Showing papers on "Texture (crystalline) published in 1968"

The Microstructure and Crystallography of Aluminium-Silicon Eutectic Alloys

Abstract: Aluminium-silicon alloys in the composition range 12 to 16 wt.% silicon have been frozen unidirectionally over a range of rates from ca . 0.3 to 30 μ m/s and with imposed temperature gradients ranging from 0.35 to ca . 40°C/mm. The detailed morphology and crystallography of silicon in these alloys are described and the various structures are rationalized in terms of the variables, composition, freezing rate and temperature gradient. Three growth processes are distinguished in which (A) massive silicon crystals grow at a planar aluminium front by a relatively long range diffusion process; (B) short range dif­fusion occurs at the growth front between silicon crystals which develop a preferred fibre texture; and (C) silicon crystals are more or less heavily twinned and grow by steady or fluctuating short-range diffusion processes. There do not appear to be any preferred epitaxial orientations between the phases. Similarities are noted between the microstructures of eutectic alloys in the systems Al-Si and Ag-Si, and it is shown that in chilled or ‘modified’ alloys the silicon occurs in an irregular fibrous form rather than as isolated globules. The mechanisms are discussed for (I) the growth kinetics of silicon, (II) the transition from a long-range to a short-range diffusion process, (III) steady-state, and (IV) non-steady-state growth processes, and (V) repeated nucleation of silicon crystals from the liquid.

Shape‐Memory Effect and the Martensitic Transformation of TiNi

Abstract: The object of this investigation is to provide an explanation of the shape‐memory effect in TiNi with an equiatomic composition. After a plastic deformation at room temperature of a wire or plate of TiNi, this material appears to remember its undeformed shape when it is heated above 90°C. It is well accepted that a reversible martensitic transformation takes place below 90°C. At room temperature this transformation is not completed but can proceed by mechanical stress. It is assumed that the plastic deformation at room temperature is realized by martensitic transformation. This transformation takes place in a preferred orientation which depends on the direction and the sign of mechanical stress. On heating, the oriented low‐temperature phase retransforms to the original structure and annihilates the plastic deformation. X‐ray texture measurements of reflections of the low‐temperature phase have shown the existence of a relation between an applied stress and the texture. The results have shown a marked difference in texture of martensite formed by tension and martensite formed by compression. Although the crystal structure of the low‐temperature phase is unknown, these results give an explanation of the memory effect and any proposed crystal structure or orientation relation should fulfill the relations between stress and texture.

Texture, growth and orientation of anodically formed silver oxides

Abstract: The structure, topography and growth of silver oxide deposits formed under galvanostatic and potentiostatic conditions in potassium hydroxide solutions has been studied by X-ray and electron diffraction and by electron microscopy. The argentous oxide deposit cannot be classified as being either continuous or discontinuous, but has features associated with both types of film. A random deposit is formed initially followed by the development of one-degree orientation. The argentous oxide film has a marked {111} orientation and a proportion of {112} orientation parallel to the electrode surface. Orientated argentic oxide deposits were not found under any conditions.

Chemical Deposition of Mo on Si

Abstract: A good Schottky diode has been obtained by the chemical deposition of Mo on Si. Thermodynamical consideration denotes that the deposition rate of Mo is determined by solid MoCl3 produced as the intermediate product of H2 reduction of MoCl5. If the deposition temperature is above 600°C theoretical deposition rates agree with experimental results. Mo deposited on Si at 500~800°C has the structure of fiber texture oriented to (100). Above 900°C, MoSi2 is detected by electron diffraction analysis. Between 600 and 800°C, the Mo film of thickness 1000 A has the resistivity which is very close to its bulk resistivity. By the deposition for 30 min. at 560°C, a good Mo-Si Schottky diode with the same barrier height as previously reported, is obtained. At 600°C, the deposition time must be within 15 min. to get a good Schottky diode. But the barrier height is about 20% higher than that of a diode, fabricated at 560°C.

