Showing papers on "Texture (crystalline) published in 1992"

Crystallographic texture evolution in bulk deformation processing of FCC metals

Abstract: A Taylor-type polycrystalline model, together with a new fully-implicit time-integration scheme has been developed and implemented in a finite element program to simulate the evolution of crystallographic texture during bulk deformation processing of face centered cubic metals deforming by crystallographic slip. The constitutive equations include a new equation for the evolution of slip system deformation resistance which leads to macroscopic strain hardening behavior that is in good accord with experiments performed on OFHC copper. The good predictive capabilities of the constitutive equations and the time-integration procedure for simulating the stress-strain behavior and the evolution of texture under both homogeneous and non-homogeneous deformation conditions are demonstrated by comparing numerical simulations against experimental measurements in simple shear and a simple plane-strain forging experiment on copper.

Laser deposition of biaxially textured yttria‐stabilized zirconia buffer layers on polycrystalline metallic alloys for high critical current Y‐Ba‐Cu‐O thin films

Abstract: Pulsed laser deposition of yttria‐stabilized zirconia (YSZ) layers on polycrystalline metallic alloy substrates is used to produce an intermediate layer for YBa2Cu3O7−δ (YBCO) thin‐film growth. The desired (001) YSZ texture is obtained at 1.0 mTorr oxygen pressure and 70 °C. Significant improvement in (001) texturing is demonstrated by using an ion beam to assist growth. Argon‐ion‐assisted growth produces layers with alignment of the in‐plane crystal axes in addition to the (001)‐normal texture. Highly c‐axis‐oriented biaxially aligned YBCO thin films can be deposited on these layers, with Tc(R=0)=92 K and Jc (77 K, B=0 T)=6×105 A/cm2 and Jc (77 K, 0.4 T)=8×104 A/cm2. With further improvement of the YSZ texture, the YBCO current‐carrying capacity of films on polycrystalline metallic alloys may approach that of films on single‐crystal substrates.

Evolution of the crystalline texture of high-density polyethylene during uniaxial compression

Abstract: The formation of an axially aymmetrical texture in HDPE was studied through unixial compression at room temperature. The orientation of crystallographic axes was probed at various stages of the deformation process, up to an equivalent strain of 1.86, by means of WAXS pole figures. Additionally the lamellar orientation was studied using SAXS and TEM. The results of these structural and morphological studies demonstrated that the major deformation mechanism involved in plastic deformation of the crystalline phase were (100)[001] chain slip

Stress Determination in Textured Thin Films Using X-Ray Diffraction

Abstract: Thin film stresses are important in many areas of technology. In the semiconductor industry, metal interconnects are prone to stress voiding and hillock formation. Stresses in passivation layers can lead to excessive substrate curvature which can cause alignment difficulty in subsequent lithographic processing. In other thin film applications, stresses can cause peeling from mechanical failure at the film-substrate interface. Beyond these issues of reliability, stress and the resulting strain can be used to tune the properties of thin film materials. For instance, strain, coupled with the magnetostrictive effect, can be utilized to induce the preferred magnetization direction. Also, epitaxial strains can be used to adjust the bandgap of semiconductors. Finally, the anomalous mechanical properties of multilayered materials are thought to be partially due to the extreme strain states in the constituents of these materials. To fully optimize thin film performance, a fundamental understanding of the causes and effects of thin film stress is needed. These studies in turn rely on detailed characterization of the stress and strain state of thin films.X-ray diffraction and the elastic response of materials provide a powerful method for determining stresses. Stresses alter the spacing of crystallographic planes in crystals by amounts easily measured by x-ray diffraction. Each set of crystal planes can act as an in-situ strain gauge, which can be probed by x-ray diffraction in the appropriate geometry. Hence it is not surprising that x-ray diffraction is one of the most widely used techniques for determining stress and strain in materials. (For reviews of this topic, see References 5–7.) This article is a tutorial on the use of x-ray diffraction to extract the stress state and the unstrained lattice parameter from thin films. We present a handbook of useful results that can be widely applied and should be mastered by anyone seriously interested in stresses in crystalline thin films with a crystallographic growth texture.

