scholarly journals Direct observation of individual dislocation interaction processes with grain boundaries

2016 ◽  
Vol 2 (11) ◽  
pp. e1501926 ◽  
Author(s):  
Shun Kondo ◽  
Tasuku Mitsuma ◽  
Naoya Shibata ◽  
Yuichi Ikuhara
Keyword(s):  
Grain Boundaries ◽  
Polycrystalline Materials ◽  
High Angle ◽  
Dislocation Interaction ◽  
Structural Stabilization ◽  
Dislocation Glide ◽  
Transmission Electron ◽  
Dislocation Behavior ◽  
Geometric Effects

In deformation processes, the presence of grain boundaries has a crucial influence on dislocation behavior; these boundaries drastically change the mechanical properties of polycrystalline materials. It has been considered that grain boundaries act as effective barriers for dislocation glide, but the origin of this barrier-like behavior has been a matter of conjecture for many years. We directly observe how the motion of individual dislocations is impeded at well-defined high-angle and low-angle grain boundaries in SrTiO3, via in situ nanoindentation experiments inside a transmission electron microscope. Our in situ observations show that both the high-angle and low-angle grain boundaries impede dislocation glide across them and that the impediment of dislocation glide does not simply originate from the geometric effects; it arises as a result of the local structural stabilization effects at grain boundary cores as well, especially for low-angle grain boundaries. The present findings indicate that simultaneous consideration of both the geometric effects and the stabilization effects is necessary to quantitatively understand the dislocation impediment processes at grain boundaries.

TEM observations of electromagnetically characterized YBa2Cu3O7-x grain boundaries in flux-grown bicrystals

1991 ◽  
Vol 49 ◽  
pp. 1072-1073
Author(s):  
S.E. Babcock ◽  
N. Zhang
Keyword(s):  
Grain Boundaries ◽  
Large Scale ◽  
Three Dimensional ◽  
Electromagnetic Properties ◽  
Polycrystalline Materials ◽  
High Angle ◽  
Pinning Mechanism ◽  
Transmission Electron ◽  
Bulk Scale ◽  
Microscopy Techniques

The original thin-film bicrystal studies strongly indicated that all high-angle grain boundaries in YBa2Cu3O7-x are intrinsically weak-linked and exhibit Josephson junction characteristics. More recent investigations of individual grain boundaries in both bulk-scale bicrystals and textured thin films have shown that the Jct properties of high-angle grain boundaries can vary in important ways. Specifically, high-angle grain boundaries with Jct behavior characteristic of a flux pinning mechanism have been discovered. These results are encouraging from the view point of large-scale applications. However, further engineering of polycrystalline materials can first be conducted in a deliberate way when the microstructural origin of the observed behaviors is understood in detail.In these studies, light and transmission electron microscopy techniques are used to investigate the microstructure of the very same bulk bicrystalline samples whose electromagnetic properties have been characterized. The three-dimensional macroscopic features of the grain boundary are deduced from light microscopy observations as the entire bicrystal is mechanically ground and polished to approximately 20 microns in thickness.

On In-Situ Study of Dislocation/Grain Boundary Interactions Using X-ray Topography and Tem

1993 ◽  
Vol 319 ◽  
Author(s):  
Ian Baker ◽  
Fuping Liu
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stress Concentrations ◽  
X Ray ◽  
Advantages And Disadvantages ◽  
Transmission Electron ◽  
Low Dislocation Density ◽  
Dislocation Behavior ◽  
Generation Mechanisms

AbstractThe advantages and disadvantages of in-situ straining using both synchrotron x-ray topography and transmission electron microscopy for examining dislocation/grain boundary interactions are compared and examples given of the use of each technique. For x-ray topography, studies on ice polycrystals are discussed. Ice is well-suited for x-ray topographic studies since it has both low absorption and can be produced with a low dislocation density. Stress concentrations have been observed at grain boundaries in ice which are partially relieved by generation of 1/3<1120> dislocations. Interestingly, grain boundary generation of dislocations completely overwhelms lattice generation mechanisms. Examples of transmission electron microscope in-situ straining studies include dislocation/grain boundary interactions in L12-structured and B2-structured intermetallics. Slip transmission across grain boundaries by dislocations gliding ahead of an advancing crack is a principal feature of these studies. A significant advantage of the such studies is their inherently high resolution. However, the dislocation behavior is dominated by the inherent thinness of the specimens.

