Texture Formation and Improvement of Grain Boundary Weak‐Links in Tape Shaped Wire Prepared by the Unidirectional Solidification Technique.

1989 ◽  
Vol 169 ◽  
Author(s):  
Michiya Okada ◽  
Toyotaka Yuasa ◽  
Tosimi Matsumoto ◽  
Katuzo Aihara ◽  
Masahiro Seido ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Fine Particles ◽  
Unidirectional Solidification ◽  
Weak Links ◽  
Second Phase ◽  
Texture Formation

AbstractAu‐Sheathed Y‐Ba‐Cu‐O(YBCO) and Tl‐Ba/Sr‐Ca‐Cu‐O(TBSCCO) tapes were fabricated by the drawing‐rolling and subsequent unidirectional solidification. A typical microstructure of melt‐textured polycrystallite including fine particles of second phase(e.q. Y‐211) was observed. The Tl‐2223 tapes prepared at an optimized condition yielded Jc=15,300 A/cm2 at 77K in the absence of magnetic field, and l,100A/cm2 in a magnetic field of IT. The enhancement of Jc in a magnetic field is suggested to be due to the improvement of weak‐links in grain boundaries.

Morphology of Σ3{/70.53°} grain boundaries in a C15 intermetallic compound

1994 ◽  
Vol 52 ◽  
pp. 684-685
Author(s):  
Fuming Chu ◽  
D. P. Pope ◽  
D. S. Zhou ◽  
T. E. Mitchell
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Crystallographic Analysis ◽  
Laves Phase ◽  
Second Phase ◽  
Bright Field Image ◽  
Boundary Edge ◽  
Arc Melting ◽  
Fcc Lattice ◽  
Diffraction Patterns

A C15 Laves phase, HfV2+Nb, shows promising mechanical properties and here we describe the structure of its grain boundaries. The C15 Laves phase has a fcc lattice with a=7.4Å. An alloy of composition Hf14V64Nb22 (including a C15 matrix and a second phase of V-rich bcc solution) was made by arc-melting. The alloy was homogenized at 1200°C for 120h. Preliminary study concentrated on Σ3{<110>/70.53°} grain boundaries in the C15 phase using Philips 400T and CM 30 microscopes.The most-commonly observed morphology of Σ3{<110>/70.53°} grain boundaries in the C15 phase is a faceted boundary. A bright field image (BFI) of the faceted boundary and the corresponding diffraction patterns with the grain boundary edge-on are shown in Fig. 1(a). From the diffraction patterns using a <110> zone axis for both grains, it is obvious that this is a Σ3{<110>/70.53°} grain boundary. Crystallographic analysis shows that the Σ3{<110>/70.53°} grain boundaries selectively facet with the following relationships between the two grains: {111}1//{111}2, {112}1//{112}2, {111}1//{115}2, and {001}1//{221}2.

Research on Micro-Mechanism of Nanocomposite Ceramic in Two-Dimensional Ultrasound Grinding

2007 ◽  
Vol 359-360 ◽  
pp. 344-348 ◽  
Author(s):  
Bo Zhao ◽  
Yan Wu ◽  
Guo Fu Gao ◽  
Feng Jiao
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Deformation Mechanism ◽  
Ground Surface ◽  
Grain Boundary Sliding ◽  
Second Phase ◽  
Two Dimensional ◽  
Composite Ceramics ◽  
Nano Composite ◽  
Boundary Sliding

Surface microstructure of nano-composite ceramics prepared by mixed coherence system and machined by two-dimensional ultrasonic precision grinding was researched using TEM, SEM, XRD detector and other equipments. Structure, formation mechanism and characteristic of metamorphic layer of ground surface of nano-composite ceramics were researched. The experiment shows micro deformation mechanism of ceramic material in two-dimensional ultrasound grinding is twin grain boundary and grain-boundary sliding for Al2O3, and it is crystal dislocation of enhanced phase, matrix grain boundary sliding, coordination deformation of intergranular second phase as well as its deformation mechanism for nano-composite ceramics. The fracture surfaces of nano-composite materials with different microscopic structure were observed using TEM and SEM. Research shows that ZrO2 plays an important influence on the generation and expansion of crack, and enhances the strength of grain boundaries. When grain boundaries is rich in the ZrO2 particles, the crack produced in grinding process will be prevented, and the surface with plastic deformation will be smooth. The results shows nanoparticles dispersed in grain boundary prevents crack propagation and makes materials fracture transgranularly which makes the processed surface fine.