Crystallization of silicon in aluminium/amorphous-silicon multilayers

Abstract: The crystallization of amorphous Si (a-Si) in Al/a-Si multilayer thin films has been investigated by ex situ and in situ transmission electron microscopy (TEM), X-ray diffraction and calorimetry. The a-Si crystallizes at about 200°C, a significantly lower temperature than for the pure elemental state, with a heat of crystallization of about 12 kJ (mol Si)−1. We show that crystalline Si (c-Si) nucleates within the Al layers and penetrates the Al as the c-Si grows. The speed of the growth of c-Si observed by in situ TEM was a few angstroms per second at 220°C. Al grains are separated and the layered structure is destroyed, while the Al(111) film texture is enhanced. The overall activation energy of the reaction, determined by calorimetry, is 1·2 ± 01 eV. We propose a model in which diffusion of Si through the Al grains and rearrangement of the Al grains occur simultaneously.

Structure and Low-temperature Thermal-conductivity of Pyrolytic Boron-nitride

Abstract: The microstructure and morphology of three samples of pyrolytic boron nitride deposited at different temperatures have been characterized with use of x-ray diffraction and thermal-conductivity measurements. The x-ray analysis allowed the determination of the mean interlayer spacing, the out-of-plane coherence length, and the crystallites preferred orientation. It revealed the presence of three distinct morphologies. The thermal conductivity was measured as a function of temperature in the range 1. 5 < T < 300 K. The temperature variations of the thermal conductivity were fitted by using a model previously developed for the analysis of the thermal conductivity of graphites and carbons. This fit allowed the determination of the in-plane coherence length. It also allowed the analysis of point-defect concentration and of the interlayer shear modulus. It is shown that low-temperature thermal-conductivity measurements may be used to complement x-ray diffraction data for the microstructural characterization of materials.

Texture in Rietveld refinement

Abstract: A texture model suitable for use in Rietveld-refinement programs is proposed. It is based on the series expansion of the pole distribution function in symmetrized harmonics. The model was tested on a textured plate sample of Al2O3.

Evaporated CoPt alloy films with strong perpendicular magnetic anisotropy

Abstract: CoPt alloy films with large perpendicular magnetic anisotropy, perpendicular coercivity, and saturated perpendicular remanence are reported. These films were fabricated by e‐beam evaporation at substrate temperatures near 200 °C and above. Well‐(111)‐textured Pt underlayers are shown to dramatically increase the perpendicular magnetic anisotropy of CoPt alloy films. The large perpendicular magnetic anisotropy is shown to be strongly related to good CoPt(111) texture, and not to the ordered tetragonal Co50Pt50 phase.

Texture and Anisotropy in Silicon Nitride

Abstract: In this investigation quantitative texture analysis, including calculation of the orientation distribution function, is used to demonstrate the degree of preferred orientation in β-Si3N4 which has been hot-pressed or hot-worked. The results indicate that plane strain compression can produce strong textures. The texture is decided by the processing parameters including temperature, sintering additives, and stress state. Grain rotation and preferred grain growth apparently both contribute to texture development in β-Si3N4. Basal (00l) pole figures obtained from the orientation distribution function are consistent with microstructural observations and are reflected in indentation fracture toughness anisotropy. In plane strain the ratio of maximum to minimum fracture toughness is greater than 2.

