Early Stages of Carbon Segregation and Precipitation in a Σ = 5 (310)[001] Molybdenum Tilt Boundary

2002 ◽  
Vol 8 (4) ◽  
pp. 305-311 ◽  
Author(s):  
Jean-Michel Pénisson ◽  
Maria Bacia
Keyword(s):  
Electron Microscopy ◽  
High Temperature ◽  
High Resolution ◽  
Grain Boundary ◽  
High Resolution Electron Microscopy ◽  
Tilt Boundary ◽  
Resolution Electron ◽  
Boundary Precipitation ◽  
Grain Boundary Precipitation ◽  
Tilt Grain Boundary

A Σ = 5 (310)[001] tilt grain boundary in molybdenum has been annealed at high temperature in the presence of carbon and observed in high-resolution electron microscopy. The carbon is located at the grain boundary in a 1-nm slab. Two different morphologies coexist. The first one is a grain boundary precipitation while the second one can be considered as a segregation.

Structural Transformation of a Germanium Σ=13 (510) [001] Tilt Grain Boundary under the Electron Beam

1990 ◽  
Vol 48 (1) ◽  
pp. 52-53 ◽  
Author(s):  
Jean-Luc Rouvière ◽  
Alain Bourret
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Structural Transformation ◽  
Mirror Symmetry ◽  
High Resolution Electron Microscopy ◽  
Structural Transformations ◽  
Covalent Bonds ◽  
Resolution Electron ◽  
Tilt Grain Boundary

The possible structural transformations during the sample preparations and the sample observations are important issues in electron microscopy. Several publications of High Resolution Electron Microscopy (HREM) have reported that structural transformations and evaporation of the thin parts of a specimen could happen in the microscope. Diffusion and preferential etchings could also occur during the sample preparation.Here we report a structural transformation of a germanium Σ=13 (510) [001] tilt grain boundary that occurred in a medium-voltage electron microscopy (JEOL 400KV).Among the different (001) tilt grain boundaries whose atomic structures were entirely determined by High Resolution Electron Microscopy (Σ = 5(310), Σ = 13 (320), Σ = 13 (510), Σ = 65 (1130), Σ = 25 (710) and Σ = 41 (910), the Σ = 13 (510) interface is the most interesting. It exhibits two kinds of structures. One of them, the M-structure, has tetracoordinated covalent bonds and is periodic (fig. 1). The other, the U-structure, is also tetracoordinated but is not strictly periodic (fig. 2). It is composed of a periodically repeated constant part that separates variable cores where some atoms can have several stable positions. The M-structure has a mirror glide symmetry. At Scherzer defocus, its HREM images have characteristic groups of three big white dots that are distributed on alternatively facing right and left arcs (fig. 1). The (001) projection of the U-structure has an apparent mirror symmetry, the portions of good coincidence zones (“perfect crystal structure”) regularly separate the variable cores regions (fig. 2).

Atomic Structure of 66° [110] Asymmetric Tilt Grain Boundary in Aluminum

1996 ◽  
Vol 466 ◽  
Author(s):  
M. Shamsuzzoha ◽  
P. A. Deymier ◽  
David J. Smith
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
High Resolution Electron Microscopy ◽  
Structural Features ◽  
Resolution Electron ◽  
Cold Rolling And Annealing ◽  
Line Defects ◽  
Tilt Grain Boundary ◽  
Straight Segments

ABSTRACTA 66° [110] asymmetric tilt grain boundary in Al prepared by cold rolling and annealing has been studied by high-resolution electron microscopy. Due to a 4.5° deviation from the perfect Σ3 misorientation, the boundary is heavily faceted with straight segments running parallel to (111) and (112) planes. All atomic sites across the (111) facets appear to be coincident with the (111) planes at an angle of 66°. The line defects which accommodate the deviation from the perfect twin orientation result in grain boundary stepping. The observed structural features can be described in terms of secondary grain boundary dislocations with Burgers vectors of the type ⅓<111>, and ⅙<112> as well as their interactions.

High-resolution Electron Microscopy Observation of Grain-boundary Films in Superplastically Deformed Silicon Nitride

2000 ◽  
Vol 15 (7) ◽  
pp. 1551-1555 ◽  
Author(s):  
Guo-Dong Zhan ◽  
Mamoru Mitomo ◽  
Yuichi Ikuhara ◽  
Taketo Sakuma
Keyword(s):  
Electron Microscopy ◽  
Silicon Nitride ◽  
High Resolution ◽  
Grain Boundary ◽  
Applied Stress ◽  
Thickness Distribution ◽  
High Resolution Electron Microscopy ◽  
Stress Axis ◽  
Resolution Electron ◽  
Boundary Films

The thickness distribution of grain-boundary films during the superplastic deformation of fine-grained β–silicon nitride was investigated by high-resolution electron microscopy. In particular, grain-boundary thickness was considered with respect to the stress axis in two orientations; namely, parallel and perpendicular to the direction of applied stress. The results showed that the thickness distribution in boundaries perpendicular to the direction of applied stress was unimodal, whereas in parallel boundaries it was bimodal. Moreover, it was found that the majority of film-free boundaries were parallel to the direction of applied stress in the extremely deformed sample. The variation in spacing reflects distribution of stresses within the material due to irregular shape of the grains and the existence of percolating load-bearing paths through the microstructure.

High-Resolution Electron Microscopy Observations of Grain-Boundary Films in Silicon Nitride Ceramics

1992 ◽  
Vol 287 ◽  
Author(s):  
H.-J. Kleebe ◽  
M. K. Cinibulk ◽  
I. Tanaka ◽  
J. Bruley ◽  
R. M. Cannon ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Silicon Nitride ◽  
High Resolution ◽  
Grain Boundary ◽  
Film Thickness ◽  
High Resolution Electron Microscopy ◽  
Resolution Electron ◽  
Nitride Ceramics ◽  
Boundary Films ◽  
Repulsive Forces

ABSTRACTCharacterization of silicon nitride ceramics by transmission electron microscopy (TEM) provides structural and compositional information on intergranular phases necessary to elucidate the factors that can influence the presence and thickness of grain-boundary films. Different TEM techniques can be used for the detection and determination of intergranular-film thickness, however, the most accurate results are obtained by high-resolution electron microscopy (HREM). HREM studies were applied, in conjunction with analytical electron microscopy, to investigate the correlation between intergranular-phase composition and film thickness. Statistical analyses of a number of grain-boundary films provided experimental verification of a theoretical equilibrium film thickness. Model experiments on a high-purity Si3N4 material, doped with low amounts of Ca, suggest the presence of two repulsive forces, a steric force and a force produced by an electrical double layer, that may act to balance the attractive van der Waals force necessary to establish an equilibrium film thickness.

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