Annealing in a Natural Laboratory: an EBSD and Cl Study of Calcite and Quartz Growth from Volumes of Rock Heated by a Nearby Melt Intrusion

2007 ◽  
Vol 550 ◽  
pp. 333-338 ◽  
Author(s):  
Sandra Piazolo ◽  
David J. Prior ◽  
M.D. Holness ◽  
Andreas O. Harstad
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Crystallographic Orientation ◽  
Lattice Distortion ◽  
Temperature History ◽  
Second Phase ◽  
Gradual Change ◽  
Twin Boundaries ◽  
Second Phase Particles ◽  
Crystallographic Orientations

Annealing is an important mechanism of microstructural modification both in rocks and metals. In order to relate directly changes in crystallographic orientation to migrating boundaries the researcher has the option to investigate either samples where the grain boundary motion can be directly tracked or a series of samples exhibiting successively higher degrees of annealing. Here we present results from rock samples collected from two well characterised contact aureoles (a volume of rock heated by the intrusion of a melt in its vicinity): One quartz sample in which patterns revealed by Cathodoluminescence (CL) indicate the movement of grain boundaries and a series of calcite samples of known temperature history. Electron backscatter diffraction (EBSD) analysis is used to link the movement of grain, twin boundaries and substructures with the crystallographic orientation / misorientation of a respective boundary. Results from the quartz bearing rock show: (a) propagation of substructures and twin boundaries in swept areas both parallel and at an angle to the growth direction, (b) development of slightly different crystallographic orientations and new twin boundaries at both the growth interfaces and within the swept area, and (c) a gradual change in crystallographic orientation in the direction of growth. Observations are compatible with a growth mechanism where single atoms are attached and detached both at random and at preferential sites i.e. crystallographically controlled sites or kinks in boundary ledges. Strain fields caused by defects and/or trace element incorporation may facilitate nucleation sites for new crystallographic orientations at distinct growth interfaces but also at continuously migrating boundaries. Calcite samples show with increasing duration and temperature of annealing: (a) systematic decrease of the relative frequency of low angle grain boundaries (gbs), (b) decrease in lattice distortion within grains, (c) development of distinct subgrains with little internal lattice distortion, (d) change in lobateness of gbs and frequency of facet parallel gbs and (e) change in position of second phase particles. These observations point to an increasing influence of grain boundary anisotropy with increasing annealing temperature, while at the same time the influence of second phase particles and subtle driving-force variations decrease. This study illustrates the usefulness of using samples from natural laboratories and combining different analysis techniques in microprocess analysis.

Wetting Transitions of Grain Boundaries

1999 ◽  
Vol 586 ◽  
Author(s):  
John Blendell
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Abrupt Change ◽  
Equilibrium Shape ◽  
Second Phase ◽  
Curved Surfaces ◽  
Wetting Layer ◽  
Wetting Transitions ◽  
Microscopic Morphology ◽  
Morphology Changes

ABSTRACTIt has been shown that the concepts used to determine the equilibrium shape of crystals can be extended to determine the conditions under which grain boundaries will be fully wetted, partially wetted, or not wetted by a second phase. Recent experimental observations on the equilibrated morphologies of solid or fluid wetting phases along grain boundaries, reveal features that are predicted, and in some cases required, by this construction. Theory distinguishes between cases where surfaces are smoothly curved or where there are facets, edges and corners. In the latter case the conventional comparison of the energy of the original grain boundary with the sum of the surface energy of the two surfaces of the wetting layer leads to erroneous predictions. The correct predictions are obtained by comparing the Wulff shape of the grain boundary (the interfacial energy minimizing shape for a fixed volume of material) with a carefully defined sum of Wulff shapes of the surfaces of the wetting layer. Where orientations that are wetted join with those that are not, there is almost always an abrupt change of orientation. Faceting on two hierarchical levels can occur. Microscopic morphology changes along macroscopically curved surfaces follow well defined rules predicted by theory. The analogy between the thermodynamics of interface faceting and phase transformations allows the well known concepts of phase equilibria to be used to understand the predicted structures. The predictions of the model will be used to identify the nature of the faceting observed in alumina in the presence of a second phase.

