Single Crystal Texture Research Articles

Development of microstructure and texture during rolling of single-phase and two-phase cube-oriented Al-Cu single crystals

With regard to the texture control in commercial Al-sheet products, the evolution of the cube-orientation (001)[100] during deformation and subsequent recrystallization is of particular interest, because this orientation is known to strongly affect sheet formability and mechanical properties. The deformation behavior of two-phase Al-alloys is known to be strongly affected by the presence of second-phase particles. It was the aim of the present study to attain insight into the influence of particles on the evolution of microstructure and texture during rolling of cube-oriented single crystals. Particular emphasis was put on the correlation of the local orientations in the deformation zones around the particles with the matrix orientation. Complementary work on the influence of particles on the microstructure and texture of single crystals with stable rolling texture orientations will be described in a separate paper.

Texture Analysis of LiF Thin Films Evaporated onto Amorphous Substrates at Different Temperatures

Polycrystalline thin LiF films thermally evaporated on amorphous substrates show different crystallite orientations depending on the substrate temperature during evaporation. The recording of direct diffraction pole figure shows that the LiF crystallites present a single crystal texture, which can be described as a 〈522〉 [uvw] texture for high temperature deposition (250 to 300 °C) and as 〈16 9 7〉 [uvw] texture for low temperature (room temperature) substrates. Scanning electron microscopy shows the presence of a globular film structure both for high and low temperature depositions with an average grain size of about 200 to 250 and 130 to 150 nm for high and low temperature evaporations, respectively. By rising the deposition temperature the 〈100〉 LiF crystallographic direction approaches the normal to the substrate plane with an increase of the film refractive index. Polykristalline dünne LiF-Schichten, die auf amorphe Substrate thermisch aufgedampft wurden, zeigen verschiedene kristallographische Orientierungen in Abhängigkeit von der Substrattemperatur. Die Polfiguren zeigen eine Einkristalltextur für alle Proben. Die dünnen LiF-Schichten, die bei hohen Temperaturen (250 bis 300 °C) aufgedampft worden sind, lassen sich als 〈522〉 [uvw]-Texturen eines kubischen Gitters beschreiben, während bei niedrigen Temperaturen (Zimmertemperatur) eine 〈16 9 7〉 [uvw]-Textur aufgewiesen wird. Rasterelektronenmikroskopie-Aufnahmen zeigen eine globulare Struktur der Schichten unabhängig von der Substrattemperatur, mit einer durchschnittlichen Keimgröße von 130 bis 150 nm für Zimmertemperatur bzw. 200 bis 250 nm für 250 bis 300 °C. Die Steigerung der Aufdampftemperatur bewirkt eine Orientierungsänderung der LiF-Kristalle in Richtung der 〈100〉 [uvw]-Textur und eine Zunahme der Brechzahl.

Characterization of aluminum hydroxide particles from the Bayer process using neural network and Bayesian classifiers

An automatic process of isolating and characterizing individual aluminum hydroxide particles from the Bayer process in scanning electron microscope gray-scale images of samples is described. It uses image processing algorithms, neural nets and Bayesian classifiers. As the particles are amorphous and different greatly, there were complex nonlinear decisions and anomalies. The process is in two stages; isolation of particles, and classification of each particle. The isolation process correctly identifies 96.9% of the objects as complete and single particles after a 15.5% rejection of questionable objects. The sample set had a possible 2455 particles taken from 384 256x256-pixel images. Of the 15.5%, 14.2% were correctly rejected. With no rejection the accuracy drops to 91.8% which represents the accuracy of the isolation process alone. The isolated particles are classified by shape, single crystal protrusions, texture, crystal size, and agglomeration. The particle samples were preclassified by a human expert and the data were used to train the five classifiers to embody the expert knowledge. The system was designed to be used as a research tool to determine and study relationships between particle properties and plant parameters in the production of smelting grade alumina by the Bayer process.

