Showing papers on "Texture (crystalline) published in 1980"

Structure and Properties of LPCVD Silicon Films

Abstract: Silicon films deposited by low pressure chemical‐vapor deposition over the temperature range from 525° to 725°C were investigated. It was found that polycrystalline films are formed above 600°C and are more stable than the amorphous films deposited at lower temperatures. Their crystal structure is a strong function of the deposition temperature and a weaker function of the deposition rate. Either the {110} or the {100} texture may dominate the structure, depending primarily on the deposition temperature. The electrical resistance obtained on doping the LPCVD films that are polycrystalline as deposited is maximum for films deposited at the lower temperatures (near 600°C), although this dependence on deposition temperature decreases after annealing at higher temperatures. Dopant atoms reversibly segregate to the grain boundaries during lower temperature heat‐treatments subsequent to doping and are dispersed at higher temperatures, with corresponding changes in resistivity. The oxidation rate is only a weak function of the deposition temperature, although the initially amorphous films may oxidize somewhat more rapidly. The index of refraction of amorphous films is significantly higher than that of polycrystalline films.

Inhomogeneity of rolling texture in fcc metals

Abstract: The cold rolling of metal sheets and strips results in the formation of an inhomogeneous texture. The type and sharpness of texture in layers and the degree of inhomogeneity depend on the friction between rolls and the material and the geometry of the rolling gap. Contrary to the opinion of several authors, it is shown that the inhomogeneity of texture appears not only in the case of small values of thel/h ratio (l/h characterizes the geometry of the rolling gap) but also in the case of large values whenl/h > 5. In the first case shear texture forms in the intermediate layers of the rolled sheet while in the second, in its outer layers. The results of experiments carried out on aluminum, silver and 70/30 brass clearly show that the sensitivity of metals and alloys to the formation of an inhomogeneous texture is caused by their flow characteristics: yield strength (Y) and the work hardening exponent (m). High values ofY andm will tend to hinder the shear deformation, and consequently they will hinder the occurrence of inhomogeneity.

Effect of Texture on Microwave Emission from Soils

Abstract: The intensity brightness temperature (TB) of the microwave emission from the soil is determined primarily by its dielectric properties. The large difference between the dielectric constant of water (?80) and that of dry soil (3-5) produces a strong dependence of the soil's dielectric constant on its moisture content. This dependence is effected by the texture of the soil because the water molecules close to the particle surface are tightly bound and do not contribute significantly to the dielectric properties. Since this surface area is a function of the particle size distribution (soil texture), being larger for clay soils with small particles, and smaller for sandy soils with larger particles; the dielectric properties will depend on soil texture. This dependence has been demonstrated by laboratory measurements of the dielectric constant for soils which are briefly summarized in this paper. The dependence of the microwave emission on texture is demonstrated by measurements of TB from an aircraft platform for a wide range of soil textures. The main conclusion of the paper is that the effect of soil texture differences on the observed TB values can be normalized by expressing the soil moisture values as a percentage of field capacity (FC) for the soil.

The Dependence of Strength‐Controlling Fracture Energy on the Flaw‐Size to Grain‐Size Ratio

Abstract: The transition from single-crystal to polycrystalline fracture energies was studied as a function of the flaw-size to grain-size ratio by two methods. The primary method was calculating fracture energies from observed flaw sizes found at fracture origins in strength-test specimens. Some measurements were also made by varying the number of grains across the web in the applied-moment DCB test. Both methods agreed and generally snowed the transition to polycrystalline fracture energies being completed at flaw-size to grain-size ratios of ∼1 to ∼ 6 for the cubic materials studied. It is estimated that cracks less than ∼½ to ¼ of the grain size cannot be arrested at grain boundaries and that single-crystal fracture energies can be applied below this limit. The grain-size range over which this fracture-energy transition occurs was shown to be a function of extrinsic factors, such as texture, as well as intrinsic factors, such as the number and multiplicity of low-energy single-crystal fracture planes.

Characterization by electron microscopy of carbon phases (intermediate turbostratic phase and graphite) in hard carbons when heat-treated under pressure

Abstract: As hard carbons are heat-treated under pressure (1 h, 5 kbar) an intermediate thermally stable carbon phase (d 00.2=3.39A, turbostratic) appears above 1100° C. Its proportion increases up to 1600 or 1700° C depending in the initial sample (saccharose or glassycarbon). The morphology of this new phase has been determined by HREM to be similar to crumpled sets of paper sheets, it is thus highly porous. When heat-treated under pressure above 1600 or 1700° C, this phase is suddenly transformed into graphite, i.e. the porous texture flattens into lamellae.

