Home About us Contact
|
Home About us Contact | ||
|
|
||
Twin Boundaries (twin + boundary)
Selected AbstractsEBSD investigation of intergranular corrosion attack on low interstitial stainless steelMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 6 2004T. Kuníková Abstract Grain boundary effect on corrosion behaviour of low interstitial AISI 316LN austenitic stainless steel after homogenization and heat treatment at 700 and 800°C was investigated by means of Electron Backscattered Diffraction (EBSD) technique. Rapid oxalic acid etch test (ASTM A262- practice A) was used to determine steel susceptibility to intergranular corrosion. An attempt to quantify oxalic acid etch test results was also made. Beneficial effect of low carbon and nitrogen content on grain boundary precipitation and corrosion was observed. No changes neither in grain orientations nor in grain boundary types between sensitised and non-sensitised steel states using orientation measurements were recorded. Twin boundaries were found in all samples with highest amount and only small occurrence changes. CSL categorizations showed only little increase of special boundary fractions with increasing time and temperature of heat treatment. Irrespective to annealing conditions a continued network of random boundaries was retained. Additionally, based on misorientation measurement of 50 grooved grain boundaries, a tendency for preferred attack of high angle boundaries (30,55°) was noted. [source] Microtexture and Grain Boundaries in Freestanding CVD Diamond Films: Growth and Twinning MechanismsADVANCED FUNCTIONAL MATERIALS, Issue 24 2009Tao Liu Abstract Three groups of free-standing chemical vapor deposition (CVD) diamond films formed with variations in substrate temperature, methane concentration, and film thickness are analyzed using high-resolution electron back-scattering diffraction. Primarily {001}, {110}, and {111} fiber textures are observed. In addition, corresponding primary and higher order twinning components are found. As interfaces, high angle, low angle, primary twin, and secondary twin boundaries are observed. A growth and a twinning model are proposed based on the sp3 hybridization of the bond in the CH4 molecule that is used as the deposition medium. [source] Copper Nanowires with a Five-Twinned Structure Grown by Chemical Vapor Deposition,ADVANCED MATERIALS, Issue 10 2008Changwook Kim Freestanding copper nanowires (CuNWs) grown by CVD are analyzed by electron microscopy to show the details of a fivefold-twinned structure. The electron diffraction pattern discloses irregular mismatching of the twin boundaries. The electron emission characteristics of the CuNWs are presented, along with a CuNW-based proof-of-principle field-emission display (see figure). [source] Recrystallization behaviour of the nickel-based alloy 80 A during hot formingJOURNAL OF MICROSCOPY, Issue 3 2007S. MITSCHE Summary The dynamic recrystallization as well as meta-dynamic and static recrystallization of the nickel-based alloy 80A was investigated by means of electron backscatter diffraction (EBSD). Specimens were hot compressed at a temperature of 1120°C and a strain rate of 0.1/s at varying strain and soak times to describe the recrystallization behaviour. Various approaches were tested in order to differentiate between recrystallized and deformed grains based on EBSD data. The grain orientation spread was clearly found to be the most reliable procedure. A high twinning of the recrystallized grains was observed, and as a consequence the measured grain size was strongly dependent on whether the coherent and incoherent twin boundaries were regarded as genuine boundaries or removed. [source] EBSD and TEM investigation of the hot deformation substructure characteristics of a type 316L austenitic stainless steelJOURNAL OF MICROSCOPY, Issue 3 2004P. Cizek Summary The evolution of crystallographic texture and deformation substructure was studied in a type 316L austenitic stainless steel, deformed in rolling at 900 °C to true strain levels of about 0.3 and 0.7. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used in the investigation and a comparison of the substructural characteristics obtained by these techniques was made. At the lower strain level, the deformation substructure observed by EBSD appeared to be rather poorly developed. There was considerable evidence of a rotation of the pre-existing twin boundaries from their original orientation relationship, as well as the formation of highly distorted grain boundary regions. In TEM, at this strain level, the substructure was more clearly revealed, although it appeared rather inhomogeneously developed from grain to grain. The subgrains were frequently elongated and their boundaries often approximated to traces of {111} slip planes. The corresponding misorientations were small and largely displayed a non-cumulative character. At the larger strain, the substructure within most grains became well developed and the corresponding misorientations increased. This resulted in better detection of sub-boundaries by EBSD, although the percentage of indexing slightly decreased. TEM revealed splitting of some sub-boundaries to form fine microbands, as well as the localized formation of microshear bands. The substructural characteristics observed by EBSD, in particular at the larger strain, generally appeared to compare well with those obtained using TEM. With increased strain level, the mean subgrain size became finer, the corresponding mean misorientation angle increased and both these characteristics became less dependent on a particular grain