scholarly journals Молекулярно-динамическое исследование влияния концентрации вакансий на скорость миграции границ наклона в никеле

2021 ◽  
Vol 63 (5) ◽  
pp. 582
Author(s):  
Г.М. Полетаев ◽  
Р.Ю. Ракитин
Keyword(s):  
Free Volume ◽  
Driving Force ◽  
Migration Rate ◽  
Vacancy Concentration ◽  
High Angle ◽  
Vacancy Clusters ◽  
Method Of Molecular Dynamics ◽  
Initial Stage ◽  
Tilt Boundaries ◽  
Mobile Vacancy

The influence of vacancy concentration on the migration rate of high-angle tilt boundaries with misorientation axes <111> and <100> in nickel was studied by the method of molecular dynamics. It is shown that the dependence of the migration rate on the concentration of vacancies introduced at the initial stage of modeling has a maximum near 1%. The decrease in the migration rate with a further increase in the free volume is mainly due to the deceleration of the boundary by low-mobile vacancy clusters, which at high vacancy concentrations the boundary is no longer capable of sorbing. The second reason for the decrease in the migration rate with an increase in the concentration of vacancies above 1% is a decrease in the surface tension of grain boundaries and, accordingly, the driving force of their migration due to the finite sorption capacity of the boundaries with respect to the excess free volume.

scholarly journals Влияние концентрации вакансий на скорость миграции границ наклона в никеле: молекулярно-динамическое моделирование

2021 ◽  
Vol 47 (8) ◽  
pp. 29
Author(s):  
Г.М. Полетаев ◽  
Р.Ю. Ракитин
Keyword(s):  
Molecular Dynamics ◽  
Grain Boundaries ◽  
Migration Rate ◽  
Vacancy Concentration ◽  
High Angle ◽  
Vacancy Clusters ◽  
Method Of Molecular Dynamics ◽  
Initial Stage ◽  
Tilt Boundaries ◽  
Small Clusters

The effect of vacancy concentration on the migration rate of high-angle tilt boundaries with misorientation axes <111> and <100> in nickel was studied by the method of molecular dynamics. It is shown that the dependence of the migration rate of grain boundaries on the vacancy concentration is nonmonotonic and has a maximum at a concentration of vacancies introduced at the initial stage of about 1%. With a further increase in concentration, especially above 4%, the migration rate of the considered boundaries decreased as a result of deceleration of boundaries by low-mobility vacancy clusters attached to it, which the boundary could no longer sorb, as in the case of relatively small clusters.

Excess Free Volume of High Angle Grain Boundaries in Aluminium

2006 ◽  
Vol 519-521 ◽  
pp. 1557-1562 ◽  
Author(s):  
V.A. Ivanov ◽  
Dmitri A. Molodov ◽  
Lasar S. Shvindlerman ◽  
Günter Gottstein ◽  
D. Kolesnikov ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Free Volume ◽  
Pressure Range ◽  
Boundary Energy ◽  
Tilt Boundary ◽  
Triple Junctions ◽  
High Angle ◽  
Absolute Value ◽  
Excess Free Volume ◽  
Tilt Boundaries

A new method is introduced to determine the absolute value of the boundary excess free volume. Along with the boundary energy the excess free volume belongs to the major thermodynamic properties of grain boundaries. The method utilizes the dependence of the contact angle at triple junctions of grain boundaries in Al-tricrystals on hydrostatic pressure. We investigated <111> tilt boundaries in the pressure range up to 14 kbar. In particular, for a 40° <111> tilt boundary with 2° twist component the boundary free volume was found to be equal to 5.03×10-11 m3/m2.

scholarly journals Molecular dynamics study of the influence of uniaxial deformation on the migration velocity of tilt boundaries in nickel

2021 ◽  
Vol 2131 (4) ◽  
pp. 042052
Author(s):  
G M Poletaev ◽  
D I Ziuzin ◽  
D V Novoselova ◽  
R Y Rakitin
Keyword(s):  
Molecular Dynamics ◽  
Surface Tension ◽  
Free Space ◽  
Driving Force ◽  
Migration Velocity ◽  
Uniaxial Deformation ◽  
High Angle ◽  
Tilt Boundaries ◽  
Almost All ◽  
Dynamics Method

Abstract The molecular dynamics method was used to study the influence of elastic uniaxial deformation on the migration velocity of tilt boundaries with misorientation axes [100] and [111] in nickel. The dependences of the migration velocity at a temperature of 1600 K on the misorientation angle were obtained. It is shown that the high-angle [100] and [111] tilt boundaries migrate at approximately the same velocity, while the low-angle [111] boundaries migrate approximately twice as fast as the [100] boundaries. The obtained dependences of the migration velocity of the boundaries on the value of uniaxial deformation in almost all cases turned out to be nonmonotonic and had a maximum at a tension value of about 1%. With a further increase in tension, migration slowed down, which is most likely explained by a decrease in the surface tension of the boundaries and, accordingly, in the driving force due to the finite sorption capacity of grain boundaries with respect to the free volume. Under elastic compression, in most cases, a monotonic decrease in the migration velocity was observed, which is due to a decrease in free space during compression and a decrease in the mobility of atoms at the boundary.

scholarly journals Positive selection alone is sufficient for whole genome differentiation at the early stage of speciation process in the fall armyworm

2019 ◽  
Author(s):  
Kiwoong NAM ◽  
Sandra Nhim ◽  
Stéphanie Robin ◽  
Anthony Bretaudeau ◽  
Nicolas Nègre ◽  
...  
Keyword(s):  
Positive Selection ◽  
Driving Force ◽  
Migration Rate ◽  
Early Stage ◽  
Fall Armyworm ◽  
Whole Genome ◽  
Low Level ◽  
Evolutionary Forces ◽  
Genome Differentiation ◽  
Genetic Linkages