The origin of crystallographic texture produced during hot deformation in rapidly-quenched NdFeB permanent magnets

Abstract: The authors present a model for the development of crystallographic texture by hot deformation in NdFeB magnets produced by rapid solidification Favourably oriented grains, with their c-axis parallel to the compression axis, grow by mass transport through a Nd-rich liquid grain boundary phase, forming large platelet grains The driving force is the elastic energy difference between grains with c-axes making different angles with the compression axis Numerical calculations based on the known properties and conditions of these materials are consistent with a liquid diffusion model >

Deposition and analysis of lithium niobate and other lithium niobium oxides by rf magnetron sputtering

Abstract: The deposition of thin films of lithium niobate (LiNbO3) on silicon with rf magnetron sputtering has been investigated. A matrix of experiments was designed to determine the effect of several parameters on the resulting film quality. Under optimized conditions, oriented polycrystalline films of LiNbO3 are produced that exhibit a columnar grain structure with the polar axis normal to the substrate surface. Deviations from sputtering parameters optimized for producing LiNbO3, have been shown to produce films of varying proportions of either LiNb3O8 or Li3NbO4 with LiNbO3. The stoichiometry, microstructure, and electrical properties of selected films have been investigated with Rutherford backscattering, diffractometry, transmission electron microscopy, and a variety of electrical measurement techniques.

Synthesis of diamond/β‐SiC composite films by microwave plasma assisted chemical vapor deposition

Abstract: A new kind of microcrystalline composite films consisting of diamond and cubic silicon carbide (β‐SiC) has been synthesized in a microwave plasma assisted chemical vapor deposition process (MWCVD), using a gas mixture of hydrogen, methane, and tetramethylsilane. Single crystalline (111) silicon wafers and polycrystalline tungsten carbide, which were treated with diamond paste before the deposition, were used as substrates. Scanning electron microscopy, electron probe microanalysis, infrared absorption, Raman scattering, and x‐ray diffraction analysis were performed to characterize the film quality and the crystallographic structure. The results show that the film structure and the volume fractions of diamond and β‐SiC components depend mainly on the reactive gas concentrations and on the diamond nucleation density. By adjusting the reactive gas concentration, the volume fraction of the components can be varied over the film thickness. In addition, the growth texture of the diamond phases can be influenced...

Deposition of aluminum-doped zinc oxide thin films by spray pyrolysis

Abstract: Aluminum-doped zinc oxide films were prepared on Corning 7059 by an inexpensive spray pyrolysis technique. Variation in structural, electrical and optical properties with doping concentration is investigated in detail. The films were highly transparent to the visible radiation and electrically conductive. X-ray diffraction results show that all films were polycrystalline in nature with [002] preferred orientation. Texture coefficient and grain size were calculated along the [002] direction for all films with different doping concentrations. Carrier concentration and mobility values were determined by measuring the Hall voltage at room temperature. Good correlation between structural and electrical properties was found.

Growth mechanisms and properties of 90 degrees grain boundaries in YBa2Cu3O7 thin films.

Abstract: The transport properties of three types of 90 o grain boundaries of (103) oriented YBa 2 Cu 3 O 7 (YBCO) thin films grown epitaxially on (101) SrTiO 3 and (101) LaAlO 3 substrates in situ by 90 o off-axis sputtering are compared. A simple description of the in-plane crystallographic film orientation is given by substrate [010]∥YBCO[010] and substrate [101]∥YBCO . A domain structure exists with the CuO 2 planes oriented at ±45 o to the substrate surface (i.e., parallel to the substrate [010] direction)

Role of Overpotential on Texture, Morphology and Ductility of Electrodeposited Copper Foils for Printed Circuit Board Applications

Abstract: A study was made to correlate different electrodeposition parameters, like, e.g., cathodic overpotential, bath composition, and bath ageing, with characteristics as crystallographic texture and roughness, and the ductility of electrolytic copper foils. Copper foils with a low (220) preferred crystallographic orientation, and a smooth surface are obtained when depositing at 87 to 113 mV cathodic overpotential from copper sulfate solutions with a low chloride content. Under these plating conditions copper foils with the highest ductility were achieved