Ultrasonic Characterization of Rolling and Recrystallization Textures in Aluminum

Crystallographic texture, which plays an important role in many forming operations, is developed during sheet metal processing. Improved product quality could be achieved if the texture could be measured, quickly and inexpensively, during different stages of the processing. One potential scheme, involving measurement of the angular dependence of the speed of ultrasonic waves propagating in the plane of the sheet is described, as applied to aluminum. While this technique has been successfully used in steel sheets, application to aluminum is more difficult because of the smaller elastic anisotropy of the crystallites. This paper presents the results of a detailed study of the strengths and weaknesses of the approach. Included are discussions of signal processing factors, the accuracy of the ultrasonically determined , and a comparison between measured by ultrasonics and by diffraction techniques (both X‐ray and neutron). It is found that relative velocity measurements are very good for determining and . These measurements can easily distinguish between rolling and recrystallization textures, and can also detect more subtle variations in recrystallization textures. A systematic offset in the prediction of is also reported, which is believed to be a consequence of unknown alloy dependence of the single crystal elastic constants and texture free velocities, quantities which play a key role in inferring this quantity from absolute measurements.

Preparation and characterization of YBa 2Cu 3O 7− x high Tc superconducting thin films deposited by S-gun sputtering

We have prepared YBa 2Cu 3O 7− x high T c superconducting (HTS) thin films on (100) yttria-stabilized zirconia (YSZ) and LaAlO 3 (LAO) substrates, using a 2 kW S-gun in an off-axis mode. By varying the temperature of the substrates, films with a axis and c axis orientations were readily obtained. The X-ray diffraction pattern and Laue pattern confirmed that films with a axis orientation exhibited a single-crystal texture. All films had a good mirror-like surface. For films grown on YSZ substrates, scanning electron microscopy (SEM) revealed a clear distinction between the surfaces of the films grown at various temperatures (520–780°C). Films grown on LAO substrates exhibited even smoother and flatter surfaces. The SEM changes will be discussed in correlation with J c. The best HTS thin films were obtained on LAO substrates at a temperature of 820°C, with T c=89 K and J c=1×10 6 A cm -2 (77 K).

電子線衝撃溶解法によって作製したＴａ単結晶の機械的性質におよぼす結晶方位の影響

Effects of cold roll and compression on Ta single crystals grown by electron beam melting methods were systematically studied.The rolling effect was determined using X-ray techniques and microphotography at successive stages of roll-ing, and the operating slip systems were determind from observations of slip traces on the side and front surfaces rolled. The mean grain size and the mean strain were determined by using the Hall method. The rolling texture was determined by the X-ray pole figure method at successive stages of rolling.Stress-strain curves of various Ta single crystals were obtained in order to clarify the effect of compressive deformation. The following results were obtained: According to the X-ray investigations and surface observa-tions, the mechanical structure of Ta single crystals subject to cold rolling is destroyed in the order, {110}- and , {111}- , and {100}- and .The work-hardening effect of Ta crystals, examined by using compression tests, was determined to be, small and in the order, of directions , and . The cold-rolled texture of Ta single crystals is grouped in {100}- and {111}- orientations, and it is the same as that of Fe single crystals.

Structure and orientation development in biaxial stretching of ultrahigh molecular weight polyethylene gel films

AbstractUltrahigh molecular weight polyethylene (UHMWPE) gel films were prepared by gelation crystallization from decalin solutions. According to wide‐ and small‐angle X‐ray scattering (WAXD and SAXS) studies, single crystal mat texture with crystal c‐axis oriented normal to film surface generally develops. However, randomly oriented structure can also develop if an external force is applied to gel films during gelation crystallization. Both textures invariably yield high drawability in uniaxial mode with outstanding modulus and strength. Biaxial films, typically 5 × 5, 6 × 6, 8 × 8, and 10 × 10 times the original dimensions, were prepared at 130°C–135°C in a biaxial stretcher. Optical microscopic Investigations reveal the development of interwoven fibrillar structure in all specimens. WAXD and SAXS studies show that lamellar structure transforms to fibrillar texture during biaxial stretching. Crystal orientation is characterized by WAXD pole figure and infrared dichroic methods. Mechanical studies suggest that tensile modulus and strength appear uniform. In comparison with uniaxial deformation, significant improvement in the lateral strength is seen in the biaxially stretched films.

