well as other transparent conducting oxides.

The Mechanical Behavior of HAVAR Foils Using the Small Punch Technique.

Prediction of the mechanical behavior of thin foils (~25 µm) requires special characterization techniques. The current work is focused on the mechanical and microstructural characterization of 25 µm HAVAR alloy foils following annealing, cold rolling, and subsequent heat treatments, using small punch testing (SPT), X-ray diffraction (XRD), and transmission-scanning electron microscopy (TEM). The SPT technique revealed that the annealed specimens exhibited the largest maximal load to failure and deformation (more than two-fold), compared to the cold rolled and heat treated conditions. The microscopy observations revealed high dislocation density following cold rolling and subsequent heat treatments. Following annealing, a cubic crystallographic structure (FCC) with equiaxed grains and a limited dislocation population was observed. Following cold rolling and subsequent thermal treatment, a preferred orientation texture (i.e., ‘deformation texture’) was observed with a very high dislocation density. The correlation between the mechanical behavior and the microstructural observations is discussed in detail.

Investigations into the phase composition of zirconia-based sinters with an axial texture

Owing to the phase transition of the tetragonal form of ZrO2 into the monoclinic one, caused by mechanical stresses, preparation of powder samples for quantitative phase analysis by the X-ray diffraction method should be avoided. The process of grinding of zirconia sinters leads to considerable changes in their phase composition. For this reason, a quantitative phase analysis should be conducted on solid samples not subjected to mechanical stresses, irrespective of problems appearing during experiments and analysis. One such problem is preferred crystallographic orientation (texture). This paper describes the influence of a preferred crystallographic orientation on the quantitative phase analysis conducted on solid samples and presents the results of an analysis in which corrections for uniaxial and multiaxial textures were applied. It was found that the examined samples had a very weak but nonzero multiaxial texture. The share of the randomly oriented fraction in the examined sinters was determined to be ca 94 vol.% and the share of the textured fraction ca 6 vol.%. From the statistical point of view, in the case of small amounts of the textured fraction, a correction on one distinguished crystallographic plane can overcome this problem. In the case of the slightly textured sinters of metering nozzles subjected to investigation here, the correction related to all the unique directions was statistically insignificant because the textured part corresponds to only a small volume fraction. However, corrections related to all texture axes considerably improve the fit of the calculated X-ray pattern with the experimental one and help to better characterize the examined materials.

On the Crystallography of Silver Nanoparticles with Different Shapes

The crystallographic properties of silver nanoparticles with different morphologies (two different kinds of spheres, cubes, platelets, and rods) were derived from X-ray powder diffraction and electron microscopy. The size of the metallic particle core was determined by scanning electron microscopy, and the colloidal stability and the hydrodynamic particle diameter were analyzed by dynamic light scattering. The preferred crystallographic orientation (texture) as obtained by X-ray powder diffraction, including pole figure analysis, and high resolution transmission electron microscopy showed the crystallographic nature of the spheres (almost no texture), the cubes (terminated by {100} faces), the platelets (terminated by {111} faces), and the rods (grown from pentagonal twins along [110] and terminated by {100} faces). The crystallite size was determined by Rietveld refinement of X-ray powder diffraction data and agreed well with the transmission electron microscopic data.

Crystallography and Textural Aspects of Crossed Lamellar Layers in Arcidae (Bivalvia, Mollusca) Shells

Bivalve shell microstructures are important traits that can be used for evolutionary and phylogenetic studies. Here we examine the crossed lamellar layers forming the shells of the arcoids, Arca noae, Glycymeris glycymeris and Glycymeris nummaria in order to better understand the crystallography of this complex biomaterial. Textural aspects and crystallography of the outer crossed lamellar layer of these species have been clarified using high-resolution electron microscopy and X-ray diffraction (XRD) techniques. These shells are made of aragonite crystals in a crossed lamellar arrangement with a high preferred crystal orientation (texture). The distribution of maxima in the pole figures implies that there is not a single crystallographic pattern within the measured area, but a continuous variation between two classes of distinct patterns. In the first of these, there is a set of four crystal orientations (referred to as upper set). These four crystal orientations are distributed in two pairs (which are coplanar), with the crystals of each pair being twinned on {110}. The pairs are tilted with respect to each other by approximately 20-40º around an axis perpendicular to the {110} common twinning plane. In the second pattern (referred to as lower set), the crystal orientations of each pair are rotated around a <–110> direction until the a-axes of the diametrically opposing crystal orientations of two different twinned pairs become parallel. As a result of this rotation, in the lower set the crystal orientations no longer form pairs twinned on {110}.These crystallographic relationships are unknown in inorganic aragonite. Our results are similar to those reported for the neogastropod Conus marmoreus. Thus, the common crossed lamellar crystallography in the arcoid bivalves and in C. marmoreus is a striking example of convergence in the development of crossed lamellar microstructures.

Study of deformation texture in an AZ31 magnesium alloy rolled at wide range of rolling speed and reductions

The plasticity of Mg is restricted at low temperatures because: (a) only a small number of deformation mechanisms can be activated, and (b) a preferred crystallographic orientation (texture) develops in wrought alloys, especially in flat-rolled sheets. This causes problems in thin sheet processing as well as component manufacturing from the sheet. In this study, different rolling speeds from 15 to 1000 m/min were employed to warm-roll AZ31B magnesium alloy to different reductions. The results show that AZ31B sheets rolled at 15 m/min and 100 °C has fractured for reductions of more than 30% per pass. However, by increasing the rolling speed to 1000 m/min the rollability was improved significantly and the material can be rolled to reductions of more than 70% per pass. The results show that with increasing strain rate at 100°C, the splitting of basal poles was observed, indicating the activation of more contraction twins and secondary twins.