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15 records found
1.
Ubhi, H. S. and A. W. Bowen (1996). "Analysis and Representation of Electron Backscattered Diffraction Texture Data - Examples from Heat-Treated Al-Li Alloy Sheet." Materials Science and Technology 12(10): 880-886.
2.
Uchic, M. D., M. Groeber, et al. (2004). "Augmenting the 3D Characterization Capability of the Dual Beam FIB-SEM." Microscopy and Microanalysis 10(Suppl. 2): 1136-1137.
3.
Ueda, M., H. Y. Yasuda, et al. (2001). "Effect of Grain Boundary Character on the Martensitic Transformation in Fe-32at.%Ni Bicrystals." Acta Materialia 49: 3421-3432.
The effect of grain boundary character on the martensitic transformation was examined in two types of Fe-32at.%Ni bicrystals containing a 90° {211} twist boundary focusing on the martensite-start temperature (Ms) during cooling, the morphology of the martensite and the variant selection. The Ms of bicrystals with a tilt boundary was higher than that of single crystals, while bicrystals with a twist boundary showed no significant difference from that of single crystals. Coarse lenticular martensites formed symmetrically in neighboring grains around the tilt boundary. In contrast, tiny martensites were uniformly distributed in bicrystals with a twist boundary, and in single crystals. In the vicinity of the tilt and twist boundaries, some variants with the habit plane almost parallel to the boundaries were preferentially selected among 24 variants. Moreover, since the equivalent variants in neighboring grains at the tilt boundary are selected, strain compatibility of the shape strain of martensite across the tilt boundary is satisfied, resulting in an increased Ms. The effect of pre-strain on the heterogeneous nucleation of martensite at the boundaries was also investigated.
4.
Ueda, M., H. Y. Yasuda, et al. (2003). "Controlling factor for nucleation of martensite at grain boundary in Fe-Ni bicrystals." Acta Materialia 51: 1007-1017.
A favourable nucleation of martensites at a grain boundary was investigated using Fe-Ni bicrystals containing a <211> symmetrical tilt boundary with various tilt angles, focusing on the martensite-start temperature (Ms), the morphology of martensites and the variant selection. Near the grain boundaries, some variants with the habit plane almost parallel to the bondaries were preferentially selected and their variants changed depending on the tilt angle. In addition, the equivalent variants were symmetrically adjoined at the boundary to maintain the compatibility of shape strains of martensites across the boundary.Such characteristic nucleation can be regarded as a self-accommmodation across the boundary, which is called cooperative nucleation (CN). The CN effectively reduces the strain energy due to the formation of martensites compared with the independent nucleation within a grain resulting in an increase in Ms. The charateristic variant selection of martensites can also be explained from the minimisation of strain energy.
5.
Ueda, M., H. Y. Yasuda, et al. (2003). Martensitic and Reverse Transformation in Fe-Ni Bicrystals. Thermec' 2003, Leganés, Madrid, Spain, Trans Tech Publications Ltd.
The effect of grain boundary on martensitic and reverse transformation ws examined using Fe-Ni bicrystals with a tilt or twist boundary. Tilt bicrystals show significantly higher martensite start temperature (Ms) than single crystals or twist bicrystals. Coarse lenticular martensites were symmetrically adjoined at the tilt boundary although tiny martensites were homogeneously distributed in twist bicrystals and single crystals. In the vicinity of boundary, some variants with the habit plane almost parallel to the boundary were preferentially selected among 24 habit plane variants irrespective of boundary type. Furthermore, equivalent variants were adjoined at the tilt boundary. Such characteristic nucleation of martensites can be regarded as an example of self-accommodation across the boundary, which is called cooperative nucleation (C-N). The C-N must enhance the heterogeneous nucleation of martensites at the boundary since it effectively reduces the strain energy due to the formation of martensites. On the other hand C-N led to the retardation of reverse transformation on heating and the formation of numerous sub-boundaries in reversed γ phase near the tilt boundary. Thus the transformation behavior in bicrytals was found to depend strongly on the grain boundary character.
6.
Uetsuji, Y., T. Yoshida, et al. (2005). "Evaluation of ferroelectric properties of piezoelectric ceramics based on crystallographic homogenization method and crystal orientation analysis by SEM/EBSD technique." Nippon Kikai Gakkai Ronbunshu, A Hen (Transactions of the Japan Society of Mechanical Engineers, Part A) 71(2): 241-246.
Macroscopic ferroelectric properties of piezoelectric polycrystals are strongly affected by microscopic non-homogeneous crystal structure. In our previous study, a multi-scale finite element procedure based on crystallographic homogenization method has been developed to predict macroscopic properties by considering microscopic crystal morphology. In this study, a crystal orientation distribution of polycrystalline barium titanate has been measured by SEM/EBSD technique, and it has been introduced to the microscopic finite element model, which satisfies the periodicity. As the prediction of macroscopic properties depends on the sampling conditions of the measured crystal orientations, the effects of number of sampling points and sampling area have been investigated. Additionally, the influence of dispersion of crystal morphology on macroscopic ferroelectric properties has been discussed.