Microstructural dependence of magnetic properties of Pt/Co multilayer thin films

Abstract: The magnetic properties of thin film Pt/Co multilayers with perpendicular magnetic anisotropy depend on their preparation. Vapor‐deposited and Xe‐sputtered multilayers have the largest anisotropy energy and coercivities, attractive for magneto‐optical recording media. Films sputtered with a smaller mass gas (Ar) have less attractive magnetic properties. In this paper it is shown by high resolution electron microscopy that microstructural differences, related to the energetics of the deposition process, caused the differences in magnetic properties. Films prepared by Ar‐sputtering experienced energetic bombardment by reflected Ar neutrals and consequently had smooth, continuous Co and Pt layers, but only modest (111) fcc texture. Vapor‐deposited and Xe‐sputtered films, which experienced much less energetic bombardment, had superior (111) texture and sharp column boundaries, although Co–Pt layer interfaces were rougher. It was concluded that the superior (111) fcc texture was responsible for a large magneti...

Characterization of low thermal conductivity PAN-based carbon fibers. [PolyAcryloNitrile]

Abstract: The microstructure and surface chemistry of eight low thermal conductivity (LTC) PAN-based carbon fibers were determined and compared with PAN-based fibers heat treated to higher temperatures. Based on wide-angle x ray diffraction, the LTC PAN fibers all appear to have a similar turbostratic structure with large 002 d-spacings, small crystallite sizes, and moderate preferred orientation. Limited small-angle x ray scattering (SAXS) results indicate that, with the exception of LTC fibers made by BASF, the LTC fibers do not have well developed pores. Transmission electron microscopy shows that the texture of the two LTC PAN-based fibers studied (Amoco T350/23X and /25X) consists of multiple sets of parallel, wavy, bent layers that interweave with each other forming a complex three dimensional network oriented randomly around the fiber axis. X ray photoelectron spectroscopy (XPS) analysis finds correlations between heat treated temperatures and the surface composition chemistry of the carbon fiber samples.

Mechanical properties and texture of dense polycrystalline Bi2Sr2CaCu2Ox

Abstract: Very dense Bi2Sr2CaCu2Ox bulk specimens were fabricated by hot isostatic pressing or sinter forging. The specimens exhibited textures in which the c-axes were aligned preferentially perpendicular to the top and bottom faces. Fracture toughness was found to be dependent on orientation, with the values ranging from 2.7 to 3.9 MPa m0.5. The average Vickers hardness for the specimens was approximately=700 MPa. Elastic anisotropy determined by velocity of sound measurements was consistent with textures determined by X-ray diffraction.

