Role of Interfaces in Coarsening and Grain Growth

1991 ◽  
Vol 229 ◽  
Author(s):  
S. P. Marsh ◽  
M. E. Glicksman
Keyword(s):  
Grain Growth ◽  
Mean Field ◽  
Three Dimensional ◽  
Liquid Phase Sintering ◽  
Global Constraints ◽  
Material Interfaces ◽  
Wide Range ◽  
The Matrix ◽  
Field Approaches

AbstractTheories of late-stage phase separation are discussed from the perspective of statistical mean-field approaches, whereby the material interfaces are assumed to interact with the appropriate average microstructural environment. For coarsening of two- and three-dimensional phases, recent progress is presented for selecting the most appropriate averages that characterize the microstructural environment surrounding a domain. The effective mean field, as well as the average interaction distance over which transport occurs, may be determined self-consistently by imposing global constraints that reflect the microstructural phase fractions and by using explicit spatial and ensemble averages of the matrix transport fields. Comparison of new theoretical coarsening rates with liquid-phase sintering experiments show good agreement over a wide range of phase fractions. Extension of this approach to grain growth, which involves more complex topological interactions, is also discussed.

Conditions for the Occurrence of Abnormal Grain Growth Studied by a 3 D Vertex Dynamics Model

2012 ◽  
Vol 715-716 ◽  
pp. 563-567 ◽  
Author(s):  
M. Syha ◽  
D. Weygand
Keyword(s):  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Energy ◽  
Mean Field ◽  
Three Dimensional ◽  
Abnormal Grain Growth ◽  
Dynamics Model ◽  
Boundary Properties ◽  
The Impact ◽  
Field Approaches

The conditions for the nucleation of abnormal grain growth were investigated using a three dimensional vertex dynamics model. Potentially abnormal growing grains characterized by their size and topological class, respectively and embedded in an isotropic grain ensemble were subjected to annealing varying their grain boundary properties. The simulation results indicate that the classical mean field approaches underestimate the role of the grain boundary energy advantage, while the impact of a mobility advantage is overestimated.

Three Dimensional Monte Carlo Simulations with Real Grain Orientations for the Role of Sub-Boundaries and Precipitates in Abnormal Grain Growth

2013 ◽  
Vol 753 ◽  
pp. 367-372
Author(s):  
Tae Wook Na ◽  
Chang Soo Park ◽  
Hyung Seok Shim ◽  
Byeong Joo Lee ◽  
Chan Hee Han ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Solid State ◽  
Monte Carlo Simulations ◽  
Grain Growth ◽  
Three Dimensional ◽  
Abnormal Grain Growth ◽  
Grain Orientations ◽  
The Matrix ◽  
Simulation Results

Three-dimensional Monte Carlo simulations with real grain orientations are performed to study the role of precipitates and sub-boundaries in the abnormal grain growth. According to the simulation results, sub-boundaries in the abnormally growing grain and precipitates in the matrix grains are necessary for the abnormal grain growth. The simulation results can be best explained by the mechanism of sub-boundary enhanced solid state wetting. The simulated microstructure is very similar to that experimentally observed.

Microstructure of Polycrystalline MgO Penetrated by a Silicate Liquid

1996 ◽  
Vol 2 (3) ◽  
pp. 113-128 ◽  
Author(s):  
Sundar Ramamurthy ◽  
Michael P. Mallamaci ◽  
Catherine M. Zimmerman ◽  
C. Barry Carter ◽  
Peter R. Duncombe ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Glassy Phase ◽  
Silicate Liquid ◽  
Two Phase ◽  
The Matrix ◽  
Devitrification Process ◽  
Phase Mixture

