Showing papers on "Texture (crystalline) published in 1971"

Identification of structural processes in deformation of oriented polyethylene

Abstract: The investigation is concerned with the relation between changes in the submicroscopic structure, as revealed by low angle X-ray scattering in combination with the usual wide angle X-ray diffraction, and changes in the macroscopic sample dimensions during the deformation of oriented low density polyethylene. The samples examined are mainly drawn and rolled sheets possessing a double crystal texture, with a limited additional study on a drawn sample with fibre symmetry and on recently discovered single texture specimens. The deformations include tension and compression along selected sample directions applied mostly at room temperature, but also at various elevated temperatures. The salient feature of most of these experiments is the identity of the macroscopic strain and the changes in the submicroscopic periodicity along the direction in which the sample has been initially oriented. Even when this identity is not obeyed, as for deformation at the highest temperatures, a proportionality between the quantities concerned is always maintained. It is demonstrated how the changes in the structural periodicity can be subdivided into a rotation of unaltered crystallites, interpreted as interlamellar slip, into a change in chain inclination within the crystallites, interpreted as intralamellar slip, and into a change in the separation of the crystallites which includes the extension or compression of interlamellar amorphous material. It is shown that the relative contributions of each of these three effects is a function of the temperature of the deformation, the sample type and the type of stress applied. The results are evaluated and discussed in terms of existing conceptions of an oriented polymer and are related to earlier findings on this subject. It is pointed out in particular that the samples in question represent a very simple mechanical system: a series coupling of the individual structural processes involved suffices to describe the response of the sample to externally imposed stress. The identity relation between changes in structure and macroscopic sample dimensions is also revealed by swelling experiments. This, in addition to equating changes in lamellar separation with changes in sample dimension, also provides some definitive information on the location of the swelling agent.

Light-Scattering Patterns from Collagen Films in Relation to the Texture of a Random Assembly of Anisotropic Rods in Three Dimensions

Abstract: Polarized light scattering from several types of collagen films cast from an acid soluble collagen and solubilized collagens by proteolitic enzyme (except callagenase) and from denatured films under various conditions, was observed under Hv and Vv polarization conditions.The scattering patterns from the collagen films were different from those from spherulitic films of polyalphaolefins. The patterns were analyzed in terms of a three-dimentional random assembly model of anisotropic rods resulting in the following conclusions. The polar angle of orientation of scattering elements with respect to the rod axis ranged from 50 to 70°, depending on the type of collagen film. The value of p, which is defined by (α⊥−αs)/(α||−α⊥), changes from very positive in the air-dried state to less positive, zero, or even slightly negative in the swollen state in saline, also depending on the types of collagen film.On the other hand, the characteristic Hv patterns were diminished in intensity with denaturation while the Vv patterns–as well as the wide angle X-ray diffraction pattern–were not changed to the same extent. This suggests that the light scattering from denatured films arises mainly from correlation in density fluctuations rather than that of orientation of local anisotropy; that is, it is suggested that denaturation causes disintegration of the crystalline superstructure rather than of the crystallites. These crystallites are too small in their correlation distance of the orientation fluctuation to give Hv scattering at such small scattering angles as several degrees only.

Growth, Texture, and Surface Morphology of SiC Layers

Abstract: Highly oriented layers were grown on (001) and (111) silicon substrates by the reduction of in an excess of hydrogen at a temperature of 1365°C. Layers up to ≈100µ thick were grown at a rate of 4.3 µ/min. The material was predominantly with a resistivity range of 0.5–34.5 ohm‐cm, n‐type. Laue x‐ray analysis indicated that the degree of preferred orientation varied with thickness and that multiple orientations exist on the (001) silicon substrates. A higher degree of preferred orientation was achieved on the (001) compared to the (111) substrates. At various thicknesses, faceted grains on the order of 1–2µ in diameter were visible using the scanning electron microscope. The fact that oriented growth was achieved at higher than typical CVD rates for epitaxy suggests that detrimental effects such as substrate evaporation or impurity deposition were overcome by the higher deposition rate.

