Grain Boundary Structure and Sliding of Alumina Bicrystals

1999 ◽  
Vol 601 ◽  
Author(s):  
Y. Ikuhara ◽  
T. Watanabe ◽  
T. Yarnamoto ◽  
T. Saito ◽  
H. Yoshida ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Small Angle ◽  
Boundary Energy ◽  
High Resolution Electron Microscopy ◽  
Grain Boundary Sliding ◽  
Boundary Structure ◽  
Grain Boundary Energy ◽  
Grain Boundary Structure ◽  
Boundary Sliding

AbstractAlumina bicrystals were fabricated by a hot joining technique at 1500°C in air to obtain ten kinds of [0001] symmetric tilt grain boundaries which included small angle, CSL and high angle grain boundaries. Their grain boundary structures were investigated by high-resolution electron microscopy (HREM), and the respective grain boundary energies were systematically measured by a thermal grooving technique. It was found that grain boundary energy strongly depended on the grain boundary characters, e.g., there were large energy cusps at low Σ CSL grain boundaries. But, main part of grain boundary energy is likely to be due to the strain energy around the grain boundary, and the contribution of atomic configuration is not so large. Small angle grain boundaries were consisted of an array of partial dislocation with Burgers vector of 1/3[1100] to form the stacking faults between the dislocations. The behavior of grain boundary sliding was also investigated for typical grain boundaries by high-temperature creep test at 1400°C. As the result, the occurrence of grain boundary sliding was found to depend on the grain boundary atomic structure.

Computer simulation on surfaces and [001] symmetric tilt grain boundaries in Ni, Al, and Ni3Al

1989 ◽  
Vol 4 (1) ◽  
pp. 62-77 ◽  
Author(s):  
S. P. Chen ◽  
D. J. Srolovitz ◽  
A. F. Voter
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Structural Unit ◽  
Boundary Energy ◽  
Boundary Structure ◽  
Grain Boundary Energy ◽  
Local Composition ◽  
Embedded Atom ◽  
Grain Boundary Structure ◽  
Unit Model

We have used “local volume” (embedded atom) type potentials to study the surfaces and grain boundaries of Ni, Al, and Ni3Al. The simulations show that with appropriately fit potentials, the surface and grain boundary structure can be realistically calculated. The surface rippling and relaxation show good agreement with experiments. The energies of most surfaces and grain boundaries also agree with existing data. The structural unit model for grain boundaries in Ni3Al shows the same generic units as in pure metals, but with large variations due to distortions and multiplicity. The utility of the structural unit model is thus more limited for alloys. The grain boundary energies were found to be the highest for Al-rich Ni3Al grain boundaries, and depend significantly on the local composition of the grain boundary. The cusps in the grain boundary energy as a function of misorientation angle are different for different grain boundary stoichiometries. The Ni3Al grain boundaries have approximately the same grain boundary energy and cohesive energy as that of Ni.

High-temperature grain boundary sliding behavior and grain boundary energy in cubic zirconia bicrystals

2004 ◽  
Vol 52 (8) ◽  
pp. 2349-2357 ◽  
Author(s):  
Hidehiro Yoshida ◽  
Kenji Yokoyama ◽  
Naoya Shibata ◽  
Yuichi Ikuhara ◽  
Taketo Sakuma
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Boundary Energy ◽  
Grain Boundary Sliding ◽  
Grain Boundary Energy ◽  
Cubic Zirconia ◽  
Boundary Sliding

Preferred inclinations of grain boundaries in epitaxially grown bicrystalline thin films of gold

1978 ◽  
Vol 36 (1) ◽  
pp. 434-435
Author(s):  
F. Cosandey ◽  
Y. Komem ◽  
C. L. Bauer
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Energy ◽  
Boundary Plane ◽  
Boundary Structure ◽  
Structural Elements ◽  
Grain Boundary Energy ◽  
Transmission Electron ◽  
A New Technique ◽  
Misorientation Of Grains

Energy and concomitant structure of grain boundaries are related to inclination of the boundary plane as well as misorientation of grains defining the boundary. Although increasing information is becoming available on variation of grain boundary energy with misorientation, still relatively little is known about variation of grain boundary energy with inclination. The purpose of this research is to examine preferred inclinations of preselected grain boundaries in gold by transmission electron microscopy (TEM) in order to identify principal structural elements and to relate these elements to the energy of special grain boundary configurations.Grain boundaries examined in this research are produced by a new technique involving vapor deposition of gold on common (001) surfaces of bicrystalline substrates of NaCl, characterized by preselected rotation about a common [001] axis, and subsequent epitaxial growth to form a bicrystalline thin film. These films are then removed from their substrates and examined by TEM. The principal advantage of this technique is that the grain boundary is formed during the deposition and growth process, thus resulting in a more perfect boundary structure while eliminating necessity of a separate bonding operation.