scholarly journals Defect mastering - one of the topic challenges for crystal growth

2014 ◽  
Vol 70 (a1) ◽  
pp. C32-C32
Author(s):  
Peter Rudolph
Keyword(s):  
Crystal Growth ◽  
Grain Boundaries ◽  
Point Defect ◽  
Dislocation Dynamics ◽  
Cell Diameter ◽  
Second Phase ◽  
Dislocation Loops ◽  
Misfit Stress ◽  
Dislocation Interaction

The quality of single crystals, epitaxial layers and devices made there from are very sensitively influenced by structural and atomistic deficiencies generated during the crystal growth. Crystalline imperfections comprise point defects, dislocations, grain boundaries, second-phase particles. Over more than a half-century of the development of crystal growth, most of the important defect-forming mechanisms have become well understood [1-2]. As a result, the present state of technology makes it possible to produce crystals of remarkably high quality. However, that is not to say that all problems are already solved. For instance, in comparison with silicon the point defect dynamics in semiconductor and oxide compounds is not nearly as well understood. The density of equivalent defect types and antisites in each sub-lattice is determined by deviation from stoichiometry. Their charge state depends on the Fermi level position leading via interaction with dopants to certain compensation level and complex formation. One measure proves to be the in situ control of stoichiometry. Due to high-temperature dislocation dynamics heterogeneous dislocation substructures are formed. Both, acting thermo-mechanical stress and given point defect situation force the dislocation to glide and climb. In the course of enthalpy minimization the long-range character of dislocation interaction produces agglomerates and patterns with polygonized cell walls, i.e. small angle grain boundaries [3]. Thanks to the rules of correspondence of Taylor and Kuhlmann-Wilsdorf one is able to estimate the interaction between shear stress, dislocation density and cell diameter (Fig.). In epitaxy the Nye tensor, describing dislocation distribution inhomogeneity, affects the layer stress considerably. The growth under minimum stress, solution hardening and in situ stoichiometry control are effective counteracting methods. One of the most serious consequences during cooling down of as-grown crystals is the point defect condensation in precipitates and micro-voids decorating dislocation patterns or inducing high mechanical misfit stress that generates dislocation loops. It proves to be favourable to anneal the crystal a few degrees below the melting point in order to dissolve the particles and re-diffuse their into the crystal matrix.

Observations and implications of grain boundary dislocation networks in high-angle YBa2Cu3O7−δ grain boundaries

1990 ◽  
Vol 5 (5) ◽  
pp. 919-928 ◽  
Author(s):  
S. E. Babcock ◽  
D. C. Larbalestier
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Weak Link ◽  
Coincidence Site Lattice ◽  
Boundary Structure ◽  
High Angle ◽  
Grain Boundary Structure ◽  
Transmission Electron ◽  
Means Of Transmission ◽  
Regular Networks

Regular networks of localized grain boundary dislocations (GBDs) have been imaged by means of transmission electron microscopy in three different types of high-angle grain boundaries in YBa2Cu3O7-δ, implying that these boundaries possess ordered structures upon which a significant periodic strain field is superimposed. The occurrence of these GBD networks is shown to be consistent with the GBD/Structural Unit and Coincidence Site Lattice (CSL)/Near CSL descriptions for grain boundary structure. Thus, these dislocations appear to be intrinsic features of the boundary structure. The spacing of the observed GBDs ranged from ∼10 nm to ∼100 nm. These GBDs make the grain boundaries heterogeneous on a scale that approaches the coherence length and may contribute to their weak-link character by producing the “superconducting micro-bridge” microstructure which has been suggested on the basis of detailed electromagnetic measurements on similar samples.

The Effect of Grain Boundaries on Surface Diffusion Mediated-Planarization of Polycrystalline Cu Films

1995 ◽  
Vol 389 ◽  
Author(s):  
R.A. Brain ◽  
D.S. Gardner ◽  
D.B. Fraser ◽  
H.A. Atwater
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Surface Diffusion ◽  
Cross Sections ◽  
Boundary Surface ◽  
Surface Profile ◽  
Transmission Electron Micrograph ◽  
Cu Films ◽  
Transmission Electron

ABSTRACTIn situ, ultrahigh vacuum anneals were performed to induce Cu reflow at 500°C following deposition of Cu films and a Ta barrier layer on 1 μm wide by 1 μm deep trenches. Transmission electron micrograph cross-sections show profiles which suggest that grain boundaries and surface energy anisotropy significantly affect reflow. The extent of reflow is dependent on the structure of grain boundary-surface intersections, and the surface profile consists of regions of low curvature within grains and with sharp discontinuities in curvature at grain boundaries, a structure that inhibits surface diffusion. We present results showing how the surface diffusion mediated reflow varies with grain boundary groove angle and position, and compare these results with finite-element simulations that model surface diffusion-driven reflow.

