Morphological Changes in Rod-Shaped Precipitates With Internal Boundaries: Finite Difference Analysis

1991 ◽  
Vol 237 ◽  
Author(s):  
Jun-Ho Choy ◽  
S. A. Hackney ◽  
J. K. Lee
Keyword(s):  
Aspect Ratio ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Morphological Changes ◽  
Equilibrium Shape ◽  
Interfacial Free Energy ◽  
Dynamic State ◽  
Shape Evolution ◽  
Boundary Groove ◽  
The Relationship

ABSTRACTShape evolution of rod-shaped precipitates due to surface diffusion has been studied under the conditions of constant volume and isotropie interfacial free energy. The shape evolution depends strongly on both the initial aspect ratio and the grain boundary groove angle. For a finite rod with one grain boundary, the morphology evolves into an equilibrium shape made of spherical portions if its aspect ratio and the groove angle are small. Increase in the aspect ratio causes a boundary splitting. For an infinite rod with periodic boundaries, three types of morphological evolutions are observed. When the relationship between the aspect ratio and the groove angle satisfies a certain critical condition, the shape evolves into an equilibrium. If the relationship deviates significantly from this condition, an ovulation process takes place at each location of the internal grain boundaries. When the deviation is intermediate, the morphology undergoes an oscillation in a quasi-dynamic state between the process toward an equilibrium shape and the ovulation process. The ovulation process due to internal grain boundaries is found to precede the Rayleigh spheroidization process.

scholarly journals Numerical Analysis and Experimental Study on Fabrication of High Aspect Ratio Tapered Ultrafine Holes by Over-Growth Electroforming Process

Micromachines ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 824
Author(s):  
Yunyan Zhang ◽  
Pingmei Ming ◽  
Runqing Li ◽  
Ge Qin ◽  
Xinmin Zhang ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Structural Parameters ◽  
Geometric Shape ◽  
High Tech ◽  
Shape Evolution ◽  
Metallic Plate ◽  
Electroforming Process ◽  
Photoresist Film ◽  
The Relationship

High aspect ratio (HAR) ultrafine tapered holes (diameter ≤5 μm; AR ≥5) are the most important elements for some high-tech perforated metallic products, but they are very difficult to manufacture. Therefore, this paper proposes a nontraditional over-growth electroforming process. The formation mechanism of the HAR ultrafine tapered holes is investigated, and the factors controlling the geometric shape evolution are analyzed numerically. It was found that the geometric shape and dimensions of the holes are highly dependent on the diameter and thickness of the photoresist film patterns, but are hardly affected by the spacing between two neighboring patterns; the achievable diameter for a given hole depth becomes small with the increasing pattern diameter, but it becomes big with the increasing pattern thickness. These correlations can be well interpreted by the established two empirical equations that characterize the relationship between the minimum orifice of the tapered hole and the structural parameters of the photoresist film patterns previously formed on the substrate. Application of the fabricated 1500 tapered holes with 3-μm diameter and 17-AR as the nozzles of the medical precision nebulizer is also examined. The studies show that the over-growth electroforming process is highly applicable in fabricating the perforated metallic plate with HAR ultrafine tapered holes.

Grain-Boundary Energy and Grain-Boundary Groove Angles in Ice

1972 ◽  
Vol 11 (62) ◽  
pp. 265-277 ◽  
Author(s):  
Shigenao Suzuki ◽  
Daisuke Kuroiwa
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Energy ◽  
Grain Boundary Energy ◽  
Boundary Groove ◽  
Grain Boundary Grooves

Abstract Relative grain-boundary energies in ice were measured as a function of mismatch angles made by the c-axes or a-axes in grains, using ice specimens having triple grain boundaries. It was found that the Read–Shockley equation for grain-boundary energy was valid for grain boundaries tilted between 0° and 15°. Angles of the solid–vapour grain-boundary groove in ice were measured by the use of micro-interferometry at grain-boundary grooves covered with extremely thin metalic foil. The data were compared with those measured by a silvered replica of grain-boundary grooves.