Highly oriented single-phase blend films of high- and low-density polyethylene

The microstructures of highly oriented drawn films of blends of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) were investigated by transmission electron microscopy, electron diffraction, X-ray diffraction, and differential scanning calorimetry (DSC). The average crystal size, as well as long period, crystalline content, and melting endotherm peak, decreased as LDPE was added to the blend. When the LDPE content exceeded ∼ 50%, the film texture changed from a single crystal texture to fibre symmetric. Segregation of the two polyethylenes was not detected at low LDPE contents in as-drawn or melted and recrystallized films. In the as-drawn films, a low temperature tail began to appear on endotherm melting peaks at LDPE contents ⩾70%, indicating the onset of segregation. In meltcrystallized films, however, two distinct melting endotherm peaks were visible for LDPE contents ⩾50%. An equilibrium melting point of 141° C and end surface free energy of 101 erg cm−2 (101 × 10−7 J cm−2) were determined by use of the Thomson equation. The close agreement between these values and literature values for HDPE suggested that the crystals present in HDPE/LDPE blends were thermodynamically equivalent to HDPE crystals of equal size, implying that branches were excluded from the crystalline phase.

Direct visualization of microstructure deformation processes in polyethylene

Deformation processes of semicrystalline polymers are highly dependent on microstructure and its orientation, as for example in the different zones of spherulites. The elucidation of the deformation mechanisms is a complex problem, primarily due to the hierarchy of structural features present. Our approach to the determination of the important morphological processes occuring during deformation is to simplify both the sample morphology and the applied stress. The production of near single-crystal texture thin polyethylene (PE) film was made possible by modification of Petermann's method to prepare highly chain axis oriented and planar textured films of high density (HD) PE, in both as-drawn (AD) and annealed (AN) forms. These single crystal texture films were ideal for in situ microscopic deformation studies.HDPE (Marlex 6003 from Phillips Chemical) was melt-drawn from a glass slide at 120°C to form AD films, some of which were then annealed on glycerol at 128°C for two hours.

Atypical textures in quartz veins from the Simplon Fault Zone

Samples of monomineralic quartz veins from the Simplon Fault Zone in southwest Switzerland and north Italy generally have asymmetric, single girdle c-axis patterns similar to textures measured from many other regions. Several samples have characteristically different textures, however, with a strong single c-axis maximum near the intermediate specimen axis Y (the direction within the foliation perpendicular to the lineation X) and a tendency for the other crystal directions to be weakly constrained in their orientation about this dominant c-axis maximum. This results in ‘streaked’ pole figure patterns, with an axis of rotation parallel to the c-axis maximum. These atypical samples also have a distinctive optical microstructure, with advanced recrystallization and grain growth resulting in a strong shape fabric ( S B ) oblique to the dominant regional foliation ( S A ), whereas typical samples have a strong S A fabric outlined by very elongate, only partially recrystallized, ribbon grains. The recrystallized grains of the atypical samples are themselves deformed and show strong undulose extinction and a core-mantle recrystallization structure. The streaked texture is likely to be a direct consequence of lattice bending and kinking during heterogeneous slip on the favoured first-order prism (10 1 0) (a) system, the heterogeneity itself being due to problems in maintaining coherence across grain boundaries when insufficient independent easy-slip systems are available for homogeneous strain by dislocation glide. Such bending would be particularly prevalent in very elongate, thin ribbon grains, resulting in high internal strain energy and promoting recrystallization. Thus both the texture and the microstructure could be significantly modified by later strain increments affecting quartz grains with an already developed, nearly single-crystal texture.

