On Frequencies of Occurrence of Geometrically Characteristic Grain Boundaries

2013 ◽  
Vol 203-204 ◽  
pp. 427-430 ◽  
Author(s):  
Krzysztof Glowinski
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Data ◽  
Imaging Techniques ◽  
Serial Sectioning ◽  
Boundary Parameter ◽  
Statistical Studies ◽  
Point Groups ◽  
Twist Boundaries ◽  
Point Of Reference

Development of spatial microstructure imaging techniques (e.g. of automated serial sectioning) has made it possible to collect five macroscopic grain boundary parameters for sets of boundaries large enough for carrying out statistical studies. As a point of reference for future analysis of experimentally measured boundary data, various aspects of estimating the frequencies of occurrence of geometrically characteristic boundaries among random grain boundaries for the cases of cubic Oh, hexagonal D6h and tetragonal D4h point groups are discussed. Example frequencies, in particular for symmetric and improperly quasi-symmetric boundaries, are presented. Two approaches for verification whether a given boundary has a tilt or twist character are confronted, i.e. a method based on a distance function defined in the boundary parameter space and the widely known decomposition of a boundary into its tilt and twist components. The frequencies for tilt and twist boundaries calculated using both methods are compared.

Effect of Grain Boundary Energy Anisotropy on Faceting and Migration of Low Angle Grain Boundaries

2014 ◽  
Vol 783-786 ◽  
pp. 1634-1639
Author(s):  
Dmitri A. Molodov ◽  
Jann Erik Brandenburg ◽  
Luis Antonio Barrales-Mora ◽  
Günter Gottstein
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Elevated Temperatures ◽  
Boundary Energy ◽  
Migration Behavior ◽  
Grain Boundary Energy ◽  
Contrast Imaging ◽  
Orientation Contrast ◽  
And Migration ◽  
Twist Boundaries

The faceting and migration behavior of low angle <100> grain boundaries in high purity aluminum bicrystals was investigated. In-situ technique based on orientation contrast imaging was applied. In contrast to the pure tilt boundaries, which remained straight/flat and immobile during annealing at elevated temperatures, mixed tilt-twist boundaries readily assumed a curved shape and steadily moved under the capillary force. Computational analysis revealed that this behavior is due to the inclinational anisotropy of grain boundary energy, which in turn depends on boundary geometry – the energy of pure tilt low angle <100> boundaries is anisotropic, whereas that of mixed tilt-twist boundaries isotropic with respect to boundary inclination.

The Structure of Dislocations in Low-Angle Grain Boundaries in the Diamond Cubic Lattice

1981 ◽  
Vol 5 ◽  
Author(s):  
C.B. Carter
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Faults ◽  
Burgers Vector ◽  
Cubic Lattice ◽  
Partial Dislocations ◽  
Tilt Boundaries ◽  
P Type ◽  
Twist Boundaries

ABSTRACTDislocations in low-angle tilt boundaries exhibit a wide variety of Burgers vector including a/2<112> a<001> and a<111>. The dislocations are usually dissociated: Shohkley, stair-rod and Frank partial dislocations may each be formed together with associated intrinsic and extrinsic stackingfaults. Dislocations in low-angle {111} twist boundaries are usually assumed to dissociated by a glide mechanism to give two types of extended nodes, known as P–type and K–type, which contain intrinsic and extrinsic stacking-faults respectively. It is shown that dissociation by climb actually occurs for both types of grain boundary.

Observation of grain boundary segregation in advanced ceramics using high-resolution imaging SIMS

1995 ◽  
Vol 53 ◽  
pp. 324-325
Author(s):  
R. Levi-Setti ◽  
K. K. Soni ◽  
J. M. Chabala ◽  
A. M. Thompson
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
High Spatial Resolution ◽  
Imaging Techniques ◽  
Boundary Segregation ◽  
Ion Microprobe ◽  
Broad Beam ◽  
Resolution Imaging ◽  
Boundary Chemistry

The significance of grain boundaries in controlling processing and properties of ceramics is widely acknowledged. Through the addition of suitable dopants to ceramics, their processability and properties can be improved. These dopants may segregate to grain boundaries, but the characterization of boundary chemistry is a challenging task. Studies of segregation phenomena require the application of high-lateralresolution techniques such as STEM/AEM or surface sensitive techniques such as AES, XPS. These techniques require rigorous sample preparation and have their limitations.The scanning ion microprobe is a powerful tool that has exhibited unprecedented potential in the characterization of grain boundaries in ceramics. When interfaced to a mass spectrometer (magnetic sector in our case), this instrument allows mapping of many trace elements at nanometer level in bulk specimens. The combination of excellent sensitivity and high spatial resolution enables direct imaging of grain boundary segregants. The results thus obtained are free from artifacts that typically complicate analysis with broad beam, non-imaging techniques.

