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Online since: April 2013
Authors: Baya Zebentout, Asmaa Bensmain, Zineb Benamara, Hadjira Tayoub
The benefit of pc-Si is to make devices with large grain size.
The crystallized material is assumed formed by parallel single-crystalline grains, LG sized, separated by physically thick amorphous grain boundaries with a thickness of 1 nm.
Because of the complexity of the structure model and the limited number of points in programming language, only five perpendicular grain boundaries are considered here.
Density of States at the Grain Boundaries.
Also the potential variations are identical from one grain to another grain except the ones near the free surfaces or metal contacts.
Online since: October 2006
Authors: Majid R. Ayatollahi, M.R.M. Aliha, R. Ashtari
Mode I and Mode II Fracture Toughness Testing for a Coarse Grain Marble M.R.M.
A series of fracture toughness tests have been conducted on a type of coarse grain marble.
A total number of 22 CCNBD specimens were tested successfully under mode I conditions.
Specimen Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 KIc , KIIc (MPa m 0.5 ) 1.0 1.5 2.0 2.5 3.0 KIc (Test Data) Average value of KIc KIIc (Test Data) Average value of KIIc Fig. 4: Mode I and mode II fracture toughness of tested CCNBD specimens made of coarse grain marble.
The average value of σt reported for typical coarse grain marble is about 4.7 MPa [14,15].
Online since: April 2005
Authors: Wolfgang Ludwig, Jean Yves Buffière, Emilie Ferrié
Grain Boundary imaging.
Sample geometry Fig. 2. 3D rendering of the crack shape at different numbers of cycles as seen along the stress direction (z direction).
Crack front - grain boundary interaction.
From Fig. 3a, it can be deduced that the crack front geometry is influenced by the different grains in which it propagates : the front seems to propagate faster in grain Y (between points 2 and 3) than in grain Z (between point 1 and 2).
Nielsen and al. : Three-dimensional maps of grain boundaries and the stress state of individual grains in polycrystals and powders.
Online since: February 2007
Authors: Zi Long Tang, Zhong Tai Zhang, Zhi Gang Zhou
The Barium Titanate PTCR phenomenon is a grain-boundary (GB) resistive effect.
But for BaTiO3 PTCR ceramics have been studied only by a limited number of investigators [4-5].
An equivalent circuit consist of intra (grain), inter-grain (grain boundary) and electrode interface regions of a BaTiO3 PTC thermistor which is proposed by Maiti and Basu [6].
Electrical behavior and Grain-boundary potential barrier.
The total resistance of the sample is shown to be composed of at least two, grain boundary (GB) and grain (G), components as shown in Fig. 3.
Online since: December 2010
Authors: Rinat K. Islamgaliev, Marina A. Nikitina, Aidar F. Kamalov
It is recognized that main reasons for grain growth in UFG materials are the enhanced grain boundary energy and high grain boundary mobility [6].
The average grain size D was calculated by the results of diameter measurements of over 100 grains.
According to observations in optical microscope the average grain size in the initial coarse-grained samples after solid solution treatment and water quenching was about of 40 mm.
The stress amplitude as a function of the number of cycles for the АK4-1 processed by combined HPT.
Valiev // In: Ultrafine Grained Materials IV.
Online since: January 2006
Authors: Kazuo Kitagawa, Alexei Vinogradov, V.I. Kopylov
(2) the distribution of grain sizes is rather broad, Fig.3a and b; the average area equivalent grain diameter d* in the flow plane TD of as ECAP-specimens is 0.16±0.04 om with a fairly large population of grains sized having less than 0.1 om dimension.
(3) a large number of low-angle boundaries (LABs) is visible in both OIM and TEM images.
This suggests that a large number of neighboring grains may be involved into crack tip plasticity, even near threshold.
It is therefore, unclear how plastic deformation can be transferred from one grain to the other and how dislocations in neighboring grains can interact with each other.
' The cyclic plastic zone is estimated to be considerably greater than the average grain size, and a possible explanation to this fact is supposed to be given in terms of the effective role played by the non-equilibrium grain boundaries for accommodation and transfer of plastic strain from one grain to the other via specific interface-related mechanisms such as grain boundary sliding.
Online since: September 2013
Authors: Florian Ambrosy, Volker Schulze, Frederik Zanger
Metallic materials used in technical applications are polycrystalline in nature and are composed of a large number of grains which are separated by grain boundaries.
The grain size hereby has an approximately diameter of 1 µm.
The number of intercepts per unit length of the test-line at the grain boundary of the cross-sections can then be used to estimate the grain size.
L is the length of the test-line, z the number of lines, nk the number of intercepts the line makes at the grain boundaries and V the magnification factor of the micrograph. 25 test-lines each with a length of 10 µm are applied for the microstructural analysis.
At rß of 30 µm the grain size in a depth of 1µm is 200 nm, whereas at rß of 150 µm the grain size is 120 nm.
Online since: June 2010
Authors: Patrick S. Grant, Jia Wei Mi, Z. Guo
Thermal shock effectively promoted the fragmentation of the dendritic grains, providing a significant grain multiplication effect to refine the final solidification microstructure.
Compared with large body of work of crystal growth under stable conditions or the additions of various extrinsic grain refiners to promote heterogeneous nucleation, the intrinsic grain refinement due to dendrite fragmentation under more commonly found unsteady conditions are relatively neglected.
The model provides an initial step towards simulating intrinsic grain refining effects under highly transient conditions, and shows thermal pulses are extremely effective in increasing the number of solid particles per unit volume during solidification.
These parameters were chosen arbitrarily to demonstrate the model ability, and clearly a large number of conditions could be explored.
According to Figure 2, more than 200 dendrite fragments were created due to the thermal shock, ~20 times more than the number of the originally seeded crystals, although larger grains remained of approximately constant dimensions since primary dendrite arms were comparatively stable under these particular conditions.
Online since: June 2014
Authors: Daisuke Terada, Nobuhiro Tsuji, Tadashiege Nagae
Ultra-fine grained (UFG) microstructures having mean grain sizes less than 1mm fabricated by the SPD processes exhibit remarkable mechanical properties due to grain refinement hardening.
UFG materials also have large number of other lattice defects introduced by the SPD process.
It was found that the increase in hardness by aging process decreased with increasing the number of the ARB cycles.
In the as-ST or as-ARB specimen (Fig.2(a)), the strength increased with increasing the number of the ARB cycle while elongation decreased by the ARB.
(2) The strength of the ARB processed specimen increased with increasing the number of the ARB process while the elongation decreased by the ARB process.
Online since: July 2007
Authors: Quan Lin Jin, Zhi Peng Zeng, Yan Shu Zhang
In general, the dynamic recrystallization causes grain refinement and stress softening, and the strain induced grain growth causes stress hardening.
Let diffusion creep, grain boundary sliding and dislocation creep are numbered by 1, 2, 3, respectively, and subscript k=1, 2, 3 denotes the variables related with the k-th mechanism, such as fk denotes the volume fraction of the k-th mechanism.
D0, D1, D2, Dc, is initial grain size, unrecrystallized grain size, recrystallized grain size and maximum difference of grain size ,respectively. γ0 is grain boundary energy per unit area of grain boundary.
Fig.8 Un-recrystallized grain D1.
Fig.9 Average grain size D.
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