Structure of Grain Boundaries in Metals and Alloys: Direct Observations in the TEM

1973 ◽  
Vol 31 ◽  
pp. 106-107
Author(s):  
L. E. Murr
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Small Angle ◽  
Structural Features ◽  
Metals And Alloys ◽  
Boundary Structure ◽  
Screw Dislocations ◽  
Direct Observations ◽  
Grain Boundary Structure

Many models of grain boundaries in metals and alloys have been developed in attempts to interpret their properties and observed structures. Because of the complexity of grain boundary structure, it is generally possible to apply any of the proposed models in any material, and to describe grain boundaries as possessing dislocation structures, ledges, protrusions, island structures, facets, coincidence regions which exhibit good atomic fit and establish a kind of superlattice array, and combinations of these structural features.The dislocation nature of small angle grain boundaries is well known, consisting of tilt or twist arrays or combinations of edge or screw dislocations.

Effect of Solid-Solution W Addition on the Nanostructure of Electrodeposited Ni

2002 ◽  
Vol 740 ◽  
Author(s):  
Hajime Iwasaki ◽  
Kenji Higashi ◽  
T. G. Nieh
Keyword(s):  
Solid Solution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Nanocrystalline Structure ◽  
Grain Morphology ◽  
Atomic Layer ◽  
High Resolution Electron Microscopy ◽  
Dark Field ◽  
Boundary Structure ◽  
Grain Boundary Structure

ABSTRACTElectrodeposition method was employed to produce freestanding Ni-W alloy foils. The foils consist of nanograins. The structure of the foil, e.g. texture, grain morphology, size distribution, and the nature of grain boundaries, were characterized using X-ray diffraction and high-resolution electron microscopy. The deposited foils exhibit an equiaxed nanocrystalline structure having a grain size value of about 6 nm. Two types of grain boundary structure were observed. One type of grain boundary is essentially one atomic layer thin and another type consists of a structureless layer of about 0.5–1 nm in thickness. Angular dark field (Z-contrast) image of the deposited foils showed an inhomogeneous distribution of W solutes. In some local regions, the W content actually exceeds the equilibrium solid solution limit. Many grain boundaries with a structureless layer of about 0.5–1 nm are probably a result of local supersaturation of W.

Effect of Cu and Al Substitutions on the Microstructure of R-Fe-B Magnets

1991 ◽  
Vol 232 ◽  
Author(s):  
Y. J. Zhang ◽  
L. Withanawasam ◽  
G. C. Hadjipanayis ◽  
A. Kim
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Secondary Phases ◽  
Al Substitution ◽  
Grain Boundary Structure ◽  
Resolution Electron ◽  
Melt Spun

ABSTRACTThe coercivity of melt-spun Pr-Fe-B ribbons was found to increase with the addition of Cu and Al. The change in size and shape of grains with Cu and Al substitution were investigated by transmission eletron microscopy (TEM) and the grain boundary structure was further examined with high resolution electron microscopy (HREM). For small substitutions only “disturbed lattice” regions were observed at most of the grain boundaries. Secondary phases rich in the added elements were observed mostly at tripple grain boundaries and sometimes at grain boundaries in samples with larger amounts of substitution. The grain size in the substituted samples does not decrease much with further substitution. However, the shape of grains changes from polyhexagons to facets. The enhancement in coercivity can be explained by the grain size reduction and the modification of microstructure at the grain boundary regions.

The Influence of Grain Boundary Structure on Strain-Induced Grain Growth During Superplastic Deformation

1990 ◽  
Vol 196 ◽  
Author(s):  
H. J. Frost ◽  
R. Raj
Keyword(s):  
Grain Boundary ◽  
Grain Growth ◽  
Superplastic Deformation ◽  
Boundary Migration ◽  
Forced Migration ◽  
Grain Boundary Sliding ◽  
Boundary Structure ◽  
Grain Boundary Structure ◽  
Diffusional Flow ◽  
Boundary Sliding

ABSTRACTA model is presented to explain the grain growth that is often observed during superplastic deformation. The atomic structure of grain boundaries leads to a coupling between boundary sliding and boundary migration. There is a similar coupling between the absorption or emission of vacancies from a boundary and boundary migration. Because of these couplings, the grain boundary sliding and diffusional flow of superplastic deformation produce extensive boundary migration. We propose that this forced migration leads to random changes in the sizes of grains, and that this evolution of the grain size distribution leads to grain growth.

Finding the Right Problems: Some HREM Applications to Interfaces

1984 ◽  
Vol 42 ◽  
pp. 376-379
Author(s):  
D. Cherns
Keyword(s):  
Grain Boundaries ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Atomic Structures ◽  
Grain Boundary Structure ◽  
Resolution Electron ◽  
Point To Point ◽  
The Right ◽  
New Generation ◽  
Better Than

The use of high resolution electron microscopy (HREM) to determine the atomic structure of grain boundaries and interfaces is a topic of great current interest. Grain boundary structure has been considered for many years as central to an understanding of the mechanical and transport properties of materials. Some more recent attention has focussed on the atomic structures of metalsemiconductor interfaces which are believed to control electrical properties of contacts. The atomic structures of interfaces in semiconductor or metal multilayers is an area of growing interest for understanding the unusual electrical or mechanical properties which these new materials possess. However, although the point-to-point resolutions of currently available HREMs, ∼2-3Å, appear sufficient to solve many of these problems, few atomic models of grain boundaries and interfaces have been derived. Moreover, with a new generation of 300-400kV instruments promising resolutions in the 1.6-2.0 Å range, and resolutions better than 1.5Å expected from specialist instruments, it is an appropriate time to consider the usefulness of HREM for interface studies.

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