orientation. The statistically representative data obtained will assist in the development of physically based models of microstructural evolution during thermomechanical processing of austenitic stainless steels. [source] Improvement in Hydration Reactivity of ,-Phase Belite by Remelting ReactionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2001Koichiro Fukuda The hydration reactivity of the ,-phase belite, containing small amounts of Na2O, Al2O3, and Fe2O3, was significantly improved by the remelting reaction. The remelted belite, in which the reaction sufficiently occurred, was exclusively composed of the twinned ,-phase. The liquid, which was exsolved by the reaction, concentrated the Na2O component. Both the exsolved alkali and the twin boundaries accelerated the early stage of the hydration; the 2 d cumulative heat evolution of the remelted belite (,120 J/g) was about twice that of the ,-phase belite (,65 J/g). The grindability was also improved by the remelting reaction, which agreed with previous studies. [source] Modelling of magneto-mechanical hysteresis loops in Ni-Mn-Ga shape memory alloysPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004Laurent HirsingerArticle first published online: 17 DEC 200 Abstract A predictive model of field-induced strain in Ni-Mn-Ga ferromagnetic shape memory alloys is proposed. In this study, magnetocrystalline anisotropy K1 is introduced to permit magnetisation rotation in martensite platelets. The demagnetisation field induced by the shape of platelets is investigated. The proposed model is identified on experiments performed by Straka et al. This identification shows that observed macroscopic hysteresis loops, i.e. magnetisation and detwinning strain versus applied magnetic field, correspond exactly to a successive activation of three mechanisms: Movement of 180° domain walls, rotation of magnetisation and martensite detwinning. As expected, magnetization and strain -induced by magnetic field- in a single crystal are mainly given by the mobility of twin boundaries and magnetic anisotropies (due to the martensite crystallographic structure and to the shape of platelets). (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Order,disorder twinning model and stacking faults in ,-NTOACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2006Dieter Schwarzenbach Crystals of the recently published [Bolotina, Kirschbaum & Pinkerton (2005). Acta Cryst. B61, 577,584] triclinic (P) structure of 5-nitro-2,4-dihydro-1,2,4-triazol-3-one (,-NTO) occur as fourfold twins. There are Z, = 4 independent molecules per asymmetric unit. We show that the structure contains layers with 2-periodic layer-group symmetry p21/b 1 (1). This symmetry is lost through the stacking of the layers, which is a possible explanation for Z, = 4. A layer can assume four different but equivalent positions with respect to its nearest neighbor. Twinning arises through stacking faults and is an instructive example of the application of order,disorder theory using local symmetry operations. The near-neighbor relations between molecules remain unchanged through all twin boundaries. The four structures with maximum degree of order, one of which is the observed one, and the family reflections common to all domains are identified. Rods of weak diffuse scattering confirm the stacking model. [source] Carbothermal Synthesis of ,-SiC Micro-RibbonsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2008Gleb N. Yushin We report the synthesis of microscopic ,-SiC ribbons (belts) on the surface of a graphite rod at 1800°,1900°C by a carbothermal process. The width of the ribbons produced ranged from 500 nm to 5 ,m and the aspect ratio was up to 400. The ribbon thickness ranged from 50 to 800 nm. Their growth mechanism was explained by accelerated growth along the twin boundary. SiC whiskers grew on the rod along with the ribbons. Frequently, ribbons were growing from the tip of a whisker or whiskers were growing from the edge of a ribbon. SiC ribbons may find applications in high-temperature sensors, photo-electronic devices, or robust cantilevers in micro (or nano) electro mechanical systems. Alternatively, they can be used as reinforcements in composite materials, conferring anisotropic mechanical properties, such as unidirectional flexibility, to the composite. [source] Examination of an unusual grain boundary in CaF2PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004M.E. Msall Abstract We have examined a grain boundary in CaF2 using Phonon Imaging and Electron Backscatter Diffractometry (EBSD). Unlike the <111> twin boundary typically found in CaF2, the crystal grains on either side of the boundary are not simply related to any principle symmetry directions, and are not related to one another by symmetry operations of the cubic group. In spite of the high degree of misalignment of the crystalline lattices, phonons can pass this grain boundary without excessive energy loss. Phonon images of samples taken from different sections of the grain boundary show that the structural properties of the grain boundary are constant over a large area. Computer simulations of phonon scattering at the interface based on acoustic mismatch models demonstrate that the caustic positions are sensitive to small changes in the relative orientation of the two pieces and to the projection of the grain boundary on the image plane. EBSD gives the needed high precision measurement of the relative orientation, resulting in a superior model of phonon transmission through this very asymmetric interface. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||