Motion of Grain Boundaries: Experiments on Bicrystals

2015 ◽  
Vol 5 ◽  
pp. 247-271
Author(s):  
Dmitri A. Molodov
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Misorientation Angle ◽  
Elevated Temperatures ◽  
Activation Enthalpy ◽  
Boundary Migration ◽  
Boundary Energy ◽  
Boundary Plane ◽  
Migration Behavior ◽  
Twist Boundaries

Recent research on grain boundary migration is reviewed. Novel in-situ measuring techniques based on orientation contrast imaging and the experimental results obtained on specially grown bicrystals are presented. Particularly, the investigated faceting and migration behavior of low angle grain boundaries under the curvature force in aluminum bicrystals was addressed. In contrast to the pure tilt boundaries, which remained straight/flat and immobile during annealing at elevated temperatures, mixed tilt-twist boundaries readily assumed a curved shape and steadily moved under the capillary force. Computational analysis revealed that this behavior is due to the inclinational anisotropy of grain boundary energy, which in turn depends on boundary geometry. The migration of planar grain boundaries induced by a magnetic field was measured in bismuth and zinc bicrystals. Various structurally different boundaries were investigated. The results revealed that grain boundary mobility essentially depends on the misorientation angle and the inclination of the boundary plane. Stress driven boundary migration in aluminium bicrystals was observed to be coupled to a tangential translation of the grains. The activation enthalpy of high angle boundary migration was found to vary non-monotonously with misorientation angle, whereas for low angle boundaries the migration activation enthalpy was virtually the same. The motion of the mixed tilt-twist boundaries under stress was observed to be accompanied by both the translation of adjacent grains parallel to the boundary plane and their rotation around the boundary plane normal.

Correlation between structure, energy, and ideal cleavage fracture for symmetrical grain boundaries in fcc metals

1990 ◽  
Vol 5 (8) ◽  
pp. 1708-1730 ◽  
Author(s):  
D. Wolf
Keyword(s):  
Phase Space ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Cleavage Fracture ◽  
Good Description ◽  
Random Boundary ◽  
Free Surfaces ◽  
Symmetrical Tilt ◽  
Boundary Model ◽  
Twist Boundaries

The misorientation phase space for symmetrical grain boundaries is explored by means of atomistic computer simulations, and the relationship between the tilt and twist boundaries in this three-parameter phase space is clucidated. The so-called random-boundary model (in which the interactions of atoms across the interface are assumed to be entirely random) is further developed to include relaxation of the interplanar spacings away from the grain boundary. This model is shown to include fully relaxed free surfaces naturally, thus permitting a direct comparison of the physical properties of grain boundaries and free surfaces, and hence the determination of ideal cleavage-fracture energies of grain boundaries. An extensive comparison with computer-simulation results for symmetrical tilt and twist boundaries shows that the random-boundary model also provides a good description of the overall structure-energy correlation for both low- and high-angle tilt and twist boundaries. Finally, the role of the interplanar spacing parallel to the grain boundary in both the grain-boundary and cleavage-fracture energies is elucidated.

The behavior of an α-alumina twist grain-boundary in the presence of silica

1990 ◽  
Vol 48 (4) ◽  
pp. 378-379
Author(s):  
Jeffrey G. Maggard ◽  
N. David Theodore ◽  
C. Barry Carter
Keyword(s):  
Mechanical Properties ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Plasma Deposition ◽  
Tetragonal Zirconia ◽  
Ceramic Materials ◽  
Face To Face ◽  
Heating And Cooling ◽  
Optical And Mechanical Properties ◽  
Twist Boundaries

Grain boundaries and polyphase boundaries can control the electrical, optical, and mechanical properties of many ceramic materials. The study of such boundaries is therefore essential for understanding these materials. Some studies of grain boundaries in alumina have reported a thin layer of amorphous intergranular material coating nearly all boundaries while others question this interpretation. The quality and structure (crystalline or amorphous) of an intentionally-added siliceous intergranular phase has been found to affect the mechanical properties of polycrystalline α-alumina and tetragonal zirconia. It is therefore of interest to examine the behavior of various α-alumina grain boundaries in the presence of controlled amounts of amorphous silica. A recent study characterized the behavior of low-angle [0001] twist boundaries in the presence of silica which had been intentionally incorporated during the course of grain boundary fabrication. The present study is aimed at characterizing the behavior of low-angle rhombohedral (102) twist boundaries under similar conditions.Single crystal wafers of α-alumina were mechanically polished parallel to the (102) plane. Silica was deposited to a thickness of 260Å on one of the wafers using plasma deposition. The silica-coated wafers were then placed face-to-face with clean, uncoated wafers and pressure-sintered at 1980°C for 3 hours. The temperature was chosen to lie above the melting point of silica and below that of alumina. A low pressure (∼50 psi) was used to hold the wafers together. The pressure and furnace heating and cooling cycles had to be carefully controlled to prevent fracture of the crystals.