The Growth of Oxide on Field-Ion Specimens of Iridium

Abstract: The ability of the field-ion microscope to obtain images, with atomic resolution, of a compound—iridium oxide—is proved and applied to a study of the oxidation of previously examined field-ion specimens Field evaporation of the oxide layers allows the observation of the metal-oxide interface and also the three-dimensional structure of the oxide layer From considerations of image contrast it is deduced that only the iridium ions in the oxide are imaged, but the oxygen ions do contribute to the image by modifying the nature of image points obtained from neighbouring iridium ions The oxide films examined were always polycrystalline and the nature of grain boundaries in the oxide and the extent of overgrowth deduced The original stages of oxidation were studied and it is concluded that nucleation occurs at particular crystallographic facets of the original tip (probably {102}) The texture of the oxide layer is seen to depend on the rate of increase of temperature

A transmission electron microscope study of the structure of electrolytic nickel

Abstract: In conclusion, during the electrolysis of nickel from acid sulphate solutions, the coverage of the cathode by a possible colloidal film of nickel hydroxide is the decisive factor. In its presence, the cathode exhibits a very fine-grained, randomly oriented structure. If the film is removed, the structure consists at these current densities of relatively large grains with a very strong texture [100] perpendicular to cathode. The large grains are often twinned, but no individual stacking faults are found. The inhibitive action of the hydroxide film can be eliminated by chloride ions [2], or it can be replaced by an organic additive [3].

Magnetic Properties and Texture of an Ordered Pt–Co Single Crystal

Abstract: A study of the magnetic properties of a completely ordered Pt–Co single crystal indicates that, out of the three possible sets of crystallites, one has a population twice as large as each of the two othersThis result can easily be interpreted in terms of a model of the distribution of the ordered crystallites leading to minimum strain energy This model is presented and its experimental verification through x‐ray and metallographic examination discussed

Method of rolling titanium alloys

Abstract: A METHOD FOR ENHANCING THE STRENGTH TO DENSITY RATIO OF ALPHA-BETA TYPE TITANIUM ALLOYS. THE INCREASED STRENGTH DEMONSTRATED BY THE ALLOYS OF THIS INVENTION IS ACHIEVED BY FAVORABLY ALTERING THE CRYSTALLOGRAPHIC TEXTURE OF HE ALLOY. THE ALLOY TO BE TEXTURED IS HOT ROLLED IN AT LEAST THREE DIFFERENT ORIENTATIONS AT A TEMPERATURE WITHIN A RANGE OF FROM ABOUT 700* TO 1500*F. THIS RESULTS IN A REDUCTION IN THE CROSS-SECTIONAL AREA OF THE ALLOY BY ABOUT 60 TO 90%.

Microheterogeneity of Glassy Films of As2Sx (x<3) and Dendritic Texture on the Glasses

Abstract: Glassy films of As2Sx with a continuous and optically uniform structure have been prepared by evaporation under the normal pressure in N2 gas, x ranging from 2.7 to 2.9. The microheterogeneity and a dendritic texture of the films have been studied by means of optical microscope, X-ray diffraction, electron microscope and chemical etching. X-ray powder data for the dendritic texture did not fit any compound listed in the A.S.T.M. data file but are essentially identical with the synthesized As2S2 (or As4S4). Electron micrographs of surfaces etched with NaOH solution indicated the microheterogeneity of the glassy films. The present results suggest that the glass film is a microheterogeneous system consisting of an aggregate mixture of As2S3 and As2S2 (or As4S4).

Texture strengthening and fracture toughness of titanium alloy sheet at room and cryogenic temperatures.