New experiments concerning the mechanism of solid‐state photopolymerization of 2,5‐distyrylpyrazine

AbstractThe photoinduced formation of oligomers in single crystals of 2,5‐distyrylpyrazine (DSP) was investigated by X‐ray and electron diffraction techniques and also by gel permeation chromatography (GPC). The DSP crystals were characterized for the presence and nature of dislocations by dark‐field images and etch‐pit studies. Small angle grain boundaries were identified to be the prominent feature, but in general the crystals were highly perfect. A correlation between the sites of the defects and the formation of the photoproduct could not be detected. The oligomers formed in a solid‐solution under appropriate irradiation conditions. Thus, DSP oligomer of number average degree of polymerization P̄n = 3,2 in macroscopic single crystal texture was obtained for the first time using a laser light source at 478 nm. Deterioration of the single crystal texture of DSP usually observed during photopolymerization is explained as being caused by inhomogeneous light distribution which in turn causes an inhomogeneous product distribution with accumulation of large strain fields. These can be made visible by the multiplication of etch pits. Phase separation between oligomer and polymer is observed on further irradiation of the oligomer single crystals. The oligomer phase seems to play the role of an intermediate in the photopolymerization of DSP at wavelengths λ < 400 nm. The molecular weight distribution of the oligomers was studied by GPC. The data are only compatible with the assumption that the rate constant of dimerization is higher than that for the addition of a monomer to an already existing oligomer.

Dynamical studies of fully oriented deuteropolyethylene by inelastic neturon scattering

Experimental parameters for interchain force fields of polyethylene are measured by neutron triple axis spectrometry and provide some of the first anisotropic information about the forces between carbon chains in simple polymers. Preparation of a bulk specimen of deuteropolyethylene with single crystal texture is reported for the first time. Near Brillouin-zone centre frequencies for both interchain optic and acoustic phonons are derived from neutron scattering studies. These measurements are combined with four frequencies obtained by Raman spectroscopy to give a total of seven experimental parameters for the interchain force field of polyethylene. These are then used to test the available force models. Overall fits of 9 and 19% are provided to these data by two Urey-Bradley force fields. Calculations of the interchain phonon dispersion curves of deuteropolyethylene based on an atom-atom potential parameter model are described. Intermolecular force constants which are derived from an analytical ‘sixexp’ form for the potential between nonbonded atoms are used. These reproduce a wide range of structural and thermodynamic data for many hydrocarbons. This rigid chain model using already fixed parameters fits the observed dynamical data within an average error of 5%. This is significantly better than the fits obtained using the Urey-Bradley force fields with adjustable parameters. The close reproduction of the experimental elastic constants gives support to the calculation of the related elastic moduli perpendicular to the chain axis. Tensile elastic moduli calculated along the two crystallographic axes perpendicular to the chain axis in the orthorhombic cell are very similar, in contrast with earlier predictions. The calculated values of 8 × 10 10 and 9 × 10 10 dyne cm −2 for b and a moduli agree closely with an average interchain modulus de4rived for the crystal from bulk measurements using a two phase ‘sandwich’ model of composite polyethylene.

Variation of yield stress with orientation in oriented polyethylene

AbstractHigh density polyethylene with a single crystal texture has been used to examine the variation of yield stress with orientation in both tension and compression. The Coulomb yield criterion, which has previously been applied to yield data in oriented polyethylene, must be rejected since the experimental data can only be fitted over a limited range of orientation in tension only. The von Mises criterion, as modified by Hill 12 for anisotropic materials, appears to give a reasonably good fit to the tensile data. However, further consideration of the theory with respect to the compressive data shows that the criterion is not applicable. The pressure dependent yield criterion proposed by Caddell et al13 also appears unable to predict the experimentally observed tensile and compressive behaviour. A three‐part criterion previously applied to fibre‐composites 11 gives a good fit to the tensile data; this model also predicts the changeover from ductile to brittle behaviour observed in tensile specimens with θ > 70d̀ (θ is the angle between the tensile axis and the molecular axis). None of the yield criteria examined have been able to explain satisfactorily the lack of any marked degree of anisotropy in compression.

Deformation mechanisms in oriented high density polyethylene

The deformation behaviour of single crystal texture HDPE has been examined in tension as a function of the orientation of the tensile axis with respect to the chain direction. Over most of the orientation range examined, it was found that slip processes parallel to the chain direction were the dominant modes of deformation. Fibrillar slip becomes relatively more important than chain slip as the strain increases and as θ0, the initial value of the angle between the tensile axis and the chain direction, decreases. Lamellar slip was only observed over a limited range of orientations due to the high initiation stress required for the process. At low θ0 values, lamellar separation accounted for a substantial part of the applied strain. Stress-induced martensitic transformation, which was observed in samples with θ0>26°, cannot account for an important fraction of the strain although the resolved shear stress required for the activation of the martensitic transformations is of the same order of magnitude as that required for chain slip.