Dense, polycrystalline MgO was infiltrated with monticellite (CaMgSiO4) liquid to study the penetration of liquid along the grain boundaries of MgO. Grain growth was found to be restricted with increasing amounts of liquid. The inter-granular regions were generally found to be comprised of a two-phase mixture: crystalline monticellite and a glassy phase rich in the impurities present in the starting MgO material. MgO grains act as seeding agents for the crystallization of monticellite. The location and composition of the glassy phase with respect to the MgO grains emphasizes the role of intergranular liquid during the devitrification process in “snowplowing” impurities present in the matrix.

scholarly journals Dynamics of Orographically Triggered Banded Convection in Sheared Moist Orographic Flows

2007 ◽  
Vol 64 (10) ◽  
pp. 3542-3561 ◽  
Author(s):  
Oliver Fuhrer ◽  
Christoph Schär
Keyword(s):  
Small Amplitude ◽  
Three Dimensional ◽  
Horizontal Resolution ◽  
Small Scale ◽  
Mean Flow ◽  
Topographic Roughness ◽  
Wide Range ◽  
Orographic Convection ◽  
Wind Profiles

Abstract Shallow orographic convection embedded in an unstable cap cloud can organize into convective bands. Previous research has highlighted the important role of small-amplitude topographic variations in triggering and organizing banded convection. Here, the underlying dynamical mechanisms are systematically investigated by conducting three-dimensional simulations of moist flows past a two-dimensional mountain ridge using a cloud-resolving numerical model. Most simulations address a sheared environment to account for the observed wind profiles. Results confirm that small-amplitude topographic variations can enhance the development of embedded convection and anchor quasi-stationary convective bands to a fixed location in space. The resulting precipitation patterns exhibit tremendous spatial variability, since regions receiving heavy rainfall can be only kilometers away from regions receiving little or no rain. In addition, the presence of banded convection has important repercussions on the area-mean precipitation amounts. For the experimental setup here, the gravity wave response to small-amplitude topographic variations close to the upstream edge of the cap cloud (which is forced by the larger-scale topography) is found to be the dominant triggering mechanism. Small-scale variations in the underlying topography are found to force the location and spacing of convective bands over a wide range of scales. Further, a self-sufficient mode of unsteady banded convection is investigated that does not dependent on external perturbations and is able to propagate against the mean flow. Finally, the sensitivity of model simulations of banded convection with respect to horizontal computational resolution is investigated. Consistent with predictions from a linear stability analysis, convective bands of increasingly smaller scales are favored as the horizontal resolution is increased. However, small-amplitude topographic roughness is found to trigger banded convection and to control the spacing and location of the resulting bands. Thereby, the robustness of numerical simulations with respect to an increase in horizontal resolution is increased in the presence of topographic variations.

Diversity of the sponge fauna associated with white coral banks from two Sardinian canyons (Mediterranean Sea)

2019 ◽  
Vol 99 (8) ◽  
pp. 1735-1751 ◽  
Author(s):  
M. Bertolino ◽  
S. Ricci ◽  
S. Canese ◽  
A. Cau ◽  
G. Bavestrello ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Cold Water ◽  
Three Dimensional ◽  
Western Mediterranean ◽  
Tyrrhenian Sea ◽  
Lophelia Pertusa ◽  
Wide Range ◽  
Santa Maria

AbstractThe three-dimensional coral scaffolds formed by the skeletons of the cold-water corals Madrepora oculata and Lophelia pertusa represent an important deep-sea hard substratum and create an optimal shelter for a rich associated fauna in which the contribution of Porifera has still not been fully considered. The taxonomic analysis of sponges collected from two Sardinian canyons (Nora and Coda Cavallo, 256–408 m) and associated with the dead coral matrix resulted in 28 species, including new records for the Mediterranean Sea, Italian fauna or Central Tyrrhenian Sea. In addition, for many species this is the first finding associated with the coral framework or the first documentation of the in situ morphology. The taxonomic comparison with sponge assemblages associated with coral frameworks from Santa Maria di Leuca, Strait of Sicily and Bari Canyon, gave the opportunity to evaluate the similarities among geographically separated banks. Overall, the percentage of exclusive species (recorded only in one site), is very high (81%) and only one species is shared by all four sites, suggesting a low connectivity among the sponge communities. The percentage of shared species is higher for the Maltese community, supporting the role of the Sicily Channel as a crossroads between the communities of the eastern and western Mediterranean basins. Here, 55% of the sponges associated to the coral framework are also reported in shallow-water coralligenous assemblages, indicating a high bathymetric connectivity as well as an ecological plasticity allowing these species to occupy a wide range of small, dark refuges.

