The development of the rolling texture of f.c.c. metals dependent on relative stacking-fault energy

Neutronographic texture investigations are presented for nickel and Co32Ni – the representatives of f.c.c. metals of very high or extremely low relative stacking-fault energies, resp., as well as for α-brasses with zinc concentrations between 1 and 4 atomic percent, which are typical for mean values of γ/Gb. The discussion of the results is based on three-dimensional distribution functions calculated by series expansion. For the main texture components a higher indexing as usually is assumed what is also due to the orientations of these minor components originating in the mechanical twinning. The origin of additional minor components of additional minor components is attributed to the formation of surface textures and recrystallization phenomena. The texture development at extreme relative stacking-fault energies is associated with cross slip or microtwinning and partial glide, resp.     

F.C.C. Rolling Texture Transitions in Relation to Constraint Relaxation

A complete set of f.c.c. rolling texture predictions, obtained with the use of a relaxed constraint model, is presented in this paper. The whole spectrum of textures between the copper and brass types can be found if some components of reaction stresses (between grains and the matrix) are relaxed. The best prediction of the copper type texture is found if ϵ₁₃ is a free parameter and the other components of grain deformation tensor are controlled by reaction stresses. The best prediction of the brass type texture is obtained if ϵ₁₂, ϵ₁₃ and ϵ₂₃ are free parameters. However, a decisive factor for the texture transition from the copper to the brass type is the relaxation of the ϵ₁₂ component. We present for all the considered cases the orientation distribution functions (O.D.F.) and also the pole figures for some selected cases. Nous présentons pour tous les cas les fonctions de distribution d'orientations cristallines ainsi que dans certains cas — les figures de pǒles.     

Rotation field and continuity equation for texture evolution

In the present paper a quite general approach is proposed for the problem of the formation of the prefered orientations (i.e. of the texture). The rotation field is considered by the present authors as the most general variable which describes completely the texture formation process. The proposed continuity equation transforms immediately the rotation field to the texture function (Orientation distribution function). The presented formatlism is illustrated by a few f.c.c. rolling textures.     

Texture of Y- and Bi-HTSC and Methods for its Determination

Investigation of the texture of Y- and Bi-HTSC materials by X-ray techniques involves certain difficulties owing to the peculiarities of their crystal structure which causes the arrangement of reflexes in dense groups and practically precludes the formation of a pole figure from an isolated reflex. The texture of Y- and Bi-HTSC materials has been investigated by constructing direct pole figures in an automatic texture diffractometer DAPT YM 1 in CuKα emission from groups of reflexes which are unresolvable under the test conditions. The choice of groups of reflexes was dictated by the type of texture formed. With a basal texture of packing of powders, the following groups have turned out to be the most suitable for the YBa₂Cu₃O_7–x phase (123): (013) + (110) + (103), 2θ = 32.3 – 32.8º and (014) + (005) + (104), 2θ = 38.5 – 38.8º. They include the reflexes which are structural and superstructural relative to a bcc subcell with a rather slight orthorhombic distortion, with its tripling along the “c” axis forming a cell of (123) compound. For the Bi₂Sr₂CaCu₂O₈ phase, there have been used the groups of reflexes (008) + (111) + (1.4/54), (0.0.10) + (1.6/5.4) + (0.9/5.1), (0.0.12) + (1.6/5.8) + (204) + (119). (115) + (1.6/5.4) + (0.1/5.9), and (117) + (0.9/5.1) + (1.6/5.6) + (1.4/5.8), 2θ with respectively 23.2 – 24.0º, 29.1 – 29.7º, 35.1 – 35.2º, 36.5 – 28.4º, and 29.7 – 31.4º. They also include reflexes from the lattice constructed by multiplication of a perovskite cell with α = 5.40 Å, b = 5.41 Å and c = 30.6 Å along the “b” axis. Y-HTSC-based materials also contain a component of shear texture which is close to such a texture in bcc metals. The texture of Y- and Bi-HTSC materials is relatively stable in hightemperature annealing. The nature of the effect of annealing at moderate temperature is different.     

HVEM Study of the Development of the Recrystallization Texture in Deformed Copper Single Crystals

〈110〉-orientated single crystals of high purity copper were deformed in tension up to 80% elongation. Sections of the deformed material were examined by HVEM before and after annealing in situ. Additional measurements by a texture goniometer confirmed and supplemented the metallographic results. The orientations of all recrystallized micrograins can be interpretated as the result of multiple annealing twinning. Since the grain boundary energy may be lowered by twinning the new orientations may be selected for this reason. These results can explain the recrystallization textures observed by X-ray techniques.     