7.
Ullemeyer, K., G. Braun, et al. (2000). "Texture analysis of a muscovite-bearing quartzite: a comparison of some currently used techniques." Journal of Structural Geology 22(11-12): 1541-1557.
Four well-established techniques were applied to determine the mineral textures of a muscovite-bearing quartzite: (1) directional measurements on an optical U-stage; (2) X-ray; (3) neutron; and (4) electron diffraction (EBSD). Techniques (1) and (4) are of the ‘single grain’ type and techniques (2) and (3) of the ‘statistical’ or ‘volume’ type. Experimental pole density diagrams were compared by means of the construction of pole figure differences (‘difference pole figures’), which led to the observation that EBSD- and U-stage derived pole figures agree well, even in detail. In contrast, pole figures derived from X-ray and neutron diffraction are clearly different from pole figures derived from the single grain techniques, visible as pronounced preferred orientation in the difference pole figures. Specific properties of the applied techniques may be responsible for the observed differences, such as (1) missing proportionality to the grain volume in the single grain methods, (2) the accessible sample volume, (3) erroneous data correction, or (4) statistical errors. Also the method of data treatment, which is basically different for the single grain and statistical methods, should be considered when pole figures are evaluated. Apart from purely economical constraints and availibility of equipment, the decision on the most suitable method for a texture determination should be based on the scientific goals and specific properties of particular techniques. Texture measurements of the statistical type are well suited for determination of bulk textures of rocks (e.g. as required for the calculation of anisotropic physical properties of rocks), whereas single grain measurements are advantageous for the investigation of local textures and texture forming mechanisms.
8.
Ullrich, H. J. (1990). "Progress in the Field of Kossel and Pseudo-Kossel Technique." Mikrochimica Acta 2(1-6): 19-24.
9.
Ullrich, H. J., A. Uhlig, et al. (1992). "Precise Determination of the Lattice-Constant of LiF by Means of X-Ray Divergent Beam (Pseudo-Kossel) Technique via Computer-Graphics and Multiple Intersections." Mikrochimica Acta 107(3-6): 283-293.
10.
Ulrich, S. and D. Mainprice (2005). "Does cation ordering in omphacite influence development of lattice-preferred orientation?" Journal of Structural Geology 27(3): 419-431.
Three mantle eclogite xenoliths from the Robert Victor mine in South Africa were studied. The calculated pT conditions are p≥4.5 GPa and T between 950 and 1145 °C. The clinopyroxene has a jadeite component between 0.19 and 0.52. In-situ, at these compositions and temperatures clinopyroxene (omphacite) has the high temperature C2/c structure, which has perfect cation disordering. The lattice preferred orientation (LPO) of clinopyroxene in the samples of different microstructure and composition has been measured by EBSD The LPO for all three samples is characterized by a strong alignment of the [001] axes with the lineation, typical of the 'L-type' or 'LS-type' patterns for omphacite. These data disagree with a cation-ordering model for dislocation slip, which predicts a 'S-type' LPO pattern with the [001] axes forming a girdle in the foliation plane. Numerical simulation using the VPSC model has been undertaken to show the influence of the <110> {110} slip system on the LPO development in axially symmetric compression and extension, and pure and simple shear. The activity of the <110 >{110} system should be very sensitive to changes in the cation ordering as the clinopyroxene goes towards the low temperature fully ordered P2/n structure. Increasing the critical resolved shear stress on this system from 1 to 10, resulted in a decrease of the slip activity of 80%, but produced no significant changes to the LPO. The most important slip systems for LPO development are [001] (100), [100] (010) and [001] (010) in all simulations. The LS-index is introduced to quantify the symmetry of omphacite LPO. The index is based on the eigenvalues of the (010) and [001] pole figures, and has a value of one for the end-member L-type, zero for the end-member S-type and intermediate values for LS-types. The naturally deformed omphacite LPOs have LS-indexes of between 0.61 and 0.85 confirming they are LS-types, but closer to the L-type end-member. In the VPSC models the S-type end-member develops in axially symmetric compression (LS-index≈0), whereas the L-type end-member develops in axially symmetric extension (LS-index≈1). In simple and pure shear the LS-type fabric develops with LS-index of between 0.55 and 0.60. The VPSC simulations show that the LS-index is nearly constant with increasing strain for a constant macroscopic velocity gradient, which prescribes the constant strain path. We conclude that development of S- and L-type LPOs in omphacite is controlled by the strain path and that the LS-index is a useful quantitative indicator of fabric symmetry.
11.
Une, K., K. Nogita, et al. (2004). "Crystallography of zirconium hydrides in recrystallized Zircaloy-2 fuel cladding by electron backscatter diffraction." Journal of Nuclear Science and Technology 41(7): 731-740.