Measurement of the Displacement Across a Coincidence Grain Boundary

1977 ◽  
Vol 35 ◽  
pp. 124-125
Author(s):  
J. W. Matthews ◽  
W. M. Stobbs
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Fault ◽  
The Other ◽  
Measuring Technique ◽  
High Angle ◽  
Twin Boundaries ◽  
Rigid Displacement ◽  
Cubic Crystals ◽  
Lattice Displacement

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

Observations of dislocation interactions with recrystallized grain boundaries

1988 ◽  
Vol 46 ◽  
pp. 628-629
Author(s):  
C. W. Price
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Dislocation Structure ◽  
Hot Deformation ◽  
Static Recrystallization ◽  
High Dislocation Density ◽  
High Angle ◽  
Dislocation Interactions

Little evidence exists on the interaction of individual dislocations with recrystallized grain boundaries, primarily because of the severely overlapping contrast of the high dislocation density usually present during recrystallization. Interesting evidence of such interaction, Fig. 1, was discovered during examination of some old work on the hot deformation of Al-4.64 Cu. The specimen was deformed in a programmable thermomechanical instrument at 527 C and a strain rate of 25 cm/cm/s to a strain of 0.7. Static recrystallization occurred during a post anneal of 23 s also at 527 C. The figure shows evidence of dissociation of a subboundary at an intersection with a recrystallized high-angle grain boundary. At least one set of dislocations appears to be out of contrast in Fig. 1, and a grainboundary precipitate also is visible. Unfortunately, only subgrain sizes were of interest at the time the micrograph was recorded, and no attempt was made to analyze the dislocation structure.

High-resolution x-ray analysis of dislocation networks nn tilt boundaries

1988 ◽  
Vol 46 ◽  
pp. 612-613
Author(s):  
J. R. Michael ◽  
C. H. Lin ◽  
S. L. Sass
Keyword(s):  
Grain Boundaries ◽  
Analytical Electron Microscopy ◽  
Solute Segregation ◽  
X Ray ◽  
Periodic Arrays ◽  
Analytical Electron ◽  
Primary Dislocation ◽  
Tilt Boundaries ◽  
Polycrystalline Solids ◽  
Twist Boundaries

The segregation of solute atoms to grain boundaries in polycrystalline solids can be responsible for embrittlement of the grain boundaries. Although Auger electron spectroscopy (AES) and analytical electron microscopy (AEM) have verified the occurrence of solute segregation to grain boundaries, there has been little experimental evidence concerning the distribution of the solute within the plane of the interface. Sickafus and Sass showed that Au segregation causes a change in the primary dislocation structure of small angle [001] twist boundaries in Fe. The bicrystal specimens used in their work, which contain periodic arrays of dislocations to which Au is segregated, provide an excellent opportunity to study the distribution of Au within the boundary by AEM.The thin film Fe-0.8 at% Au bicrystals (composition determined by Rutherford backscattering spectroscopy), ∼60 nm thick, containing [001] twist boundaries were prepared as described previously. The bicrystals were analyzed in a Vacuum Generators HB-501 AEM with a field emission electron source and a Link Analytical windowless x-ray detector.

Measurement of solute segregation to grain boundaries in the AEM: A review

1988 ◽  
Vol 46 ◽  
pp. 606-607
Author(s):  
D. B. Williams ◽  
A. D. Romig
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Migration ◽  
Grain Boundary Migration ◽  
Boundary Misorientation ◽  
Collector Plate ◽  
Segregation Process ◽  
Grain Boundary Misorientation ◽  
Structure Boundary ◽  
Equilibrium Segregation

The segregation of solute or imparity elements to grain boundaries can occur by three well-defined processes. The first is Gibbsian segregation in which an element of minimal matrix solubility confines itself to a monolayer at the grain boundary. Classical examples include Bi in Cu and S or P in Fe. The second process involves the depletion of excess matrix solute by volume diffusion to the boundary. In the boundary, the solute atoms diffuse rapidly to precipitates, causing them to grow by the ‘collector-plate mechanism.’ Such grain boundary diffusion is thought to initiate “Diffusion-Induced Grain Boundary Migration,” (DIGM). This process has been proposed as the origin of eutectoid transformations or discontinuous grain boundary reactions. The third segregation process is non-equilibrium segregation which result in a solute build-up around the boundary because of solute-vacancy interactions.All of these segregation phenomena usually occur on a sub-micron scale and are often affected by the nature of the grain boundary (misorientation, defect structure, boundary plane).

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