Abstract: Texture strengthening and fracture toughness of titanium alloy sheets biaxial stress fields at room and cryogenic temperatures

Crystallite Orientation Distribution in Biaxially Oriented Polyethylene

Abstract: The procedure of Roe for describing the crystallite orientation in polycrystalline samples having general texture is tested using two samples of biaxially drawn polyethylene. An automated four‐circle diffractometer was used to obtain 12 pole figures (4332 fixed points) for the film having stretching ratios 3.0 × 2.0, and 13 pole figures (4693 fixed points) for the film having stretching ratios 1.7 × 1.6. The selection of measurement geometry, procedures for data reduction and correction, and methods for computer calculation of the crystallite orientation distribution are described. While the best representation of the crystallite orientation distribution was obtained from the series of generalized associated Legendre polynomials by retaining terms through l = 12, the characteristic features of the distribution are already evident when the series is truncated at l = 6. Thus, for materials belonging to the orthorhombic crystal class, as few as four or five pole figures suffice to determine the principal fea...

A review of texture strengthening of titanium alloys

Abstract: That a crystallographic texture may be present in sheet has been known for many years. Since strong texture leads to pronounced anisotropy in strain, it is usually considered undesirable when heavy forming operations such as warm rolling must be performed. Occasionally, texture is introduced deliberately as in silicon iron for transformers. In recent years, it has been demonstrated that a strong basal-plane sheet texture can be very desirable in titanium alloys when the sheet is loaded in biaxial tension. Some of

The structure of, and the contact potential difference between, polycrystalline tungsten foil and vapour-deposited films of tungsten on glass

Abstract: X-ray techniques have been used to study the structure both of vacuum-evaporated films of tungsten on glass and of polycrystalline tungsten foil following extended heat treatment in an ultra-high vacuum. A previous prediction that the contact potential difference between the two surfaces should be zero has been checked experimentally and found to be correct. The agreement is probably fortuitous however, in view of the structural differences between the evaporated films and the polycrystalline foil. The former have a completely random orientation, while in most cases the latter show a (100) texture.

Magneto‐optic and Magnetic Properties of NdCo5, Nd2Co17, and Co Films

Abstract: NdCo5, Nd2Co17, and Co films have been prepared by vapor deposition in ultrahigh vacuum using the alternate layer deposition technique. The substrates were held at −116°C during deposition. A subsequent heat treatment caused a diffusion of the layers and formed the intermetallic compounds. Direct‐current Kerr hysteresis loops were plotted during the anneal. The coercive force was measured as a function of temperature to determine when the diffusion was completed. It was found that the films had to be heated above 600°C to form the compounds. At 25°C all films exhibited large coercive forces of 535, 270, and 210 Oe for NdCo5, Nd2Co17, and Co, respectively, but Hc decreased rapidly with increasing temperature. X‐ray analysis indicated that all films had a strong fiber texture with the c axis normal to the film. It is assumed that isotropic planar stress and a perpendicular anisotropy cause the high coercive forces at lower temperatures. For all films the optical constants n, k, and the Voigt parameters Q0 a...

Thermal expansion of molybdenum-copper and tungsten-copper pseudo-alloys

Abstract: 1. A study was made of the influence of concentration and temperature on the thermal expansion of W-Cu and Mo-Cu pseudo-alloys obtained by liquid-phase sintering. It has been found that these two systems may constitute a basis for the development of materials having predetermined thermal-expansion characteristics, with coefficients of thermal expansion ranging from 60 × 10−7 to 140−160 × 10−7 1/°C. 2. For temperature ranges between room temperature and 873°K, the concentration dependence of the coefficient of thermal expansion is satisfactorily described by an expression derived for the coefficient of thermal expansion of a two-layer sphere in the elastic state as a function of the volume fraction of the layers, but deviates substantially from the relationship proposed by Turner and Kingery [9, 10] for statistical mixtures. 3. At high temperatures, the coefficient of thermal expansion is found to exhibit a significant increase for alloys rich in the soft phase and a decrease for alloys rich in the refractory phase. This may be attributed to the low resistance to plastic deformation of the soft phase and to the influence of the refractory-phase skeleton. 4. It has been established that the coefficient of thermal expansion of two-phase W-Cu and Mo-Cu pseudo-alloys depends on texture. The thermal expansion of these materials, whose irreversible changes are linked with variation in residual porosity, has been found to exhibit hysteresis.