Precipitation morphology and habit planes of the delta -phase Zr hydrides, which were precipitated within the alpha -phase matrix grains and along the grain boundaries of recrystallized Zircaloy-2 cladding tube, have been examined by electron backscatter diffraction (EBSD). Radially-oriented hydrides, induced by residual tensile stress, precipitated in the outside region of the cladding, and circumferentially-oriented hydrides in the stress-free middle region of the cladding. The most common crystallographic relationship for both types of the hydrides precipitated at the inter- and intra-granular sites was identical at (0001)α{111}δ, with {1017}α//{111}δbeing the occasional exception only for the intergranular radial hydrides. When tensile stress was loaded, the intragranular hydrides tended to preferentially precipitate in the grains with circumferential basal pole textures. The intergranular hydrides tended to preferentially precipitate on the grain faces opposite to tensile axis. The change of prioritization in the precipitation sites for the hydrides due to tensile stress could be explained in terms of the relaxation effect of constrained elastic energy on the terminal solid solubility of hydrogen at hydride precipitation.
12.
Ushigami, Y., S. Nakamura, et al. (2002). Effect of Grain Boundary Character on Selective Growth of Goss Grain in Fe-3%Si Alloy. ICOTOM 13, Seoul, Korea, Trans Tech Publications Inc.
Effect of grain boundary character on the selective growth of Goss grain during secondary recrystallization has been investigated. Grain growth behavior of secondary recrystallized Goss grain was observed in situ by synchotron x-ray topography, and orientation relationship between the Goss grain and the preferentially consumed grains in the primary matrix was analyzed by EBSP technique. Grain growth of Goss grain is classified into two regions: (1)inhomogeneous and sluggish grain growth in the lower transition temperature region and (2) uniform and stationary grain growth in the higher temperature region. Goss grain grows preferentially into the matrix grains with near-sigma 9 boundaries (within the twice of misorientation angle due to the Brandon's criterion) in the lower transition temperature region, where most of the general boundaries are stagnated, which leads to inhomogeneous and sluggish grain growth. As annealing temperature rises, the inhibitor intensity decreases and pinning of general boundaries gradually fade out, which leads to uniform and stationary grain growth. Goss grain is frequently bounded by near-sigma 9 boundaries and thus grows selectively in the lower transition temperature region.
13.
Ushigami, Y., T. Kumano, et al. (2004). Secondary Recrystallization in Grain-Oriented Silicon Steel. Second Joint International Conference on Recrystallization and Grain Growth, ReX & GG2, SF2M, Annecy, France, Trans Tech Publications Ltd.
Mechanism of Goss secondary recrystallization in grain-oriented silicon steel has been investigated by temprature gradient annealing and by in situ observation utilizing synchotron x-ray topography. The results support the selective growth theory. Migration of Goss grains is controllled by second phase particles (inhibitor); and sharper Goss grains, which have higher frequency of CSL boundaries to the matrix, start to grow preferentially while the other matrix grains are stagnated by inhibitor. CSL boundaries are supposed to have lower grain boundary energy, thus suffer lower pinning force from the inhibitor and start to migrate at higher inhibition level. Based on this model, we have made a computer simulation and have found that this model successfully depicts the important features of secondary recrystallization: grain growth behavior of secondary grains, secondary grain size and sharpness of Goss texture.
14.
Utsunomiya, H., M. P. F. Sutcliffe, et al. (2004). "Evolution of matt surface topography in aluminium pack rolling. Part I: model development." International Journal of Mechanical Sciences 46(9): 1349-1364.
Roughening of the matt surface of pack rolled aluminium foil has been modelled. The model is based on the finite element method using isotropic plasticity. A distribution in material properties has been used to simulate the distribution of grain orientations through the material. It is found that the formation of shear bands causes roughening of the matt surface. The length of these shear bands allows individual grains or the hard roll to influence the roughness a significant distance away. Results show the effect of the ratio of the grain size to the strip thickness on the predicted roughness generated. The predictions show good qualitative agreement with the reported experiments. It is concluded that the model is able to simulate efficiently the effect of the granular behaviour of polycrystals on the matt surface roughness.
15.
Utsunomiya, H., M. P. F. Sutcliffe, et al. (2004). "Evolution of matt surface topography in aluminium pack rolling. Part II: effect of material properties." International Journal of Mechanical Sciences 46(9): 1365-1375.
A model has been presented in a companion paper [1] to predict the generation of roughness on the matt surface in pack rolling of aluminium foil. The model is based on the finite element method using isotropic plasticity. This model is used in the current paper to investigate the effect of material properties on the generation of surface roughness. There is a large inhomogeneity of strain during deformation, with harder grains generally deforming less than softer ones. It is found that the roughness amplitude is roughly proportional to the standard deviation of the initial grain yield stress distribution, normalised by the initial mean yield stress, so that a wider distribution of the initial yield stress results in greater surface roughness. It is shown that a suitable linear hardening law can be used to approximate the roughening behaviour for real material flow stress curves.
15 records found
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