scholarly journals 6D electron microscopy: combining real-space and reciprocal-space tomography

2014 ◽  
Vol 70 (a1) ◽  
pp. C368-C368 ◽  
Author(s):  
Alexander Eggeman ◽  
Robert Krakow ◽  
Paul Midgley
Keyword(s):  
Reciprocal Lattice ◽  
Three Dimensional ◽  
Real Space ◽  
Dark Field ◽  
Reciprocal Space ◽  
Data Set ◽  
Wide Range ◽  
The Matrix ◽  
Precession Electron Diffraction ◽  
Tilt Series

STEM and TEM-based tomography has been used widely to study the 3D morphology of a wide range of materials. Similarly reciprocal space tomography in which a tilt-series of diffraction patterns are acquired offers a powerful method for the analysis of the atomic structure of crystalline materials. The natural progression is to combine these techniques into a complete three dimensional morphology and crystallography data set, allowing both features to be studied simultaneously. Using a tilt series of scanning precession electron diffraction measurements from a commercially available Ni-base superalloy as an example, the complete reciprocal lattice orientation for a number of components embedded within the matrix could be determined. It was straightforward to identify reciprocal lattice vectors that allowed dark-field images representing each phase to be produced post-acquisition. In turn these were combined using geometric tomography methods to yield a 3-D tomogram of the superalloy. Imaging these phases using conventional ADF STEM tomography would potentially be challenging given the compositional similarity between the different phases. From the combined dataset the spatial distribution of the component phases could be easily recovered but more importantly the orientational relationships between these different components could be unambiguously determined. In this way the thermo-mechanical history of the sample could be inferred from the arrangement of coherent and semi-coherent interfaces and a previously unreported crystallographic registry between metal carbide (MC) and the matrix f.c.c. phases could been identified. The possibilities for development and applications of this technique will be discussed further.

Monte Carlo Potts Model Simulation and Statistical Theory of 3D Grain Growth

2007 ◽  
Vol 558-559 ◽  
pp. 1219-1224 ◽  
Author(s):  
Dana Zöllner ◽  
Peter Streitenberger
Keyword(s):  
Grain Size ◽  
Monte Carlo ◽  
Grain Growth ◽  
Potts Model ◽  
Model Simulation ◽  
Mean Field Theory ◽  
Mean Field ◽  
Three Dimensional ◽  
Rate Of Change ◽  
Volumetric Rate

An improved Monte Carlo (MC) Potts model algorithm has been implemented allowing an extensive simulation of three-dimensional (3D) normal grain growth. It is shown that the simulated microstructure reaches a quasi-stationary state, where the growth of grains can be described by an average self-similar volumetric rate of change, which depends only on the relative grain size. Based on a quadratic approximation of the volumetric rate of change a generalized analytic mean-field theory yields a scaled grain size distribution function that is in excellent agreement with the simulation results.