Textures in the Superplastically Deformed Tin-Lead Eutectic Alloy

Abstract: Texture measurements and metallographic studies have been made at various strains in material deformed with initial values of strain-rate sensitivity (m) = 0.2, 0.3, and 0.7. Texture becomes more random with increasing strain in both phases, independent of the value of m. Curved. grain boundaries and grain growth are produced by deformation and scratch-offset studies demonstrate that boundary sliding is occurring. The texture measurements are discussed in terms of the sliding process itself and possible associated accommodation mechanisms, both of which lead to grain rotation and a slow reduction in texture with increasing strain.

Electric-Field-Induced Texture Transformation and Pitch Contraction in a Cholesteric Liquid Crystal

Abstract: D.C. electric-field-induced pitch contraction and a simultaneous transition from the cholesteric plane texture to the focal conic texture were studied microsopically in a mixture of 20% cholesteryl chloride and 80% cholesteryl oleyl carbonate. The texture change is preceded by the formation of a periodic pattern in the plane texture. The decrease in helix pitch p is very small for applied fields less than 25 kV/cm: above this threshold field the decrease if greater: dp/dv = 0.33nm/V. In the latter region the increase in reciprocal pitch length is proportional to the applied field, in aggrement with Meyer's theory. However, the experimental slope is much less than predicted.

Cholesteric Texture Near Tc and in Presence of a Magnetic Field

Abstract: Near the mesomorphic-isotrophic transition tempetature Tc, only very weak clamping forces to occur between the liquid crystal and the glass walls which confine it. We have studied the cholesteric texture near the transition temperature, for two gemotries: (a) In the parallel plate geometry, we have prepared samples where the helical axis has a constant direction parallel to the glass plates. We describe how such a texture is obtained and how interacts with small cholestric spherulites floating in the isotrophic liquid. (b) In the Cano wedge geometry, we describe a new texture which occurs near Tc.

The effect of finishing temperature on the texture and structure of hot rolled 1 pct Si steel

Abstract: An investigation has been made of the effect of finishing temperature on the texture and structure of a commercial, 1 pct Si steel. Finishing temperatures in the range of 1610° to 1280°F were found to produce three types of rolling texture. Texture I, which was close to random, occurred with finishing temperatures in the range 1610° to 1580°F; texture II, which consisted of a strong [011] fiber texture in the rolling direction, occurred with increasing intensity in the range 1580° to 1430°F, while below 1430°F texture III was developed and consisted of the [011] fiber texture together with a strong 〈111〉 fiber texture, with the fiber axis parallel with the sheet normal. It was found that these three types of texture could be related to microstructures which ranged from equiaxed at 1610°F through a duplex recrystallized structure at intermediate temperatures to an elongated “cold worked” structure at the lowest finishing temperature.

The development of the rolling texture in copper measured by neutron diffraction

Abstract: Three-dimensional orientation distribution functions of the crystallites in copper sheets, cold rolled to different degrees of reduction, have been determined using neutron diffraction pole figures. The main features of the textures may be represented by the orientation 'tube' already described in prior publications. Two ranges of rolling reduction can be distinguished, a lower one (30 to 50 %) and a higher one (70 to 95 %) the texture changes of which correspond to those calculated after the Taylor theory. In an intermediate range (50 to 70 %) a different deformation mechanism occurs which leads to an intermediate (001) [110] texture component. It is supposed that anisotropic hardening may have occured in this range.