Measurement of compositional changes accompanying solid-state transformations at grain boundaries in metals

1987 ◽  
Vol 45 ◽  
pp. 296-299
Author(s):  
Ernest L. Hall ◽  
Clyde L. Briant
Keyword(s):  
Solid State ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Precipitation Process ◽  
Second Phase ◽  
Slow Cooling ◽  
Collector Plate ◽  
Compositional Changes ◽  
Property Changes ◽  
Boundary Chemistry

In many multicomponent metallic systems, solid-state precipitation processes can occur upon slow cooling or isothermal aging of solutionized material. Frequently, the precipitates form at grain boundaries, which are preferred sites for the nucleation and growth of the second phase. The precipitates generally grow through a combination of matrix and grain boundary diffusion, in which the grain boundary acts as a collector plate for the delivery of the solute to the growing precipitate. The precipitation process is thus accompanied by significant changes in the chemistry of the grain boundary and matrix regions near the grain boundary. These grain boundary chemistry changes can have a profound effect on the macroscopic properties of the material, including corrosion resistance, strength, and ductility. In order to understand the mechanism associated with these property changes, it is necessary to obtain a complete and precise description of the magnitude and extent of the compositional changes which have occurred at the grain boundaries.

Pseudopartial Grain Boundary Wetting: Key to the Thin Intergranular Layers

2013 ◽  
Vol 333 ◽  
pp. 175-192 ◽  
Author(s):  
Boris B. Straumal ◽  
Alexey Rodin ◽  
A.E. Shotanov ◽  
Alexander B. Straumal ◽  
Olga A. Kogtenkova ◽  
...  
Keyword(s):  
Contact Angle ◽  
Phase Transitions ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Thin Layers ◽  
Second Phase ◽  
Triple Junctions ◽  
Complete Wetting ◽  
Grain Boundary Wetting

The thin layers of a second phase (also called complexions) in grain boundaries (GB) and triple junctions (TJs) are more and more frequently observed in polycrystals. The prewetting (or premelting) phase transitions were the first phenomena proposed to explain their existence. The deficit of the wetting phase in case of complete wetting can also lead to the formation of thin GB and TJ phases. However, only the phenomenon of pseudopartial (or pseudoincomplete, or constrained complete) wetting permitted to explain, how the thin GB film can exist in the equilibrium with GB lenses of a second phase with non-zero contact angle.

Grain Boundary Structure as a Function of Aluminum Level in Ni3Al

1990 ◽  
Vol 213 ◽  
Author(s):  
J.A. Horton ◽  
C.T. Liu ◽  
S.J. Pennycook
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Structure ◽  
Boundary Phase ◽  
Second Phase ◽  
Contrast Imaging ◽  
Minimum Width ◽  
Undoped Material ◽  
Boron Doped ◽  
Aluminum Level

ABSTRACTUnderstanding the boron effect in Ni3Al currently centers on determining thestructure of the region near grain boundaries, especially the presence of a disordered γ phase. In this study, a series of alloys was examined by transmission electron microscopy (TEM) as a function of aluminum level, boron level, and cooling rate for thepresence of any grain boundary phases. The base alloy series all contained 0.5 at. % Hf. At 21.5 at. % Al,γ formed in the matrix as expected. However, in slowly cooled specimens with 22 and 22.5% Al, a second phase with thicknesses from 25 to 50 nm formed on some of the grain boundaries. At higher aluminum levels no evidence of any second phase was observed. The minimum width of grain boundary images formed by normal diffraction contrast imaging was generally 0.5 to 1 nm for grain boundaries that presumably had no second phase and were parallel to the electron beam. Therefore, a second phase with a thickness of 1 nm or less would not be discernable by TEM. High resolution Z-contrast imaging by scanning TEM of a very low angle boundary in directionally solidified (DS) material also showed no evidence of disordering, but did show a surprising amount of non-planarity of the boundary.Whereas slower cooling rates might be expected to aid the formation of any grain boundary phase and thereby increase the ductility, the ductility was slightly lower for the more slowly cooled alloys than for the furnace cooled alloys. From 21.5 to 24% Al, the tensile elongations remain fairly constant with values ranging from 45 to 52%. Above 24%, the ductility drops off rapidly but is still much higher for the boron-doped material than for the undoped material. At 25.2% Al, the ductility is still 4% as compared to essentially zero for undoped material. Therefore the ductility improvements in boron-doped Ni3Al do not require the presence of any grain boundary disordered phases discernable by TEM.