Direction-Dependent Orientation Distribution Function of Textures and Consideration of Twin Formations. Application to Copper and Gypsum Samples

A program was created for calculating the orientation distribution function of textures for all crystal systems. The method corresponds to a superposition of pole figures. This program, which follows the WIMV procedure, is based on a direction-dependent representation in the reciprocal space. The advantage over representation with Eulerian angles is that an axial transformation is not necessary in the oblique crystal systems. Fibre textures appear in the diagrammes as one-dimensional stripes. Different components of a fibre texture can be clearly depicted in a stereographic projection. The occurrence of twins and oriented intergrowths can be determined. Results of texture determinations on copper from a plumbing system and on a polycrystalline gypsum preparation are given below.     

Cold rolling texture development in Zn,Cd and Mg

Studied are the regularities of preferred orientations in the process of rolling of zinc, magnesium, and cadmium. On the basis of the data obtained and analysis of crystallographic mechanism of Cd, Zn and Mg crystals a “dynamic” model of the rolling texture formation in zinc and cadmium as well as a “monotonic” one in magnesium are suggested.     

Crystal structure and habit of fine metal particles formed by gas-evaporation technique; bcc metals (V,Fe, Cr,Mo and W)

Fine particles of several kinds of bcc metals were prepared by evaporation in an argon atmosphere. They were collected at various growth zones in the smokes and their structures and habits were studied by electron microscopy. Vanadium and iron particles grown in all zones have the ordinary bcc structure. However, chromium and molybdenum particles grown in the inner part of the smokes have the bcc structure, and those in the outer part have the A-15 type structure. Habits of particles with the bcc structure can be generally described in terms of rhombic dodecahedra truncated by six (100) faces with various degrees of truncation from 0 to 100%. The truncated rhombic dodecahedron is a common habit to the bcc metals, though the degree of truncation is dependent on the metal. For vanadium it varies from zone to zone systematically. Molybdenum particles of rounded cube and {211} icositetrahedron are found to have the A-15 type structure in addition to the well known {211} icositetrahedron and rhombic dodecahedron found in chromium.     

Zur Struktur von organischen Mischkristallschichten

The structure of organic mixed crystal films is investigated by means of a appropriated model - copper phthalocyanine/vanadyl phthalocyanine. These films are polycrystalline and contain mixed crystal grains, the size being smaller than that which can be detected by X-ray methods. By infrared spectroscopy and scanning electron microscopy or after recrystallisation by texture goniometer investigations the orientations of microcrystals on the substrate was obtained.     

Plastic Deformation of BCC Metals — Open Problems

For a deeper understanding of the plastic behaviour of bcc metals a detailed knowledge of the mobility of screw dislocations, which is intimately connected with their core structure, is necessary. A critical review of our present knowledge indicates an almost absolute lack of quantitative information on screw dislocation mobility at finite temperatures. Therefore, a detailed experimental and theoretical study of these processes is an open problem of great importance. Such a study would be of great value for the entire field of plastic deformation of bcc metals.     

Growth of Biaxial Textured MgO‐Layers by Ion‐Beam Assisted Pulsed Laser Deposition

MgO thin films were deposited on amorphous substrates using pulsed laser deposition. Without an assisting ion beam, strong fibre textures are observed changing with temperature. Using an ion beam at 55° with respect to the substrate normal and energies of more than 400 eV, biaxially textured films are grown with the <200> direction parallel to the ion beam. Decreasing the deposition rate the texture changes towards the desired cube texture and resputtering becomes more important. Investigations of the surface topography show an increase in roughness and grain size with increasing film thickness. Preliminary ideas of texture and microstructure development in this deposition process are presented.     

Rolling Textures Predicted by the Elasto-plastic Self-consistent Model

The rotation rate fields of a f.c.c. polycrystal deformed by rolling have been predicted by the self-consistent model for different values of the plastic accomodation parameter. The isotropic as well as anisotropic hardening of slip systems have been taken into account. The obtained rotation rate fields have been applied next to the continuity equation of texture evolution. All the results may be classified into two groups: a copper type texture and a transition texture (probably towards the brass type one).     

