Papers by Keyword: Crystal Orientation

Abstract: To analyze the effect of the crystal orientations and the grain size on the Young's modulus of thin polysilicon microelements, two-dimensional finite element models in plain strain condition were developed using a Voronoi structure. The number of grains in a model of a 10 μm square area was changed from 23 to 1200. The grain size and the crystal orientation of the film were analyzed by means of an electron back-scattering diffraction pattern (EBSP) method. The average grain size of the front surface of the thin film was about 0.69 μm, which is almost equal to the grain size of the Voronoi model having 300 grains. From the results of EBSP analysis, the specimen had no oriented structure. Therefore, random crystal orientation was given to each grain of the FEM models. When the number of grains increased, the Young's modulus converged on about 171 GPa and its scatter caused by the different sets of the random orientation was reduced. The Young's modulus obtained by the FEM analysis was larger than the value obtained by the tensile tests.

Abstract: The crystal orientation, surface morphology, surface roughness and scratch properties of Au/NiCr/Ta multi-layered metallic films was examined by X-ray diffraction (XRD), atomic force microscopy (AFM) and a scratch test method, respectively. It was clarified that the surface morphology and surface roughness depend on the substrate temperature. The surface roughness decreases from 4.259nm to 2.935nm when substrate temperature changed from 100°C to 180°C, and then increases when substrate temperature above 180°C. The XRD revealed that there are only Au diffraction peaks with highly textured having a Au-(111) or a mixture of Au-(111) and Au-(200) orientation. The micro-scratch test reveals that both modes can be used for conventionally critical load determination, but the friction mode can additionally reflect the changes at different metallic film layers, the critical characteristic load was not sensitive to substrate temperature.

Abstract: Through more than three decades of development, a semi-solid metal processing has been successfully established as a unique casting technique to produce a structural component for an automobile industry with high integrity and improved mechanical properties. A slurry-on-demand process to make the semi-solid slurry having a fine and globular microstructure has been very important in the semi-solid metal process. In the present study, the orientation distribution functions (ODFs) calculated from the pole figure data were examined and tried to characterize the bulky morphology of primary solid phase of the semi-solid slurry of Al-Cu alloy produced with various magnetic flux density of 100 to 300Gauss in the specially designed electromagnetic (EM) stirrer. Columnar dendritic structure of primary α phase was turned into a rosette and globular structure by EM stirring during solidification. The primary α phase was refined and globularized with increasing a magnetic flux density of EM stirring. Also, due to the EM stirring the tendency to random orientation was appeared. In the case of unstirred Al-Cu alloy the <110>//ND texture was developed strongly and <100>//ND and <111>//ND texture was weakly developed. But with the increase of the EM stirring strength, <100>//ND and <111>//ND texture were more strongly advanced. Due to EM stirring the texture was almost completely randomized.

Abstract: Through the analysis of many creep rate-strain curves of γ-single phase Ni-20mass%Cr alloy single crystals with various stress axes, it has been elucidated that the ratio of transient stage to rupture life becomes larger with decreasing the stress. And the transient stage consists of Stage I and Stage II. In Stage I, the creep rate just after loading remains constant, and in Stage II, a steep decrease in creep rate continues. It is noticeable that there is a marked difference in transient stage among single crystals with different stress axes. The aim of this study is to elucidate the mechanisms leading to the different transient stages as the function of stress axes. The deformation during transient stage in the single crystals except for the single crystals with the stress axes of the [001] and [1,–11] poles in the standard stereographic triangle, proceeds using the primary slip plane. And they are divided into two groups of the single crystals with the angle between stress axis and primary slip plane, θ, less than 45° and the single crystals with θ more than 45°. The deformations of Stage I and Stage II in these single crystals proceed using the slip system of (111)<1,–01> and the slip system of (111)<1,–10>, and in Stage I, the former slip system acts mainly except for that of single crystals with stress axis of [011]. While, in the single crystal with stress axis of [011], two slip systems above described operate at the beginning of Stage I, and the stress axis moves along [011]-[1,–11] line. And this moving gives slight increase in the Schmid factor, therefore, in Stage I slight increase in creep rate was confirmed. The {111} pole figure of the single crystal with stress axis of [1,–11] whose deformation proceeds using the plural slip planes are obtained by SEM-EBSD method. It becomes clear that the smallest strains of Stage I and Stage II derived from the increase in the torsion with creep deformation.