Effects of Microstructures on the Mechanical Properties of Dilute Al-Si Alloys

2007 ◽  
Vol 345-346 ◽  
pp. 821-824
Author(s):  
Keiyu Nakagawa ◽  
Teruto Kanadani
Keyword(s):  
Fatigue Strength ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Aging Time ◽  
Fracture Elongation ◽  
Micro Cracks ◽  
Hand Fracture ◽  
Stress Cycles ◽  
Effects Of Aging ◽  
The Relationship

In this paper, we investigated effects of aging at 473K on the relationship between microstructure in the vicinity of the grain boundaries and fatigue strength for Al-1.2%Si alloy. Results obtained show the following features. (1) As aging time, tA increase, the tensile strength (σB) and 0.2% proof stress (σ0.2) increase slowly, but gradually decrease after reaching a maximum at around 18 ks. On the other hand, fracture elongation shows an opposite trend, suggesting that at aging times above 18ks, over aging occurs. (2) The fatigue strength lowers with increasing aging time, however, when the aging time is more than 18 ks at 473K, the fatigue strength remains almost the same. (3) When the aging time is more than 6 ks, grain boundary precipitates with a size greater than several 10s of nm are observed. (4) When the aging time is 18 ks, an accumulation of dislocations are observed at the grain boundaries and in the vicinity of grain boundary precipitates, and dislocations increase with the number of stress cycles. (5) When the aging time is more than 6 ks, the fatigue fracture surface is mainly intergranular. These results suggest that reduction of fatigue strength results from propagation of micro-cracks which are initiated at the large precipitates on the grain boundaries.

Study of Bonding of Grain Boundaries in Steels Using EELS

2005 ◽  
Vol 475-479 ◽  
pp. 4063-4066
Author(s):  
X. Zhang ◽  
Lina Zhang ◽  
Jun Jie Qi ◽  
Yue Ma
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Fracture Mode ◽  
Fracture Property ◽  
Transgranular Fracture ◽  
The Difference ◽  
Relationship Of ◽  
The Relationship

A novel EELS technique was developed to study bonding of grain boundary in many kinds of steels. We measured the normalized intensities of Fe white lines and calculated the occupancies of 3d states of iron, and then analyzed the relationship of the occupancies of 3d states of iron and the fracture property of the steels. We found that if the grain boundary has a different occupancy of 3d state of iron from that of the bulk, the steel tends to have an intergranular fracture, whereas if the grain boundary has almost the same occupancy of 3d state as the bulk, the steel tends to have a transgranular fracture. Our result shows that the difference in the occupancy of 3d state between bulk and grain boundary can be used to study the fracture mode at grain boundary in steel.

Equilibrium Shapes of Pb Inclusions at 90° Tilt Grain Boundaries in Al

1996 ◽  
Vol 54 ◽  
pp. 364-365
Author(s):  
E. Johnson ◽  
U. Dahmen ◽  
S.-Q. Xiao ◽  
A. Johansen
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Nearest Neighbor ◽  
Lattice Mismatch ◽  
Equilibrium Shape ◽  
Minimum Energy ◽  
Aluminum Matrix ◽  
Spherical Cap ◽  
Polycrystalline Aluminum ◽  
Aluminum Films

Ion implantation of lead in aluminum leads to spontaneous phase separation and formation of dense distributions of nanosized lead inclusions[1]. The inclusions have fee structure, and despite the large lattice mismatch (aA1 = 0.4048 nm and aPb = 0.495 nm) they grow in parallel-cube topotaxy with the matrix. Their shape is cuboctahedral with larger {111} facets and smaller {100} facets which is the minimum- energy shape for an fee crystal in equilibrium with its vapor, as calculated by considering only nearest neighbor bonds. Implantation of polycrystalline aluminum films is accompanied by preferential nucle- ation and enhanced growth of inclusions in the grain boundaries. In adapting their equilibrium shape, grain boundary inclusions will be subject to a larger number of constraints than inclusions in the bulk matrix. This may result in a variety of morphologies characteristic for different types of grain boundaries.In the present study we have used a well-defined bicrystal geometry to study the morphology and structure of lead grain boundary inclusions in mazed bicrystal aluminum films containing mainly 90°<110> tilt boundaries with fixed misorientation but variable inclination[2]. It was found that the shape, size and orientation of the inclusions in the grain boundaries depend on the inclination, i.e. the orientation of the grain boundary plane. Inclusions were all single crystalline and invariably faceted toward one aluminum grain and more rounded toward the other grain (fig.l). Independent of grain boundary inclination, the faceted side was a section of the cuboctahedral equilibrium shape of inclusions in parallel topotaxy with the bulk aluminum matrix. The rounded side, where the inclusions were rotated by 90° with respect to the aluminum lattice, approximated a spherical cap consisting partly of somewhat flatter segments with complex faceting, illustrating the lack of distinctly flat low-energy facets.

