Analytical Electron Microscopy And High-Resolution Electron Microscopy Studies Of Grain-Boundary Films In Silicon Nitride-Based Ceramics

1991 ◽  
Vol 238 ◽  
Author(s):  
H.-J. Kleebe ◽  
M. Rühle
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Film Thickness ◽  
Grain Boundaries ◽  
Liquid Phase Sintering ◽  
Chemical Compositions ◽  
Phase Boundaries ◽  
Intergranular Films ◽  
Boundary Films

ABSTRACTThe microstructures of post-sintered reaction-bonded Si3N4 materials (SRBSN) were investigated. The materials consist of large elongated β-Si3N4 grains embedded in a finegrained matrix. Amorphous secondary phases exist at triple grain junctions owing to the liquid phase sintering involved during densificacition. Those amorphous phases can be crystallized (nearly completely) by post-sintering heat treatment. Apart from these crystalline grain pockets the grains of all materials are covered with thin (<l-2 nm) amorphous intergranular films on both Si3N4/Si3N4 grain boundaries as well as on secondary-phase/Si3N4 phase boundaries. A control of the intergranular films is most desirable since they limit the high-temperature mechanical properties of Si3N4-based ceramics. Therefore, the required characterization was performed by analytical and high-resolution transmission electron microscopy (AEM/HREM). Si3N4 materials with different rare-earth and transition-element oxide additions were studied. AEM and HREM investigations revealed marked differences in thicknesses and chemical compositions of the different intergranular films depending on the system analyzed indicating a strong dependence of film thickness on chemical composition. However, a given composition of each investigated material showed a characteristic intergranular film thickness, independent of grain misorientation, with the only exception of low-energy grain boundaries. The thickness of the intergranular films was constant within 0.2 nm. In addition, the film thickness of phase boundaries was always greater (by 1–2 nm) compared to grain-boundary films.

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.

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.

Grain-Boundary Segregation and Phase-Separation Mechanism in Yttria-Stabilized Tetragonal Zirconia Polycrystal

2011 ◽  
Vol 484 ◽  
pp. 82-88
Author(s):  
Koji Matsui ◽  
Hidehiro Yoshida ◽  
Yuichi Ikuhara
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Segregation ◽  
Grain Boundary Segregation ◽  
Cubic Phase ◽  
Phase Boundaries ◽  
Transmission Electron ◽  
Sintering Condition

Microstructure development during sintering in 3 mol% Y2O3-stabilized tetragonal ZrO2 polycrystal (Y-TZP) was systematically investigated in two sintering conditions: (a) 1100-1650°C for 2 h and (b) 1300°C for 0-50 h. In the sintering condition (a), the density and grain size in Y-TZP increased with the increasing sintering temperature. Scanning transmission electron microscopy (STEM) and nanoprobe X-ray energy dispersive spectroscopy (EDS) measurements revealed that the Y3+ ion distribution was nearly homogeneous up to 1300°C, i.e., most of grains were the tetragonal phase, but cubic-phase regions with high Y3+ ion concentration were clearly formed in grain interiors adjacent to the grain boundaries at 1500°C. High-resolution transmission electron microscopy (HRTEM) and nanoprobe EDS measurements revealed that no amorphous or second phase is present along the grain-boundary faces, and Y3+ ions segregated not only along the tetragonal-tetragonal phase boundaries but also along tetragonal-cubic phase boundaries over a width below about 10 nm, respectively. These results indicate that the cubic-phase regions are formed from the grain boundaries and/or the multiple junctions in which Y3+ ions segregated. We termed this process a “grain boundary segregation-induced phase transformation (GBSIPT)” mechanism. In the sintering condition (b), the density was low and the grain-growth rate was much slow. In the specimen sintered at 1300°C for 50 h, the cubic-phase regions were clearly formed in the grain interiors adjacent to the grain boundaries. This behavior shows that the cubic-phase regions were formed without grain growth, which can be explained by the GBSIPT model.

Grain Boundary Transformations in Bi-Doped Copper

1991 ◽  
Vol 238 ◽  
Author(s):  
Elsie C. Urdaneta ◽  
David E. Luzzi ◽  
Charles J. McMahon
Keyword(s):  
Electron Microscopy ◽  
Heat Treatment ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Treatment Time ◽  
High Resolution Electron Microscopy ◽  
Transmission Electron ◽  
Resolution Electron

ABSTRACTBismuth-induced grain boundary faceting in Cu-12 at ppm Bi polycrystals was studied using transmission electron microscopy (TEM). The population of faceted grain boundaries in samples aged at 600°C was observed to increase with heat treatment time from 15min to 24h; aging for 72h resulted in de-faceting, presumably due to loss of Bi from the specimen. The majority of completely faceted boundaries were found between grains with misorientation Σ=3. About 65% of the facets of these boundaries were found to lie parallel to crystal plane pairs of the type {111}1/{111]2- The significance of these findings in light of recent high resolution electron microscopy experiments is discussed.