Study of crystal texture in pvc gels by x‐ray diffraction and infrared dichroism

Abstract: An enquiry is presented into the nature and origin of thermoreversible gelation of poly(vinyl chloride) (PVC). In line with a previous paper it is demonstrated by direct x-ray diffraction evidence that the origin of the gelation is crystallization, and that this crystallinity can be conspicuously apparent even for the usual technological polymer. In addition some unusual diffraction effects become apparent such as do not obviously follow from existing notions of the PVC structure. Combined infrared dichroism and x-ray studies revealed that these new effects are attributable to a two-component nature of the crystallinity where the components are distinguished by their orientation behavior, lateral extension, and possibly morphology of the crystallites. Some of the crystals orient with their a axes (type A crystals) and some with their c axes (type B crystals) along the stretch direction. Other more complex orientability differences are also manifest during film formation. Crystals B are smaller, and are believed to correspond to the network forming junctions, hence to fringed micellar crystals. Crystals A have a less evident connection with the network and are hypothesized to be of lamellar character, the behavior of which is closely simulated by lamellar crystal additives (stabilizer crystals). High-temperature x-ray work revealed no melting of crystals even in the temperature range where endotherms appear in the thermograms.

Evaluation of (residual) stresses in textured cubic metals

Abstract: In residual stress measurements with X-rays, the interplanar spacing is often assumed to alter linearly with the orientation of the reflecting grains with respect to the stress system; the calculation of the stresses is based on this assumption when either the well-known two-tilt or sin2ψ methods are employed. But in materials with strong texture, large oscillations have sometimes been reported. A method proposed in the literature for evaluating stresses in such a situation in terms of elastic anisotropy has been tested and shown to provide a reasonable stress system; however, the texture must be known in detail, so as to calculate the effective anisotropic X-ray elastic constants. More importantly, the theory predicts that well-established standard methods (and measured or calculated isotropic X-ray elastic constants)can be used, and without knowledge of the texture,if hoo andhhh reflections are employed; this has been verified experimentally in this study. It is recommended that such reflections be employed in the future, rather than the common ones now utilized.

Electromigration in fine‐line sputter‐gun Al

Abstract: The electromigration behavior of Al films, deposited by the sputter gun (varian s‐gun) and ranging in alloy content from 0.5% Cu to 2% Si has been evaluated for 2.5 cm long, 1–4 μm wide conducting stripes. An inverse square dependence of lifetime on current density has been verified. Furthermore, it has been shown that film composition affects the electromigration lifetime through its contribution to the grain structure, in that, an increase in lifetime accompanies an increase in grain size and a decrease in spread of the grain size distribution. Increasing the Si content is detrimental, since it results in a reduction in grain size. Failures occur by the random growth of subsurface voids along the conductor length. The s‐gun films have a completely random orientation in contrast to electron beam evaporated Al‐0.5% Cu, which exhibits a prominent 〈111〉 fiber texture. This preferred grain orientation in the case of the latter is held responsible for its superior lifetime in comparison to the sputtered films.

ZnO Processing for Bulk- and Surface-Wave Devices

Abstract: Zinc-oxide thin-film transducers are used in a variety of microwave acoustic device applications for the generation and detection of bulk and surfaceacoustic waves. High coupling factor-low acoustic loss films are characterized by their dense, fine-grain, well-ordered crystallite structure, optical clarity and smooth surface texture. Sputtering the films using a compound ZnO target at moderate rates, with low reactive gas pressures on heated substrates, has produced films whose piezoelectric and acoustic properties approach those of single crystal zinc oxide. Several diagnostic techniques such as XRD, RED, SEM, TEM, optical, chemical and electrical havebeen used to characterize acoustic quality. This paper will discuss process conditions that lead to high quality film growth and diagnostic measures which best predict transducer performance.

Crystal structure and thermal oxidation of laser‐recrystallized polycrystalline silicon

Abstract: Laser‐recrystallized polycrystalline silicon exhibits a weak 〈111〉 preferred orientation, in contrast to the strong 〈110〉 texture seen in fine‐grain poly‐silicon. The oxide thickness thermally grown on laser‐recrystallized poly‐silicon is much greater than that on fine–grain poly‐silicon when both are heavily phosphorus doped but is approximately the same when both films are lightly doped.