Abstract: Since preferential orientation of c-axis of biological apatite (BAp) crystallites depends strongly on the shape of hard tissue, closely relating to the in vivo stress distribution, it is a useful parameter to judge the bone quality. In this study, preferential alignment of BAp crystallites in original and regenerated hard tissues were analyzed by the micro-beam X-ray diffractometer (μ-XRD) with a beam spot of 50 or 100 μm in diameter. Regenerating processes of bone defects introduced artificially in the rabbit ulna or skull were healed by inserting a biodegradable gelatin hydrogel incorporating basic fibroblast growth factor-2 (FGF-2). Recovery of BAp orientation alignment depends strongly on the regenerated portion and period, which is insufficient to recover the original level, while bone mineral density (BMD) is almost improved to the original level. This means that BMD recovers prior to improvement of the BAp orientation and the related mechanical function in the regenerated tissues. Thus, reloading on the regenerated portion caused by BMD restoration is suggested to accelerate to produce the appropriate BAp preferential alignment due to the remodeling process. The BAp orientation was finally concluded to be one of the most important indices to check the regenerative degree and process in the regenerated bone under the tissue engineering technique.

Abstract: Recently, a rheocasting process has been interested to produce a structural part for an automobile industry and so the slurry-on-demand process to make the semi-solid slurry having a fine and globular microstructure has been very important to produce a high quality and cost effective part in the rheocasting process. An electromagnetic (EM) stirrer employing for a slurry making process was designed and prepared to induce simultaneously both a circumferential and vertical fluid flow of a melt in order to control a rotation angle of EM stirring of a poured melt. In the present study, the semi-solid slurry of Al-15%Cu alloy was produced in the EM stirrer and its microstructure and the orientation distribution function calculated from the pole figure data was examined in accordance with a various rotation angle of EM stirring between 0˚ (circumferential flow) and 90˚ (vertical flow). The size and morphology of primary α phase was affected with a rotation angle of EM stirring and the finest and the most globular primary α phase could be obtained at a rotation angle of EM stirring of 45˚ and 60˚. Also, due to the EM stirring the tendency to random orientation was appeared. Also, the tendency of random orientation was the most at a rotation angle of 45˚ and 60˚. Therefore, it was considered that the rotation angle of EM stirring of 45˚ and 60˚ was the most effective to induce the non-dendritic growth of primary solid phase of EM stirred Al-Cu alloy.

Abstract: The crystal plasticity finite element method (CPFEM) is probably the method with the best potential to directly incorporate crystal anisotropy and its evolution into forming simulations. However, when it comes to the simulation of bulk materials, the representation of the crystal orientation distribution function (ODF), i.e. of the statistical texture, within the CPFEM framework becomes a key issue for the efficiency of the approach. In this work two different approaches for sampling the ODF are compared. The first is the so called Texture-Component-CPFEM, where the discretisation is based on the representation of the ODF by texture components. The second approach is based on the representation of the ODF by series expansion and uses a direct mapping of the ODF represented in the form of C-coefficients to individual orientations as needed by the CPFEM. Both methods are compared using the textures of Aluminum hot band as well as cold rolled material.

Abstract: Highly oriented hydroxyapatite (HA) coatings were prepared on titanium (Ti) substrates through a radio-frequency thermal plasma spraying method. XRD patterns showed that the HA coating layer had an structure with (00l) preferred crystal orientation. TEM observation showed that 200-800 nm-width prismatic crystals were formed in HA splats and the longitudinal axis of such prismatic crystals oriented vertical to the coating's surface. TEM images also indicate that the interface between prismatic crystals became compacted. SAD pattern show that the longitudinal axis of prismatic crystals corresponds to the <001> axis of HA.

Abstract: Mesoporous HAp aggregates were composed of needle-like crystals that were aligned to the c-axes direction perpendicular to the flat surface of plate-like aggregates. The pore size distributions of the HAp aggregates increased with increasing heat treatment temperature e.g. 3-20 and 26-52 nm, respectively, before and after heat-treated at 600 °C. The adsorption proteins on the mesoporous HAp aggregates were investigated by liquid chromatography using the HAp aggregates as an adsorbent. Elution molarity ratios of acidic proteins on the mesoporous HAp aggregates before and after heat-treatment at 600 °C increased with increasing molecular weight in the order of ferritin > fibrinogen > catalase > albumin, whereas the elution molarity ratios of basic proteins were considerably lower than those of acidic proteins. These results suggested that penetration of the large size acidic proteins into the pore of the as-prepared mesoporous HAp aggregate was slightly inhibited but were the proteins could easily penetrate into the pore of the heat-treated mesoporous HAp aggregates and then were selectively adsorbed on the mesoporous wall consisting of the a-surface of the HAp aggregate. Conversely, the basic proteins could be adsorbed on the wide outer surface of the plate-like HAp aggregates. Therefore, the elution molarity ratios of basic proteins decreased with decreasing the specific surface area by the heat treatment, independent of the mesoporous structure.

Abstract: A new technology relating to crystal orientation and structure alignment has emerged by the development of superconducting technologies. Now, a high magnetic field covering a rather large space is available even in small-scale laboratories. Under this circumstance it has been found that the crystal orientation in materials can be controlled by imposition of the high magnetic field. This principle due to a magnetization force can be applied not only to magnetic materials but also to non-magnetic materials with asymmetric unit cells. In this paper, three novel processes for the crystal orientation of ceramics and metals are described.