Matrix-microfibril texture in alpha-keratin as observed by x-ray diffraction and electron microscopy.

Abstract: THIN sections of keratin fibres can be “stained” by reaction with solutions of the salts of some heavy metals, notably silver and osmium. Electron microscopy shows a texture caused by the heavier staining of the matrix material surrounding the microfibrils. Such treatments also effectively enhance the small-angle equatorial X-ray diffraction, which has the character of the scattering from an assembly of roughly cylindrical holes (the microfibrils) in a continuous matrix of comparatively large electron density. It consists of peaks, E1, E2, E3, with equivalent Bragg spacings d1 = 80 A, d2 = 42 A, and d3 = 27 A, of which the first may be chiefly ascribed to inter-microfibrillar interference effects, and the other two to the first two diffraction fringes from a single microfibrillar hole1. The intensity ratio I2/I3 of E2 to E3 should in theory be approximately 4.2 : 1, and this agrees well with the observed value in the most studied case of silver staining2.

Silicon steels containing selenium

Abstract: DESCRIBED IS GRAIN ORIENTED SILICON STEEL HAVING A PREDOMINANTLY (110) (001) TEXTURE AND CRITICAL CARBON, MANGANESE AND SELENIUM QUANTITIES, I.E., 0.02% TO 0.07% CARBON, AT LEAST 0.045% MANGANESE 0.01% TO 0.1% SELENIUM AND NOT MORE THAN RESIDUAL SULFUR.

The analysis of epitaxic growth layers of silicon carbide by X-ray diffraction topography

Abstract: The use of X-ray diffraction topography to identify domains of different polytype in crystals of silicon carbide has been described in a previous paper. Further methods have been developed and applied to the analysis of thin films deposited epitaxically from the vapour phase onto basal surfaces of crystals of hexagonal α-SiC. The epitaxic films consist either of α-SiC, or of the cubic form β-SiC, with multiple twinning about the axis normal to the surface. The fine scale texture of interlocking twin domains is readily demonstrated in X-ray diffraction topographs.

Blow-molding apparatus

Abstract: A flexible one-piece liner of elastomer material insertable in a blow-molding cavity, the internal surface of the liner conforming to the shape and texture of the article to be blow molded. After molding, the liner is deformed sufficiently to permit the molded article to be separated therefrom.

Sheet tensile properties of titanium alloys as affected by texture

Abstract: : A study was carried out on the effect of specimen orientation on the sheet tensile properties of several titanium alloys. For these alloys, chemical analysis, microstructure, X-ray pole figures, and sheet tensile properties were determined at 10-degree increments from the rolling to the transverse direction. In addition to the conventional yield strength, tensile strength, and elongation values, strain gages were used to determine Young's modulus and Poisson's ratio. A study of plastic anisotropy was also made. It is shown that several types of textures exist in these alloys and the characteristics of the mechanical properties are anisotropic and related to the texture type. A simple approximation of the anisotropic behavior patterns can be understood by relating these patterns to single-crystal properties.

Hall-effect studies in zinc-base alloys

Abstract: Hall-effect measurements have been performed on polycrystalline samples of dilute alloys of Zn-Cu, Zn-Ag and Zn-Al Pole figure determinations indicate that effects due to texture changes on alloying are insignificant The Hall coefficient varies with the average number of valence electrons per atom, n, in a manner qualitatively similar to that reported for noble metal alloys: there is a cusp at the pure metal composition (n=2) and maxima for n<2 However, unlike the noble metal alloys, the positions of the maxima do not correlate with the compositions at which the impurity scattering becomes equal to the phonon scattering