YBa2Cu3O7−x Grain Boundary Weak Links on MgO Bicrystal

1992 ◽  
Vol 275 ◽  
Author(s):  
H. B. Lu ◽  
S. L. Tu ◽  
J. J. Wang ◽  
J. Lin ◽  
T. W. Huang ◽  
...  
Keyword(s):  
Thin Films ◽  
Laser Ablation ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Weak Link ◽  
Weak Links ◽  
Artificial Boundaries ◽  
Tilt Boundaries ◽  
Preliminary Study ◽  
High Degree

ABSTRACTThe characteristics of YBa2Cu3O7−x (YBCO) thin films by laser ablation on MgO bicrystals have been investigated. The bicrystals were fabricated by hot pressing two single crystals with the configuration of [001] tilt boundaries. The YBCO films were epitaxial grown with C-axis normal to the both adjacent grains of bicrystals. The FWHM about (005) reflection was 0.4–0.5 degree, indicating the high degree of the oriention for the film with small mosaic spread. Our preliminary study showed that the typical value of Jc on either side of the bicrystal boundary was 0.4–10×106 A/cm2 at 15K, while that across the 10° tilt boundaries was 0.3–9×105 A/cm2 at 15K. These results implied that the artificial grain boundaries effectively weakened the supercurrent, and therefore, the weak-link properties of artificial boundaries were more easily controllable than those of naturally occuring grain boundaries.

scholarly journals Location and distribution of micro-inclusions in the EDML and NEEM ice cores using optical microscopy and in-situ Raman spectroscopy

2016 ◽  
Author(s):  
Jan Eichler ◽  
Ina Kleitz ◽  
Maddalena Bayer ◽  
Daniela Jansen ◽  
Sepp Kipfstuhl ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Large Scale ◽  
Flow Behavior ◽  
Ice Cores ◽  
Second Phase ◽  
Impurity Effect ◽  
Polar Ice

Abstract. Impurities control a variety of physical properties of polar ice. Their impact can be observed at all scales – from the microstructure (e.g., grain size and orientation) to the ice sheet flow behavior (e.g., borehole tilting and closure). Most impurities are likely to form micrometer-sized second phase inclusions. It has been suggested that these particles control the grain size of polycrystalline ice by the pinning of grain boundaries (Zener pinning), which should be reflected in the distribution of the inclusions in relation to the grain boundary network. We used an optical microscope to generate high-resolution large-scale maps (3 μm pix−1, 8 × 2 cm2) of the distribution of micro-inclusions in four samples from the EDML (Antarctica) and NEEM (Greenland) polar ice cores. The in-situ positions of more than 5000 μ-inclusions have been determined. A Raman microscope was used to confirm the extrinsic nature of a sample proportion of the mapped inclusions. A superposition of the 2D grain boundary network and μ-inclusion distributions show no significant correlations between grain boundaries and μ-inclusions. In particular, no signs could be found of grain boundaries harvesting μ-inclusions, no evidence of μ-inclusions inhibiting grain boundary migration by slow mode pinning could be detected. Consequences for our understanding of the impurity effect on ice microstructure and rheology are discussed.

TRANSPORT PROPERTIES OF JOSEPHSON JUNCTIONS AND SQUIDS EMPLOYING DIFFERENT TYPES OF YBCO GRAIN BOUNDARIES OBTAINED THROUGH THE BIEPITAXIAL TECHNIQUE

2000 ◽  
Vol 14 (25n27) ◽  
pp. 3074-3079 ◽  
Author(s):  
F. CARILLO ◽  
F. LOMBARDI ◽  
F. MILETTO GRANOZIO ◽  
V. PUNZO ◽  
F. RICCI ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Experimental Evidence ◽  
Transport Properties ◽  
Circuit Design ◽  
Quantum Interference ◽  
Superconducting Quantum Interference Devices ◽  
Different Types ◽  
Seed Layers

Concepts and experimental procedures to obtain different types of YBa 2 Cu 3 O 7 grain boundaries Josephson junction through the biepitaxial technique have been developed. Various seed layers (MgO, CeO 2 and SrTiO 3) and substrates (MgO, SrTiO 3) have been used providing, for the biepitaxial technique, additional flexibility in circuit design. A detailed investigation on transport properties evidenced good performances for both junctions and superconducting quantum interference devices. Experimental evidence is given of a conventional magnetic field behavior in 45° tilt Artificial Grain Boundary (AGB) for which no π-loops are predicted along the interface.

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