Rolling textures of a Cu/1b20%Nb composite

Abstract: Heavily rolled in-situ MMCs of Cu-20 vol% Nb have been investigated by means of quantitative texture analysis mainly for three reasons. First, the crystallographic texture can be very sensitive to the deformation process. Second, the orientation distribution affects the strength of the material in terms of the Taylor factor. Third, the influence of a massive second phase on texture development is of general interest for texture evolution of in-situ processed composites. The textures of both phases in the MMC were compared to those of single phase Cu and Nb, respectively. The results were interpreted by means of Relaxed Constraints Taylor Theory. INTRODUCTION AND EXPERIMENTAL Cu and Nb have neglectable mutual solubility. Ribbon reinforced in-situ MMCs can thus be processed by large degrees of deformation. The deformed Cu-20 vol% Nb composite reveals a tensile strength which exceeds the value predicted by the rule of mixtures. Various models have been proposed to explain the observed strength anomaly. The barrier model by Spitzig et al. (1) attributes the strength to the difficulty of propagating plastic flow through the fcc-bcc interfaces while the group of Courtney et al (2) interprets the strength in terms of geometrically necessary dislocations owing to the incompatibility of plastic deformation of the bcc and fcc phase. Both models are able to describe the increase of strength by assumption of fitting parameters, although the actual strengthening processes are still unknown. The cast Cu-20 vol% Nb composite was rolled to e=88%, 96%, 97%, 99% and 99.5% deformation. Incomplete X-ray pole figures were measured from 5" to 85" in the back reflection mode. From a set of four pole figures ({I l l ) , (2001, (2201, (311) for Cu and { I 101, (2001, (1121, (103) for Nb) the orientation distribution function (ODF) was calculated using the series expansion method (3). For correction of "ghost" errors the calculated ODFs were approximated by model ODFs (4). RESULTS AND DISCUSSION The rolling texture evolution of Cu in the composite (Fig.1) is very similar to the texture development of pure Cu (Fig. 2) (S), except for two details. At very large deformation (E= 99.5%) the C orientation {112} decreases from 16 vol% to 10 vol%, whereas the background rises from 20 vol% to 26 Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:19937271 1728 JOURNAL DE PHYSIQUE IV vol%. In pure Cu the C component typically decreases at very large deformation, while its twin of first generation increases and the background decreases (Fig.2a). The increase of the twin is however not observed in the composite. Moreover, small amounts of {001) , which is a recrystallization component in copper (6) appear, although not systematically with increasing deformation (Fig.lb). We interpret this phenomenon as a result of dynamic recrystallization. In case of static recrystallization the cube or the {025} orientation should increase continuously with increasing deformation (Fig.2b). This is at variance with the measurements. Since {001) is unstable upon rolling, it rotates away with increasing degree of deformation, so that no steady increase of {001) can take place during deformation. The decrease of the C orientation (Figla), combined with the increase of the background at ~=99.5% can then be attributed to the formation of cube nuclei from the C orientation, because from static recrystallization experiments i t is known that the cube orientation nucleates preferentially in the C component (6). The newly formed orientations with volume fractions below 2-3% enrich the background only. This interpretation would also explain the low dislocation density in the Cu phase of the composite (I). The texture of the Nb phase in the composite is characterized by a sharp bcc-a-fibre (Fig.3a) and the absence of {111} component and thus corresponds to the measurements of pure Nb (Fig.%). In single phase material a significant shear ~ 2 3 cannot be allowed without generating severe incompatibility problems between adjacent grains. In a composite, however, the Nb ribbons are embedded in a softer, maybe even recrystallized Cu matrix, which mitigates the incompatibility created by a shear ~ 2 3 in the Nb (Fig.6). Allowing for E23#0 during rolling suppresses the development of the {111) component (Fig.4~) in agreement with the Nb texture in the composite (Fig.3b). This means that in the composite the constraints for Nb become anisotropic, allowing a stronger ~ 2 3 shear of Nb into the Cu phase but hinders its ~ 1 3 shear.

Effect of Initial Orientation on the Cold Rolling Behavior of Solidified Columnar Crystals in a 19% Cr Ferritic Stainless Steel

Abstract: The cold rolling behavior of solidified columnar crystals in a 19% Cr ferritic stainless steel has been investigated in order to clarify the effects of the initial orientation of each columnar grain and of the interaction with adjacent grain in a polycrystalline specimen. The specimen showed {001} texture before rolling and {001} texture after 70% rolling reduction. It was clearly shown that the rolled microstructure and the crystal rotation by rolling strongly depend on the initial orientation. The 70% rolled microstructure of (001)[100] oriented grains consisted of a large number of fine stringer deformation bands, whereas (001)[110] oriented grains showed a uniform and non-characteristic deformation structure. In the grains having intermediate orientations such as (001)[510]-[320], stringer deformation bands formed near grain boundaries. Both of the (001)[100] and (001)[110] oriented grains maintained their initial orientations even after 70% rolling reduction, while the (001)[510]-[320] oriented grains rotated toward (001)[110]. It was emphasized that the stability of (001)[100] orineted grains against rolling is contrast to the case of (001)[100] oriented bcc single crystals where the crystal rotation toward (001) occurs. This difference was discussed from a viewpoint of the interaction with adjacent grains.