Effect of boron on the mechanism of strain transfer across grain boundaries in Ni3Al

1987 ◽  
Vol 2 (4) ◽  
pp. 436-440 ◽  
Author(s):  
G. M. Bond ◽  
I. M. Robertson ◽  
H. K. Birnbaum
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Dislocation Motion ◽  
Strain Transfer ◽  
Undoped Material ◽  
Sudden Failure ◽  
Transmission Electron ◽  
Large Numbers ◽  
Dislocation Sources

The effect of boron on the mechanism of strain transfer across grain boundaries in Ni3Al has been investigated by dynamic recording of events occurring during in-situ straining in the transmission electron microscope. Boundaries in both doped and undoped material can act as effective barriers to dislocation motion, large numbers of dislocations being incorporated into the boundary without any plastic strain occurring in the adjacent grain. In the undoped material, the grain-boundary strain is relieved by the sudden failure of the grain boundary. In the doped material the strain is relieved by the sudden generation and emission of large numbers of dislocations from the grain boundary. This effect may be understood by boron either increasing the grain-boundary cohesion or reducing the stress required to operate grain-boundary dislocation sources, rather than easing the passage of slip dislocations through the grain boundary.

Indentation-Induced Deformation Behavior in Martensitic Steel Observed through In Situ Nanoindentation in a Transmission Electron Microscopy

2006 ◽  
Vol 503-504 ◽  
pp. 239-244 ◽  
Author(s):  
Takahito Ohmura ◽  
A. Minor ◽  
Kaneaki Tsuzaki ◽  
J.W. Morris
Keyword(s):  
Grain Boundary ◽  
Deformation Behavior ◽  
Critical Stress ◽  
Martensitic Steel ◽  
High Angle ◽  
Block Boundary ◽  
Density Of Dislocations ◽  
Transmission Electron ◽  
Pile Up

Deformation behavior in the vicinity of grain boundary in Fe-0.4wt%C tempered martensitic steel were studied through in-situ nanoindentation in a TEM. Two types of boundaries were imaged in the dislocated martensitic structure: a low-angle lath boundary and a high-angle block boundary. In the case of a low-angle grain boundary, the dislocations induced by the indenter piled up against the boundary. As the indenter penetrated further, a critical stress appears to have been reached and a high density of dislocations was suddenly emitted on the far side of the grain boundary into the adjacent grain. In the case of the high-angle grain boundary, the numerous dislocations that were produced by the indentation were simply absorbed into the boundary, with no indication of pile-up or the transmission of strain.

Evaluation of X-ray Bragg peak profiles with the variance method obtained by in situ measurement on Mg–Al alloys

2020 ◽  
Vol 53 (2) ◽  
pp. 360-368
Author(s):  
Gergely Farkas ◽  
István Groma ◽  
Jozef Veselý ◽  
Kristián Máthis
Keyword(s):  
Dislocation Density ◽  
Profile Analysis ◽  
Line Profile Analysis ◽  
Dislocation Interaction ◽  
X Ray ◽  
Variance Method ◽  
Al Content ◽  
Transmission Electron ◽  
Bragg Peak Profiles

The microstructural evolution in randomly oriented Mg–Al samples is investigated in situ during compression by X-ray diffraction as a function of Al concentration. The diffraction data are evaluated by the variance method, which provides information about the dislocation density and spatial distribution of the dislocations. The dislocation density increases with increasing alloying content. Since the increment of the dislocation density above the yield point is linear, the mutual dislocation interaction type is determined from the Taylor equation. The results indicate the dominance of basal–basal dislocation interactions, but at higher alloying content the share of the basal–non-basal interactions increases. It is shown that the dynamics of dislocation wall formation also depend on Al content. Transmission electron microscopy observations are in agreement with the results obtained by X-ray line profile analysis.

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