Structure of elongated and spherulitic domains in long pitch cholesterics with homeotropic boundary alignment

Abstract: 2014 Elongated and spherulitic domains, as occurring in cholesteric layers with a pitch equal to about a layer spacing, have been investigated by optical methods. Several new properties have been discovered, and three varieties of domains could be distinguished. All properties of the domains, known up to now, and the homeotropic boundary alignment have been taken into account to construct their director field. The vertical defect line in the centre of the spherulitic bubble domains has been discovered to be a metastable singularity.

Effect of soil texture on the microwave emission from soils

Abstract: The intensity brightness temperature of the microwave emission from the soil is determined primarily by its dielectric properties. The large difference between the dielectric constant of water and that of dry soil produces a strong dependence of the soil's dielectric constant on its moisture content. This dependence is effected by the texture of the soil because the water molecules close to the particle surface are tightly bound and do not contribute significantly to the dielectric properties. Since this surface area is a function of the particle size distribution (soil texture), being larger for clay soils with small particles, and smaller for sandy soils with larger particles; the dielectric properties will depend on soil texture. Laboratory measurements of the dielectric constant for soils are summarized. The dependence of the microwave emission on texture is demonstrated by measurements of brightness temperature from an aircraft platform for a wide range of soil textures. It is concluded that the effect of soil texture differences on the observed values can be normalized by expressing the soil moisture values as a percent field capacity for the soil.

The sputtering yield of polycrystalline materials

Abstract: Measurements were made of the sputtering yield of polycrystalline niobium due to 15 kev argon ion bombardment. The crystallographic orientations of individual grains were carefully surveyed using selected area electron channeling patterns. It was demonstrated that the average yield behavior could be calculated from theory provided allowance was made for ion channeling. The method for calculating yields can be applied to any combination of ion-polycrystalline target material provided the distribution of grain orientations (texture) is known.

Steam turbine rotor

Abstract: PURPOSE: To raise creep strength at high temperature and also toughness at low temperature for a steam turbine rotor by using a 12-Cr steel with a specific composition. CONSTITUTION: A steam turbine rotor is manufactured by a procedure in which a 12-Cr steel, consisting of 10W13% Cr, 0.3W1.0% Mn, 0.5W2.0% Mo, <0.2% Si, 0.1W1.5% Ni, 0.01W0.5% Nb, 0.1W0.5% V, 0.5W2.0% W, 0.05W0.3% C, and 0.01W0.3% N, is melted, deoxidated with carbon under vacuum, cast into a mold, and then heated to 1,000W1,300°C. Then, the cast ingot is completely austenized by heating it to 1,000W1,150°C, rapidly cooled in oil or by water spraying to approx. 100°C to make its texture uniform martensite structure, and tempered at 550W 700°C for a long period of time to make it a complete martensite structure where no ferrite texture is produced. Thus, a steam turbine rotor having a high creep strength at high temperatures and excellent toughness at low temperatures can be obtained. COPYRIGHT: (C)1981,JPO&Japio

Formation of α→γ→α Transformation Texture in Sheet Steel

Abstract: For the purpose of investigating the formation mechanism of the texture which is developed by ferrite (α)→austenite (γ)→ferrite (α) transformation, the effects of heating and cooling rates during phase transformation and specimen thickness on the transformation texture have been studied by using an extra low carbon sheet steel with the initial texture of {111}.The results obtained are summarized in the following:(1) A weak {100} and {111} texture was formed in the surface layer of the specimen transformed by rapid heating and rapid cooling.(2) By rapid heating and subsequent slow cooling, a texture with {110} orientations and orientations 20-30 deg shifted away from {100} was obtained in the surface layer.(3) Slow heating and slow cooling produced a distinct {100} texture in the surface layer.(4) There was a marked difference in texture between surface and midsection of thick specimen: In the midsection, the texture similar to that described in (1) was formed, independent of the heating and cooling rates. While, the specimen surface exhibited the texture as mentioned in (1) to (3) on each condition.(5) Those results were consistently explained on the assumptions that the orientation relationship between bcc and fcc follows the Kurdjumov-Sachs relation, and that during a slow progress of α→γ→α transformation the orientation change proceeds preferentially by operation of such variants that generate a larger elastic work in the normal direction of a sheet surface.

Texture and its influence on the mechanical and ballistic properties of steel armor plates

Abstract: By appropriate thermomechanical processing treatment in the austenite region of a medium carbon 5Ni steel, three different types of textures, each with various degrees of intensity, have been produced in the quenched-and-tempered high-hardness steel armor plates. The various mechanical properties, including tension, through-thickness tension and compression, impact, fatigue, and fracture toughness, together with the ballistic performance of the plates as a function of the intensity of the texture, in particular the (112)+(111) type, are presented and discussed.