Preparation, characterization, and sinterability of well-defined silica/yttria powders

1994 ◽  
Vol 9 (2) ◽  
pp. 436-450 ◽  
Author(s):  
Herbert Giesche ◽  
Egon Matijević
Keyword(s):  
Particle Size ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Grain Growth ◽  
Spherical Particles ◽  
Sintering Process ◽  
Mixed Composition ◽  
Coated Particles ◽  
Wide Range ◽  
The Matrix

Dispersions of uniform submicron spherical particles consisting of silica cores and yttria coatings, or vice versa, were prepared by a precipitation technique. The overall size of the particles and the thickness of the shells could be varied over a wide range. Such powders were used to form green bodies by sedimentation, centrifugation, or pressure filtration, and the density and the pore size distribution of the resulting solids were evaluated. The green bodies were sintered and the changes in density, phases, and microstructure were followed with temperature. In general, the coated powders exhibited enhanced densification. On processing composite solids at temperatures <1000 °C, the formation of Y2Si2O7 took place, which caused a pronounced shrinkage of the samples. Powders of coated particles having the same silica/yttria ratios sintered at lower temperatures when the shell was composed of silica rather than of yttria. When either silica or yttria were in molar excess in the coated particles, the sintered products had a mixed composition of Y2Si2O7 and the component in excess. By terminating the sintering process before the grain growth started, the solids displayed a well-defined microstructure with a uniform distribution of areas of one phase in the matrix of the matter in excess. This property was mainly due to the uniformity of initial powders in terms of the particle size and the coating.

scholarly journals A wrinkle in flight: the role of elastin fibres in the mechanical behaviour of bat wing membranes

2015 ◽  
Vol 12 (106) ◽  
pp. 20141286 ◽  
Author(s):  
Jorn A. Cheney ◽  
Nicolai Konow ◽  
Andrew Bearnot ◽  
Sharon M. Swartz
Keyword(s):  
Mechanical Behaviour ◽  
High Stress ◽  
Three Dimensional ◽  
Wing Membrane ◽  
Surrounding Matrix ◽  
The Matrix ◽  
Mechanical Element ◽  
Bat Wing ◽  
Surrounding Membrane

Bats fly using a thin wing membrane composed of compliant, anisotropic skin. Wing membrane skin deforms dramatically as bats fly, and its three-dimensional configurations depend, in large part, on the mechanical behaviour of the tissue. Large, macroscopic elastin fibres are an unusual mechanical element found in the skin of bat wings. We characterize the fibre orientation and demonstrate that elastin fibres are responsible for the distinctive wrinkles in the surrounding membrane matrix. Uniaxial mechanical testing of the wing membrane, both parallel and perpendicular to elastin fibres, is used to distinguish the contribution of elastin and the surrounding matrix to the overall membrane mechanical behaviour. We find that the matrix is isotropic within the plane of the membrane and responsible for bearing load at high stress; elastin fibres are responsible for membrane anisotropy and only contribute substantially to load bearing at very low stress. The architecture of elastin fibres provides the extreme extensibility and self-folding/self-packing of the wing membrane skin. We relate these findings to flight with membrane wings and discuss the aeromechanical significance of elastin fibre pre-stress, membrane excess length, and how these parameters may aid bats in resisting gusts and preventing membrane flutter.

scholarly journals Experimental study of the three-dimensional flow structure in matrix channels

2021 ◽  
Vol 2057 (1) ◽  
pp. 012027
Author(s):  
M V Philippov ◽  
I A Chokhar ◽  
A V Zolotukhin ◽  
A V Barsukov ◽  
V V Terekhov ◽  
...  
Keyword(s):  
Experimental Study ◽  
Three Dimensional ◽  
Decisive Role ◽  
Three Dimensional Flow ◽  
Matrix Channel ◽  
Dimensional Flow ◽  
The Matrix ◽  
Role Based ◽  
High Degree

Abstract The article presents an experimental study of the turbulent flow in matrix channels. Using the modern optical contactless laser Doppler anemometer (LDA) method, an idea of the turbulent three-dimensional flow inside the cells of matrix channels is developed. The results of the study of the matrix channel show that the so-called vortex matrix effect is not formed. The most important factor that causes a high degree of heat transfer from the walls is the intense spiral motion between the matrix cells. The measurements also show that the effects associated with the lateral boundaries of the channel play a significant role. Based on the assumption of the decisive role of the spiral flow between the cells of the matrix channel, a formula for the integral pressure loss is proposed.

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