Materials Science Forum Vols. 495-497

Abstract: YBa2Cu3O7-δ (YBCO) films were deposited on (100), (110) and (111) oriented silver single crystals and {100}<100>, {110}<211> , {110}<100>+{110}<011>， {110}<011> and {012}<100> textured Ag substrates using pulsed laser deposition. The relationship between the epitaxial growth YBCO film and silver substrate has been determined. It is shown that among polycrystalline Ag substrates, {110}<011> textured tape is suitable for the deposition of YBCO thin films having strong texture.

Abstract: In this study, a hot forging process is applied to Nd-Fe-V as cast alloys in order to develop both the microstructure and the crystallographic texture appropriate for permanent magnet properties. A neutron diffraction texture analysis is used to account for the extrinsic magnetic anisotropy: the stabilisation of the Nd(Fe,V)12 hard magnetic phase has been achieved during forging but its extrinsic anisotropy level remains low. Attempts to understand this phenomenon are made through a discussion on the Nd-Fe-V alloy rheological and mechanical behaviour and a comparison with Nd-Fe-B permanent magnets.

Abstract: The orientation distributions of α-Al2O3 textured ceramics are determined from neutron diffraction and SEM-EBSD. A curved position-sensitive detector coupled to a tilt angle (χ) scan allowed the whole neutron diffraction pattern treatment in the combined Rietveld-WIMV-Popa algorithm. Analyses from neutron and electron diffraction data gave similar results if EBSD data are smoothed to account for grain statistics. Four textured alumina ceramics were prepared by slipcasting under a high magnetic field and sintered at 800°C, 1300°C, 1400°C and 1600°C. The inverse pole figures and EBSD-mapping highlights the influence of the magnetic field and sintering temperature on the texture development. The inverse pole figures calculated for the fiber direction show a major (001) component for all the samples. With the increasing sintering temperature, the texture strength is enhanced and the c-axis distribution is sharper. The effectiveness of the combined approach for determining the crystallite size is also evident. As a global trend, the calculated crystallite size and observed grain size are similar and increase with the increasing sintering temperature. The mechanism of the texture development in the sintered specimens is certainly initiated from the preferred orientation of the green body after slip-casting under a high magnetic field. The basal texture is enhanced during sintering by selective anisotropic grain growth. We evidenced here the powerfulness of the Rietveld texture analysis correlated to SEM-EBSD calculation to provide a basis for the correlation of texture, microstructural parameters and anisotropic properties.

Abstract: Ferroelectric/ferroelastic structures exhibit systematic crystallographic distortions below certain phase transition temperatures. Domains, or regions of spatial continuity in such distortions, form in a self-compensating pattern when cooled in the absence of an applied field, forming equal volume fractions of all possible states by uniform selection of crystallographic variants. An applied field (poling) can alter the volume fraction of domains within the ferroelectric phase by switching of the non-preferred orientations, a form of ferroelectric domain texture. When ceramics possess a crystallographic texture prior to inducing domain texture, the two component textures combine multiplicatively to form the complete product texture. Using tape cast bismuth titanate (Na0.5Bi4.5Ti4O15) with an initial crystallographic texture, this paper establishes the quantitative approach for resolving both the component grain and domain textures and describing the complete product texture.

Abstract: Thermoelectric oxides consisting of Bi, Pb, Sr, Y and Co are produced by usual sintering method. Uniaxial compression deformation is performed on the oxides under various deformation conditions. Melting temperature is determined by thermal analysis and deformation is conducted close to the melting point. After deformation, density, microstructure, texture and thermoelectric characteristics are experimentally examined. It is found that the oxides plastically deforms at high temperatures, resulting in an increase in density as well as the development of textures. The sharpness of the texture varies depending on deformation temperature, strain rate and the amount of strain. Microstructure observation by SEM elucidates that plastic deformation proceeds without generating severe cracks and all the grains are heavily deformed. Simple examination on the crystal structure suggests that perfect dislocation having small Burgers vector can move on {001} which coincides with the texture results.

Abstract: The influence of current density and temperature on the macrotexture, the orientation and size of grains, and the corrosion resistance of tin deposits was studied. Tin coatings with two different textures, (100) and (301) fiber textures were produced by electrodeposition at 20°C by varying current density. At a lower current density of 100A/m2, (301) fibre was obtained. At the current densities of 100 and up to 400 A/m2, only (100) fibre texture was observed. An increase in current density leads to a decrease in grain size. At the same current density, the grain size of tin coatings increases with increased temperature. The influence of temperature (20, 40, 60 and 80 °C) on texture is relatively negligible. The corrosion resistance of tin coatings increases with a decrease in grain size. The corrosion resistance of tin coating with (301) fibre is higher than that of tin coating with (100) fibre texture. The results suggest that texture and microstructure play an important role in controlling corrosion rate of tin based coatings.

Abstract: Solder joints based on Sn-Ag used in electronic systems fail due to thermomechanical fatigue (TMF) damage that develops during service. Grain boundary sliding and/or shear band formation are observed during TMF. Orientation Imaging Microscopy (OIM) was used to study the damage that develops and relate it to slip systems and the grain boundary character that is prevalent in tin. A number of special boundaries form preferentially during solidification, and those with misorientations about a [110] axis, including low angle boundaries, are more likely to slide with thermal cycling. Special boundaries aligned to have large resolved shear stress exhibit large scale sliding, and others with normal stress components exhibit fracture. Damage accumulation depends on the deformation mode, temperature, and initial crystal orientations present in the joint.

Abstract: Epitaxial thin films of the superconducting borocarbide compound YNi2B2C were grown on single crystal MgO (100) substrates without and with Y2O3 buffer layer using pulsed laser deposition (PLD). In both cases YNi2B2C grows with [001] normal to the substrate. However, the in-plane texture depends on the starting condition. For samples without buffer layer, oxygen from the substrate diffuses into the film and forms an Y2O3 reaction layer at the interface. As a consequence, a deficiency of Y is generated giving rise to the formation of secondary phases. On the other hand, using an artificial Y2O3 buffer layer secondary phases are suppressed. The texture of the Y2O3 layers determines the texture of the YNi2B2C film. The superconducting properties of the borocarbide films are discussed with respect to texture and phase purity.

Abstract: Nickel monosilicide (NiSi) is a key material in microelectronics and its thermomechanical properties play an important role in determining the stress/strain field generated in a transistor structure. The Coefficient of Thermal Expansion (CTE) is of particular importance in the determination of such a field. As NiSi is used in microelectronics in its polycrystalline form, it becomes of particular interest to study the thermomechanical behaviour of the NiSi aggregate, considered as a unique macroscopic body. The grain orientation of a 120 nm polycrystalline NiSi film grown on single crystal silicon has been studied by means of electron diffraction, and the evaluation of the CTE tensor of the film in the wafer reference frame has been performed by weighted averaging the single grain contributions. The results clearly show the importance of orientation distribution in determining the value of the equivalent coefficient of thermal expansion of the aggregate.

Abstract: Pure Ni, Ni-5at.%Mo and Ni-5at.%W prepared through P/M route have been severely cold deformed (~95%) and given different heat treatments to develop sharp cube component ({001}<100>) for coated superconductor applications. It was found that amongst the three materials studied, Ni-5at%W develops the most sharp cube texture. This is in contrary to the observation in similar materials produced by the melting and casting route.