Light Scattering and Electron Microscopic Characterization of Amylose Films

Abstract: The anisotropic morphology of amylose films is described by solid‐state light‐scattering analysis A wide range of supermolecular structures was found, varying from ``rodlike'' texture for water‐cast films to ``ringed spherulitic'' texture for those cast from dimethyl sulfoxide (DMSO) After treatments, such as alcohol swelling or prolonged exposure at high relative humidity, the DMSO‐cast films undergo significant textural modification which is best characterized by the observed changes in the scattering envelopes Electron microscopy is, in general, in accord with these observations, although the advantage of the light‐scattering method over electron and simple polarization microscopy for characterizing such systems is clearly shown

Day-night mirror

Abstract: This disclosure relates to a day-night or anti-glare mirror formed from a laminate wherein at least one layer is changeable from a condition which permits the transmission of light therethrough to a condition which scatters light incident thereon, thereby greatly reducing the transmission of light therethrough. In one embodiment, this layer is formed of a transparent, soft, yieldably resilient, solid material. A surface with a roughened texture is formed in the soft, yieldably resilient, solid material or a layer adjacent thereto so that when the roughened texture surface is separated from the adjacent surface, transmission of light is greatly reduced by the roughened surface by scattering, and when the roughened texture surface is pressed firmly against the layer adjacent thereto, light is easily transmitted through the composite laminate. Means are disclosed for separating and pressing together the rough textured surface and the surface adjacent thereto.

Comparison of texture of carrots frozen by airblast, food freezant-12 and nitrogen vapor

Abstract: SUMMARY— Carrot sticks were frozen by immersion in Food Freezant-12, in vapor from liquid nitrogen, in a fluidzed bed tunnel and on trays. Those frozen in Food Freezant-12 were the firmest and most crisp. Texture was related to time needed to freeze the carrots. Either a puncture-testing device or shear press can be used to test for firmness.

Influence of mechanical twinning on wire texture in an Al-Mg alloy

Abstract: Wires of an Al−0.9 pct Mg alloy drawn to 96 pct reduction in area were found to exhibit duplex 〈111〉 + 〈100〉 fiber textures. Transmission electron microscopy and selected area electron diffraction revealed that the Ahlborn-Wassermann mechanical twinning mechanism was active in the formation of the 〈100〉 component. The work hardening characteristics of this alloy make it more susceptible to mechanical twinning than a pure metal of similar stacking fault energy. The nature of the boundaries within each texture component and between them is discussed.

Deformation textures of b.c.c. metals (tungsten).

Abstract: A review is given on the texture resulting from swaging and drawing of bcc. metals (e.g., W). A consistent picture of the drawing texture of polycryst. W may serve as a basis for future models of the deformation mechanism. 15 refs. [on SciFinder (R)]

The temperature dependence of the flow-stress of heavily-deformed doped tungsten

Abstract: The flow stress of cold-worked, doped tungsten has been determined in the temperature range from 77°K (liquid nitrogen) to about 800°K. The tungsten specimens were fibrous with a texture in the drawing direction. The measured flow stress was attributed to two components. The temperature independent part is due to a long-range dislocation-dislocation interaction and prevails solely at elevated temperatures. The temperature dependent component was analyzed according to a theory of elastic dipoles interacting in a thermally activated process with dislocations. The Gibbs free activation enthalpy, ΔG0, and the dipole concentration, Cg, derived from that analysis are ΔG0=1.59 eV and Cg=800 at. p.p.m., respectively. From these results an activation volume was calculated and compared to the one measured by strain rate changes. The agreement is very good, suggesting that an elastic dipole-dislocation interaction indeed explains the increase of the flow stress with decreasing temperature. The origin of the elastic dipoles cannot be determined unambiguously from this investigation. The elastic dipoles might, however, be due either to impurity atoms in interstitial solution, such as carbon or nitrogen, or to small agglomerates of these impurities. Both possibilities are within the limits of the concentrations found by chemical analysis.

Structural and electrical properties of sublimed GaAs films

Abstract: A modification of Hudock's method was used to deposit GaAs films on sapphire and on (111) semi-insulating GaAs in vacuum better than 5 × 10 −8 Torr. On sapphire the crystallites increased in size with increasing substrate temperature, from about 0.6 μm at 480°C to 18 μm at 670°C. The degree of preferred orientation (〈111〉 texture) increased with increasing substrate temperature. Essentially single-crystal Laue and reflection electron diffraction patterns were obtained from films deposited at 630–640°C. Thermal-probe and Hall measurements showed that the films on sapphire were p -type with Hall mobility up to 42 cm 2 /V-sec. The electrical properties of the heteroepitaxial films are discussed in terms of the effects of potential barrier at the grain boundaries, space charge regions in the grains, deviation from stoichiometry and compensation of dopants. The homoepitaxial GaAs films were n -type with mobility nearer to the bulk. The higher mobility of these films indicated that hte quality of heteroepitaxial films was limited by the substrate rather than by the deposition method.