Abstract Background: The process of speciation inherently involves the transition from genetic to genomic differentiation. In the absence of a geographic barrier, the whole genome differentiation may occur only when the homogenizing effect of recombination is overcome across the whole genome. The fall armyworm is observed as two sympatric strains with different host-plant preferences across the entire habitat. These two strains exhibit a very low level of genetic differentiation across the whole genome, suggesting that whole genome differentiation occurred at an early stage of speciation. In this study, we aim at identifying critical evolutionary forces responsible for the whole genome differentiation in the fall armyworm. Results: We found that these two strains exhibit a low level of genomic differentiation (Fst = 0.0176), while 91.3% of 10kb windows have genetically differentiated sequences (Fst > 0). We observed that a genomic reduction in migration rate due to combined effects of mild positive selection and genetic linkages to selectively targeted loci are responsible for the whole genome differentiation. Phylogenetic analysis shows that positive selection generates the whole genome differentiation by sub-setting of variants in one strain from the other. Conclusions: From these results, we concluded that positive selection alone is sufficient for whole genome differentiation during the process of speciation. This study demonstrates that the propensity of adaptation alone determines the speciation events, suggesting that adaptive evolution is a single critical driving force for species diversity.

Optical Studies of Deep Centers in Semi-Insulating SiC

2006 ◽  
Vol 527-529 ◽  
pp. 455-460 ◽  
Author(s):  
Björn Magnusson ◽  
Reino Aavikko ◽  
Kimmo Saarinen ◽  
Nguyen Tien Son ◽  
Erik Janzén
Keyword(s):  
Vacancy Concentration ◽  
Point Of View ◽  
Optical Studies ◽  
Intrinsic Defects ◽  
Vacancy Clusters ◽  
Silicon Vacancy ◽  
Deep Centers ◽  
Metal Impurities ◽  
Insulating Properties ◽  
Absorption Measurements

Semi-insulating SiC grown by the HTCVD technique are studied by luminescence and absorption measurements and the results are compared to PAS and SIMS results. We have found that metal impurities are present but only in very small concentrations. The semi-insulating properties are instead determined by the intrinsic defects, mostly the silicon vacancy in hydrocarbon rich grown material and the carbon vacancy in the hydrocarbon poor grown material. The hydrocarbon poor material is stable upon annealing both from a vacancy concentration point of view and from a resistivity point of view. The hydrocarbon rich grown material does not stand the annealing at 1600 °C and the resistivity is decreased; from the absorption and PAS measurements we have observed that the decrease in silicon vacancy concentration fits the growth of the vacancy clusters.

Coherency Strain Energy in any Crystal System: Applications to in Situ Observations of Cigm in Calcite

1990 ◽  
Vol 205 ◽  
Author(s):  
R.S. May ◽  
B. Evans
Keyword(s):  
Driving Force ◽  
Migration Rate ◽  
Strain Energy ◽  
Solute Concentration ◽  
Coherency Strain ◽  
Solute Diffusion ◽  
Boundary Orientation ◽  
In Situ Observations ◽  
And Migration

AbstractIn situ observations of CIGM in CaCO3 bicrystals with a SrCO3 solute source were made. The change in boundary orientation and migration rate were compared with solute concentration. The liquid film model for coherency strain Induced migration was generalized to any non-cubic system and applied to CaCO3-SrCO3. The coherent layer was modeled as a thin film on an infinite half-space. The strain energy was found from solution of the Hooke's law expressions transformed to the appropriate coordinate system. For triclinic or monoclinic films the strain tensor was found by an eigenvector decomposition of the transformation matrix that defined the lattice parameter change with composition. High anisotropy of Vegard's law constants for CaCO3-SrCO3 caused (111) to have the lowest coherency strain per unit solute. Surfaces perpendicular to (111) in coherent equilibria were predicted to have half the solute concentration and three times the migration driving force of those perpendicular to (111). However, no correlation between solute concentration and boundary orientation was observed. Ambiguous and contradictory evidence for a relationship between solute concentration, boundary orientation, and migration rate was found. The self-stress state of a grain boundary in a solute diffusion field may be better modelled as hydrostatic rather than plane stress. Hydrostatic compression may interact with the boundary excess volume and cause a PV driving force for migration. Predictions based on coherent equilibrium at a surface have not been tested for that geometry in calcite; they should be tested before they are applied to grain boundaries.

Atomistic Aspects of Crack Propagation Along High Angle Grain Boundaries

1996 ◽  
Vol 460 ◽  
Author(s):  
Diana Farkas
Keyword(s):  
Grain Boundary ◽  
Atomistic Simulations ◽  
High Angle ◽  
Brittle Behavior ◽  
Embedded Atom ◽  
Tilt Boundaries ◽  
Symmetrical Tilt ◽  
Grain Boundary Fracture ◽  
Tilt Grain Boundary ◽  
Boundary Fracture

ABSTRACTWe present atomistic simulations of the crack tip configuration near a high angle Σ= 5 [001](210) symmetrical tilt grain boundary in NiAl. The simulations were carried out using molecular statics and embedded atom (EAM) potentials. The cracks are stabilized near a Griffith condition involving the cohesive energy of the grain boundary. The atomistic configurations of the tip region are different in the presence of the high angle grain boundary than in the bulk. Three different configurations of the grain boundary were studied corresponding to different local compositions. It was found that in ordered NiAl, cracks along symmetrical tilt boundaries show a more brittle behavior for Al rich boundaries than for Ni-rich boundaries. Lattice trapping effects in grain boundary fracture were found to be more significant than in the bulk.

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