X-ray investigations of the defect structure of aluminium after plastic deformation

With plastic deformation of polycrystalline metals deformation textures are build up. Our experimental results show that the dislocation density increases, even with small plastic deformation. Simultaneously a decrease in the value of coherence length was revealed. The formation of a distinctly marked sub-structure, which is accompanied by an increase of the dislocation density, is essentially completed when plastic strain reaches 30 per cent. Further increase of the degree of deformation is followed by a change of orientation of the subgrains. When plastic strain is 60 per cent the deformation texture is almost completely accomplished.     

Relationship between excess entropy and microstructure of undercooled liquid metals

Molecular dynamics simulations were performed for stable and undercooled liquid metals. The inherent structures formalism was used to explore the potential energy landscape, showing a competition between crystalline (fcc and bcc) and icosahedral (regular and distorted) order. The two-body approximation of the excess entropy is used to study the interplay between the microstructural ordering and the entropy of undercooled liquid metals. A strong correlation between the excess entropy and the relative changes in the crystalline and icosahedral order is obtained, indicating that entropic effects are coupled to the microstructural changes of undercooled liquid metals. Thermal entropy behavior was obtained by using structural information of both inherent structures and atomic configurations.     

On microcrack nucleation at twin vertices and boundaries in bcc and fcc metals

Nucleation of microcracks at the vertex and boundary of a decelerated twin is studied for a number of bcc and fcc metals. A twin and its boundary are represented as stepped pileups of twinning dislocations located in the neighboring glide planes. The formation of microcracks through the merging of head dislocations by the force and thermally-activated mechanisms is analyzed. Analytical expressions are obtained that describe the conditions necessary for microcrack nucleation at the vertices of stepped dislocation pileups. It is established that with an increase in the shear-modulus value, the critical parameters of microcrack nucleation by the two above mechanisms become closer in all the metals considered.     

Study of Cholesteric Textures in Phase Change Devices by Laser Light Diffraction

Photographic-recording and photomultiplier-recording laser light diffractometers have been constructed and used to study the cholesteric textures in phase change devices as a function of applied voltage and device parameters. The focal conic texture formed with increasing voltage gives diffraction peaks corresponding to 2π rotations of the director, whereas the texture formed by slow nucleation with decreasing voltage also gives “superlattice” lines corresponding to a 4π repeat, due to the different local structures of the textures combined possibly with tilting of the director. The repeat distances obtained by indexing the diffraction patterns agree well with microscopical and infra-red reflectance observations. Laser light diffraction appears to be a powerful technique for quantitative study of the non-uniform unwinding and re-forming of cholesteric twist in an electric field.     

Anwendung der „Optimalfilter-Methode”︁ bei der röntgendiffraktometrischen Bestimmung von Differenz-Elektronendichten

The method of the difference Fourier analysis with differences between measured and theoretical structure factors for the determination of covalent bonds in metals and metal alloys is described. The strategy of the measurement and the method of the evaluation are developed with the “optimum filter” for this special application, and examined at bcc alloys.     

Decomposing textures of hexagonal magnesium alloys with fiber component

The orientation distribution function (ODF) calculated from measured pole figures with series expansion method is decomposed into texture components of Gauss type distribution and the volume fraction of texture components can be calculated with the model distribution function. Firstly, as fiber texture components are often found in magnesium alloy, the series expansion coefficients for Gauss type fiber components are derived. Secondly, as the textures of magnesium is very complicated, the group decomposing method, i.e., a major component accompanied by several minor components with trivial misorientation from the major one, is proposed to ensure better fitting or decomposing results. Finally, the group decomposing method is used to calculate the texture volume fraction of two typical experimental ODFs.     

Similar quartz crystallographic textures in rocks of continental earth’s crust (by neutron diffraction data): I. Quartz textures in monomineral rocks

Quartz crystallographic textures in different rocks have been investigated by neutron diffraction. Various types of crystallographic textures of quartz-bearing mineral associations in monomineral and multiphase rocks from a representative collection of samples have been revealed and classified. Experimental investigations have been performed on special neutron texture diffractometers designed at the Frank Laboratory of Neutron Physics and mounted in the seventh channel of the IBR-2 reactor at the Joint Institute for Nuclear Research (Dubna).     

Similar quartz crystallographic textures in rocks of continental earth’s crust (by neutron diffraction data): III. Relation of quartz texture types with means and conditions of texture formation

Examples of different rocks collected in different regions of the continental earth’s crust are presented. Groups of quartz crystallographic textures of the same type are selected for these rocks. The relationship between the types of textures and the physical means and conditions of their formation is analyzed. The effect of the α-β phase transition in quartz on the texture transformations in rocks is considered.