On Anisotropy of Growth of Polycrystalline Ice in Constitutionally Supercooled Water

Abstract: Formation of a preferred texture in the unidirectional growth of polycrystalline ice from impure melt is governed by constitutional supercooling and "fast" kinetics of solidification in directions of the basal plane. The encroachment of crystals with vertical C axis (C, grains) by the others takes place immediately by a mechanism of "fast" kinetics and/or by a lateral growth via nucleation of new basal platelets in a constitutionally supercooled melt. The first mechanism is expected to be much faster in eliminating the C, grains than the second, which explains the peculiar presence of some C, crystals at relatively large ice thicknesses.

Vermiculite lamellae as substrates for transmission electron microscopy.

Abstract: Summary Chemically exfoliated vermiculite has been investigated as a specimen-support film for electron microscope. The thinnest lamellae obtained appear to be less than 1 μg/cm2 (∼4 nm) thick, have low electron noise and show good stability in the electron beam. Their surface is smooth and hydrophilic and phase texture is low.

Structural stability and mechanical behavior of thermomechanically processed dispersion strengthened nickel alloys Final report

Abstract: Thermomechanical processing effects on crystal microstructure, texture, and high temperature strength of dispersion strengthened and free nickel-based Cr, ThO2, and W alloys

The Interaction of Long-Range Order and Deformation Processes in Cu3Au Polycrystals

Abstract: It is shown that the state of ordering in a copper-25 at.- % gold alloy does not affect the texture developed on rolling. At no stage in the rolling process were significant differences detected between materials in which different states of order had been produced. A method is introduced for investigating processes of disordering in polycrystalline samples. It allows the order parameter to be determined as a function of orientation and has led to the conclusion that hard orientations, i.e. those having a large M value, disorder less rapidly than soft orientations. This result is at first sight surprising, but can be accounted for in terms of the mechanisms of polycrystalline deformation.

Variation in the Characteristics of Deformation of Marble and Mortar Due to Transition of Stress from Isotropic State to Anisotropic State

Abstract: In the previous tests performed of cubic specimens of cement mortar, the authors showed that the material would turn anisotropic with increase of the deviatoric stress component, and that the texture of the material underwent changes with increase of its hydrostatic stress component. From these results it is supposed that cement mortar which seems to be macroscopically homogeneous and isotropic will exhibit anisotropy not by the intrinsic property of the material, but by the transition of stress in state, and that the internal change of the texture of the material depends upon the degree of porosity contained in the material.The triaxial compression tests by experiments I and II were therefore performed of cement mortar and marble specimens with considerable difference in porosity in them respectively under various states of stress, in order to investigate the relationship between the textural change and the characteristics of deformation due to the transition of stress from isotropic state to anisotropic state. From the results of these tests the authors found the following facts.(1) The internal texture of the material undergoes changes and resistance against deformation decreases with increase of hydrostatic stress under different levels of stress on mortar and marble. The characteristics of deformation tend also to be anisotropic as deviatoric stress increase.(2) The characteristics of deformation are definitely determined by the state of stress regardless of its path if the given stress of the material is below its yield stress.

Effect of isotropic surface films on the distribution of magnetic-phase concentrations in transformer steel with ribbed texture

Abstract: 1. Isotropie surface films which produce tensile stresses in their substrates (cold-rolled transformer steel) increase the concentration of the magnetic phase, the vector Js of which is in the rolling direction, while films producing compressional stresses reduce this concentration. 2. For films which are not too thick, the dependence of the ratio of magnetic-phase concentrations on the thickness of the surface film is exponential.