Structure of the ∑=3 (111) Grain Boundary in Cu-1.5%Sb

1992 ◽  
Vol 295 ◽  
Author(s):  
Richard W. Fonda ◽  
David E. Luzzi
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Auger Electron ◽  
Preliminary Investigation ◽  
High Resolution Electron Microscopy ◽  
Transmission Electron ◽  
Resolution Electron

AbstractGrain boundaries in quenched and aged Cu-i.5%Sb were examined with Auger electron microscopy, transmission electron microscopy, and high resolution electron microscopy. The ∑=3 grain boundaries are strongly faceted, with the facets lying primarily along the coincident (111) planes of the two grains. The grain boundaries are enriched in antimony, as demonstrated by both AES and HREM. HREM images of the ∑=3 (111) ║ (111) grain boundary differ from those of the Cu-Bi ∑ =3 (111) ║ (111) grain boundary in the lack of a significant grain boundary expansion to accommodate the excess solute at the boundary. A preliminary investigation of the atomic structure of the ∑=3 (111) ║ (111) facet by HREM and multislice calculations is presented.

Anti-Site Bonds and the Structure of Interfaces in SiC

1990 ◽  
Vol 183 ◽  
Author(s):  
P. Pirouz ◽  
J. Yang
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Compound Semiconductors ◽  
High Resolution Electron Microscopy ◽  
High Energy ◽  
Dangling Bonds ◽  
Resolution Electron ◽  
Elemental Semiconductors

AbstractHigh resolution electron microscopy has been used to study the structure of the 3C/6H interface, Σ,=3 {111}and Σ.=3 {112}grain boundaries in 3C-SiC. In SiC, as in other compound semiconductors, anti-site bonds occur in a variety of defects. These are high energy bonds comparable to that of dangling bonds. But, while dangling bonds at the grain boundaries may be eliminated by reconstruction just as in elemental semiconductors, it may not be possible to avoid anti-site bonds.These problems are discussed for the Σ=3 {112} grain boundary, where the structures proposed for Ge and Si are used as starting models for SiC.

Time-resolved high-resolution electron microscopy of grain migration process in MgO films

1996 ◽  
Vol 54 ◽  
pp. 674-675
Author(s):  
T. Kizuka ◽  
M. Iijima ◽  
N. Tanaka
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Migration ◽  
High Resolution Electron Microscopy ◽  
Video Tape ◽  
Grain Boundary Migration ◽  
Time Resolved ◽  
Resolution Electron

High-resolution electron microscopy (HREM) has been employed intensively to analyze the atomic structures of grain boundaries and interfaces having two dimensional structures inside polycrystalline and composite materials. Furthermore time-resolved HREM (TRHREM) is required to analyze the behavior of grain boundaries and interfaces at atomic scale. The grain boundary migration, which is a typical grain boundary behavior, is a fundamental process relating to structural stability of polycrystalline materials. The mechanism of the migration has been still unknown.In the present study, the variation of atomic arrangement at the grain boundary migration of a MgO [001]Σ5 boundary was analyzed by TRHREM.Magnesium oxide polycrystalline films were prepared by vacuum-deposition on air-cleaved (001) surfaces of sodium chloride at 300°C. TRHREM was carried out at room temperature using a 200-kV electron microscope (JEOL, JEM2010) equipped with a high sensitive TV camera and a video tape recorder. The spatial resolution of the system was 0.2 nm at 200 kV and the time resolution was 1/60 s. Electron beam density was 30 A/cm2.

Dislocation - Grain Boundary Interaction in Nickel Bicrystals Evolution of the Resulting Defects under Thermal Treatment

2000 ◽  
Vol 652 ◽  
Author(s):  
Louisette Priester ◽  
Sophie Poulat ◽  
Brigitte Décamps ◽  
Jany Thibault
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Thermal Treatment ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Dislocation Network ◽  
Boundary Interaction ◽  
Transmission Electron

ABSTRACTThe interactions between lattice dislocations and grain boundaries were studied in nickel bicrystals. Three types of grain boundaries, according to their energy, were investigated : singular σ3 {111}, vicinal near σ11 {311} and general near σ11 {332} grain boundaries. The experiments were performed by transmission electron microscopy using a set of techniques : conventional, weak beam, in situ and high resolution transmission electron microscopy. Dislocation transmission from one crystal to the other was only observed for σ3 {111} GB. It consists in a decomposition within the grain boundary of the trapped lattice dislocation followed by the emission of one partial in the neighbouring crystal. A high resolved shear stress is required to promote the emission process. Most often, the absorbed lattice dislocations or extrinsic grain boundary dislocations react with the intrinsic dislocation network giving rise to complex configurations. The evolutions with time and upon thermal treatment of these configurations were followed by in situ transmission electron microscopy. The evolution processes, which differ with the type of grain boundaries, were analyzed by comparison with the existing models for extrinsic grain boundary dislocation accommodation. They were tentatively interpretated on the basis of the grain boundary atomic structures and defects obtained by high resolution transmission electron microscopy studies.

scholarly journals High Resolution Electron Microscopy of Grain Boundaries in Nanophase Palladium

1989 ◽  
Vol 153 ◽  
Author(s):  
G. J. Thomas ◽  
R. W. Siegel ◽  
J. A. Eastman
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Lattice Structure ◽  
High Resolution Electron Microscopy ◽  
Coarse Grained ◽  
Resolution Electron ◽  
The Individual ◽  
Individual Grains

AbstractUsing high resolution electron microscopy, consolidated nanophase palladium samples were examined following electrolytic thinning after a hydriding - dehydriding cycle at 310 K. Due to the small size and random orientations of the individual grains, a large number of grain boundaries were available for examination. Some of these yielded adequate imaging conditions to allow observation of the lattice structure in the grain boundary regions. Image simulations were performed to determine the sensitivity of the technique to lattice disorder. The results of these studies suggest that grain boundary structures in nanophase palladium are similar to those in conventional coarse-grained polycrystals.

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