The vibrational spectrum of polyethylene—III. Polarized Raman spectra of “single crystal texture” polyethylene and a single crystal of C 23H 48

The vibrational spectrum of polyethylene has been widely studied, and is reasonably well understood. However, one of the assignment problems still outstanding is the description of some of the correlation doublets observable in the Raman spectrum of polyethylene at low temperatures. In this paper, using “single crystal texture” polyethylene and a large single crystal of C 23H 48, the symmetry of the components of the B 2g/ B 3g doublets, at Δν $ ̃ 1065 cm −1 and Δν $ ̃ 1295 cm −1, have been unambigously assigned. Combining high resolution and anisotropic data, we support the suggestions of earlier workers as to the origin of the complex band system in the Δν = 1400–1500 cm −1 region of the Raman spectrum. A more rigorous assignment of the vibrational spectrum of linear, crystalline polyethylene, than has hitherto been available, is presented.

Multiple deformation processes in polyethylene single crystals

Abstract Multiple deformation processes operate when polyethylene single crystals are strained in certain directions. The most complicated processes occur when the crystals are strained along the longest of the axes defining the orthorhombic unit cell of polyethylene. At large strains up to six twinning and martensitic transformation processes can operate, and the textures which result have been studied by selected-area electron diffraction. A description and an interpretation of the diffraction patterns are presented. The results are compared with those obtained in a recent study of deformation processes in bulk specimens of high-density polyethylene with a single-crystal texture (Young and Bowden 1974).

The structure and mechanical properties of polyoxymethylene polymerized in the solid state

Polyoxymethylene specimens with single crystal texture were produced by irradiation of needle-shaped trioxane crystals subsequently post-polymerized at fixed temperatures between 30 and 60°C. A clear dependence of polymer conversion on irradiation dose and polymerization temperature was revealed. The polymer morphology consisted of mutually aligned fibrils, half of which were chain-extended crystallites with their molecular axes coincident with the specimen axis. The remaining fibrils consisted of folded chains in a “twin” configuration.

Twinning and martensitic transformations in oriented high-density polyethylene

Abstract The deformation of high-density polyethylene with a single crystal texture by shear in directions perpendicular to the chain direction has been examined by wide-angle X-ray diffraction. It is found that samples can undergo either a martensitic transformation to a monoclinic cell, (100) [010] slip or (110) twinning depending upon the orientation of the specimen to the compression direction. A specific orientation relationship has been found between the new monoclinic cell and the parent orthorhombic cell and this has been compared with relationships found by other workers. Stress-strain curves have been obtained from other specimens and it is suggested that for specimens in certain orientations yield may take place by means of a martensitic transformation at a critical resolved shear stress of 14 ± 1 MNm-2.

Single crystal lamellar texture in a thin-walled cylindrical specimen of polyethylene

Single crystal lamellar texture in a thin-walled cylindrical specimen of polyethylene

The structure of high-density polyethylene with a single-crystal texture

The structure of specially prepared high-density polyethylene with a single-crystal texture has been examined by wide-angle and small-angle X-ray diffraction and by electron microscopy. The bulk of the crystallites in the sample are found to be oriented within 8° of a perfect single-crystal texture. The small-angle X-ray diffraction patterns suggest that lamellar crystals are present oriented approximately perpendicular to the chain direction. Replicas taken from fracture surfaces indicate that the structure fractures cleanly parallel to (100) which, taken together with other evidence, suggests that molecules fold by adjacent re-entry in (100) planes. Etching in fuming nitric acid reveals a lamellar crystal structure which is consistent with that deduced from small-angle X-ray diffraction. Replicas which were taken of etched surfaces after deformation showed crystals which were tilted with respect to the chain direction. This is consistent with the deformation having taken place by [001] chain slip within the lamellae [1].