Wetting Transitions of Grain Boundaries

1999 ◽  
Vol 586 ◽  
Author(s):  
John Blendell
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Abrupt Change ◽  
Equilibrium Shape ◽  
Second Phase ◽  
Curved Surfaces ◽  
Wetting Layer ◽  
Wetting Transitions ◽  
Microscopic Morphology ◽  
Morphology Changes

ABSTRACTIt has been shown that the concepts used to determine the equilibrium shape of crystals can be extended to determine the conditions under which grain boundaries will be fully wetted, partially wetted, or not wetted by a second phase. Recent experimental observations on the equilibrated morphologies of solid or fluid wetting phases along grain boundaries, reveal features that are predicted, and in some cases required, by this construction. Theory distinguishes between cases where surfaces are smoothly curved or where there are facets, edges and corners. In the latter case the conventional comparison of the energy of the original grain boundary with the sum of the surface energy of the two surfaces of the wetting layer leads to erroneous predictions. The correct predictions are obtained by comparing the Wulff shape of the grain boundary (the interfacial energy minimizing shape for a fixed volume of material) with a carefully defined sum of Wulff shapes of the surfaces of the wetting layer. Where orientations that are wetted join with those that are not, there is almost always an abrupt change of orientation. Faceting on two hierarchical levels can occur. Microscopic morphology changes along macroscopically curved surfaces follow well defined rules predicted by theory. The analogy between the thermodynamics of interface faceting and phase transformations allows the well known concepts of phase equilibria to be used to understand the predicted structures. The predictions of the model will be used to identify the nature of the faceting observed in alumina in the presence of a second phase.

scholarly journals Molecular dynamics investigation on tilt grain boundary energies of beta-titanium and tungsten at high temperature

2021 ◽  
Author(s):  
Hong He ◽  
Shangyi Ma ◽  
Shaoqing Wang
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Dynamic Simulations ◽  
Beta Titanium ◽  
Symmetric Tilt ◽  
Higher Temperature ◽  
Lattice Misorientation ◽  
The Relationship ◽  
Variation Trends

Abstract The grain boundary energies (GBEs) of symmetric tilt grain boundaries (STGBs) and asymmetric tilt grain boundaries (ATGBs) for W at 0 and 2400 K and β-Ti at 1300 K were calculated by means of Molecular static method and Molecular dynamic simulations to investigate the effects of high temperature and grain boundary (GB) planes on the GBE. Generally, the variation trends of GBEs functioned with tilt angle are similar in the three cases when the tilt axis is specified. It is of course that these similarities result from their similar GB microstructures in most cases. However, the variation trends of β-Ti at 1300 K are somewhat different from that of W at 2400 K for STGBs with <100> and <110> tilt axes. This difference mainly stems from the following two reasons: firstly, the GB microstructures of W at 2400 K and β-Ti at 1300 K are different for some STGBs; secondly, the atoms at STGB of β-Ti at 1300 K tend to evolve into the local ω- or α-like structures distributed at STGBs, which make the corresponding STGBs more stable, thereby decreasing the GBEs. Furthermore, a geometric parameter θ, an angle between misorientation axis and GB plane, was defined to explore the effects of GB planes on GBEs. It was found that the relationship between GBEs and sin(θ) can be described by some simple functions of sin(θ) for the GBs with definite lattice misorientation, which can well explain and predict the preferred GB planes for the GBs with specific lattice misorientation. Our calculations not only extend the investigation of GBs to higher temperature, but also deepen the understanding on the temperature contribution to the microstructure evolution at GBs and on the relationship between GBE and possible geometric parameters.

The Role of Transmission Electron Microscopy in Characterizing the Nature and Behavior of Grain Boundaries

1971 ◽  
Vol 29 ◽  
pp. 102-103
Author(s):  
L. E. Murr
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Degrees Of Freedom ◽  
Effective Means ◽  
Average Energy ◽  
Interfacial Free Energy ◽  
Transmission Electron ◽  
And Behavior

Grain boundaries represent the single, most dominant imperfection in structural materials of engineering and industrial importance, and are a controlling factor in the strength of materials. Transmission electron microscopy, combined with the ability to gain direct crystallographic information from associated selected-area electron diffraction patterns, represents perhaps the most effective means for the investigation of the nature and behavior of grain boundaries in solids.Any segment of a grain boundary has associated with it five degrees of freedom. The electron microscope has the capability to characterize these degrees of freedom and to uniquely define the geometrical and crystallographic nature of a grain boundary. In addition, once the true geometry of intersecting grain boundaries or grain boundaries intersecting with other interfaces is determined, interfacial free energy ratios can be calculated from which the average energy associated with particular types of interfaces can be determined.

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