Papers by Keyword: Pole Figure

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: Zirconium (Zr) alloys are best known for their use in nuclear reactor applications. A hexagonally close-packed structure with a low c/a ratio and very limited slip systems leads to strong textures in these alloys during fabrication processes. These alloys are used in cladding applications for encapsulating fuel pellets, and undergo various stress conditions in-service. Hence, it is necessary to understand the creep properties of Zr alloys to predict the life of reactor claddings. Due to the unique texture, the creep deformation of these alloys is anisotropic in nature. The texture of Zircaloys was determined by X-ray diffraction experiments, and expressed in terms of pole figures and crystalline orientation distribution functions. Biaxial creep testing of thin walled tubing was used to study the creep anisotropy. Creep loci evaluation based on the experimental data and model predictions are compared. It is found that the models can predict the creep loci for recrystallized alloy very well. However, they fail to explain the behavior of the cold worked alloys. When stress enhancements due to the grain boundary sliding are taken into account, the predicted creep loci correlated well with that constructed from the experimental data.

Abstract: We fabricated YBCO film using a TFA-MOD method and evaluated the phase formation, texture evolution, and critical properties as a function of the firing temperatures. In order to enhance the reaction kinetics and to control the formation of the second phases, Y2Ba1Cu1Ox and Ba3Cu5O8 powders were used as precursors (the so called “211 process”), instead of Y-, Ba-, and Cu-based acetate, and dissolved in trifluoroacetic acid (TFA). The films were calcined at 460°C and then fired at 750°C-800°C in a 12.1% humidified Ar-O2 atmosphere. We found that the microstructure varied significantly with the firing temperature; the grain grew further and the film became denser as the firing temperature increased. The textures of all of the films were similar and mainly biaxial. On the other hand, the intensity of the major and minor texture components differed from each other. For the film fired at 775°C, the critical current was obtained to be 39 A/cm-width (corresponding critical current density is 2.0 MA/cm2), which was probably attributed to such factors as the enhanced phase purity and out-of-plane texture, the moderate film density and grain size, and crack-free surface.

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: Factors controlling the recrystallization of a continuous cast Al-Fe-Ni alloy were investigated by analyzing microstructure, grain structure, texture, and electron backscattering patterns. The texture of an as-rolled sample heated at 400°C was similar to that of a sample at the reduction ratio of 50% after intermediate annealing at 550°C. The as-rolled samples had a strong (213)[36-4] (S-type) orientation that was changed to a strong (130)[3-12] (QQ-type) orientation by heating at 400°C. This recrystallization looks like continuous recrystallization. Discontinuous recrystallization due to particle-stimulated nucleation is suppressed by the fine dispersion of Al-Fe-Ni-Si particles that form during casing and intermediate annealing, and stabilize the grain and subgrain structure. We think that a course initial grain structure and moderate level of strain level are the important factors promoting continuous recrystallization in this alloy.

Abstract: In this study, the orientation distribution function (ODF), which can be calculated from the pole figure data, was examined and tried in order to characterize the bulky morphology of primary solid phase of semi-solid slurry instead of erroneous 2D observation for the characterization of microstructure. Al-15wt%Cu alloys were electromagnetically stirred during the continuous cooling in the specially designed electromagnetic (EM) stirrer, which generates a rotating magnetic field, and the samples were prepared by interrupt-quenching semi-solid slurry at a solid-liquid region. Owing to EM stirring the temperature distribution of melt inside a crucible became uniformed compared with the case of unstirred melt and the normal dendritic structure was transformed to one consisting of the spherical and rosette shaped primary solid phase due to the fragmentation of the dendrites. Also by the effect of EM stirring the <110>//ND texture were still strongly developed, but the advancement of the orientations to lead <110>//ND texture became weaker, and the orientations to lead <100>//ND and <111>//ND texture were more strongly advanced in comparison with the unstirred case. Therefore the advancement of the texture became weak and so the tendency to random orientation was appeared due to the EM stirring. Therefore it was thought that the extent of random orientation could be valued for the characterization of bulky morphology of primary solid phase of semi-solid slurry.

Abstract: We fabricated bi-axially textured pure Ni and Ni–5at.%W (Ni-5W) alloy tapes for the application of rechargeable battery cathode and coated superconductor, where the controlled microstructure of the substrate plays a critical role. The sintered Ni or Ni-W rods were cold-rolled into the thin tapes of 80 ~ 100 µm thickness, and the tapes were heat-treated for texture development with a line focused infrared heater. The temperature was maintained at 800 ~ 1050 °C, using a 1kW double ended linear halogen lamp in 96%Ar-4%H2 atmosphere. The (2 0 0) texture of Ni tape was successfully formed through optimization of the recrystallization infrared heating condition for the cold rolled Ni tapes. The full width half maximum of the Ni tapes was less than 10o, and the grain size was 20 ~ 40 µm. Focused IR-heating resulted in a better texture development and smaller grain size compared to the conventional resistive heating because of the steep temperature gradient.

Abstract: Materials exhibit microstructures and textures that influence their use and properties. Xray and neutron diffraction allow characterization of the bulk texture, whereas Electron Backscattered Diffraction (EBSD) permits determination of the local texture. In many cases Transmission Electron Microscopy (TEM) remains necessary to characterize the substructure and the local texture for highly deformed materials. Depending on the scale considered, all these complementary techniques permit the coupling of texture and microstructure so that it becomes possible to control microstructure and its evolution during a processing route. Some examples in titanium aluminides, (α + β) titanium alloys and an Fe-Ni alloy will illustrate this challenge.

Abstract: The method is described which enables to determine the microtexture that is the orientation distribution within individual grains of a polycrystal. The microtexture is evaluated on the base of X-ray pole distributions measured for separate reflections, referred to as microscopic pole figures (MPF). The procedure for treatment of experimental MPF and the following computation of orientation distribution function is described in detail. Precision of the microtexture evaluation and possible ways of its improvement are discussed. As an example of the method application, orientation distribution within a single grain of aluminum polycrystal deformed by uniaxial compression up to 50% has been examined.