Atomistic Simulation of Mobile Defect Clusters in Metals

1998 ◽  
Vol 540 ◽  
Author(s):  
Yu.N. Osetsky ◽  
D.J. Bacon ◽  
A. Serra
Keyword(s):  
Stacking Fault ◽  
Atomic Scale ◽  
Dynamics Simulation ◽  
Structure Stability ◽  
Dislocation Loops ◽  
Fcc Metals ◽  
Thermally Activated ◽  
Vacancy Loops ◽  
Mobile Defect ◽  
The Difference

AbstractThe structure, stability and thermally-activated motion of interstitial and vacancy clusters in Fe and Cu have been studied using atomic scale computer simulation. All studied interstitial clusters and perfect interstitial loops (PILs) in Fe are mobile whereas their mobility in Cu can be suppressed at large sizes (bigger than 49–61 self-interstitials depending on the temperature) due to dissociation. A comparative study of relaxed configurations has shown that the structure of small perfect dislocation loops of vacancy and self-interstitial nature is very similar. Molecular dynamics simulation has demonstrated that small perfect vacancy loops (PVLs) in Fe consisting of more than 37 vacancies are stable over a wide temperature range and produce atomic displacements by a thermally-activated movement in the direction of the Burgers vector. The mechanism is qualitatively similar to that of SIA clusters studied earlier. Motion of vacancy loops in Cu does not occur because they transform into sessile configurations similar to stacking fault tetrahedra. These results point to the possibly important contribution of vacancy loop mobility to the difference in radiation damage between bcc and fcc metals, and between fcc metals with different stacking fault energy.

Atomistic Simulation of Mobile Defect Clusters in Metals

1998 ◽  
Vol 538 ◽  
Author(s):  
Yu.N. Osetsky ◽  
D.J. Bacon ◽  
A. Serra
Keyword(s):  
Stacking Fault ◽  
Atomic Scale ◽  
Dynamics Simulation ◽  
Structure Stability ◽  
Dislocation Loops ◽  
Fcc Metals ◽  
Thermally Activated ◽  
Vacancy Loops ◽  
Mobile Defect ◽  
The Difference

AbstractThe structure, stability and thermally-activated motion of interstitial and vacancy clusters in Fe and Cu have been studied using atomic scale computer simulation. All studied interstitial clusters and perfect interstitial loops (PILs) in Fe are mobile whereas their mobility in Cu can be suppressed at large sizes (bigger than 49-61 self-interstitials depending on the temperature) due to dissociation. A comparative study of relaxed configurations has shown that the structure of small perfect dislocation loops of vacancy and self-interstitial nature is very similar. Molecular dynamics simulation has demonstrated that small perfect vacancy loops (PVLs) in Fe consisting of more than 37 vacancies are stable over a wide temperature range and produce atomic displacements by a thermally-activated movement in the direction of the Burgers vector. The mechanism is qualitatively similar to that of SIA clusters studied earlier. Motion of vacancy loops in Cu does not occur because they transform into sessile configurations similar to stacking fault tetrahedra. These results point to the possibly important contribution of vacancy loop mobility to the difference in radiation damage between bcc and fcc metals, and between fcc metals with different stacking fault energy.

Grain Refinement of High-Purity FCC Metals Using Equal-Channel Angular Pressing

2007 ◽  
Vol 558-559 ◽  
pp. 1273-1278 ◽  
Author(s):  
Z. Horita ◽  
Kaoru Kishikawa ◽  
Keiichi Kimura ◽  
Kohei Tatsumi ◽  
Terence G. Langdon
Keyword(s):  
Equal Channel Angular Pressing ◽  
High Purity ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Grain Refining ◽  
Fcc Metals ◽  
Angular Pressing ◽  
The Difference ◽  
Pure Cu ◽  
Very High

Equal-channel angular pressing (ECAP) is a valuable technique for refining grain sizes to the submicrometer or the nanometer range. This study explores the reason for the difference in the grain refining behavior between pure Al and pure Cu. First, very high purity levels were adopted in order to minimize any effects of impurities: 99.999% for Al and 99.99999% for Cu. Second, high purity (99.999%) Au was also used in order to examine the effect of stacking fault energy. All three pure metals were subjected to ECAP and microstructural observations and hardness measurements were undertaken with respect to the number of ECAP passes. It is concluded that the stacking fault energy plays an important role and accounts for the difference in the grain refining behavior in the ECAP process.

Molecular Dynamics Simulations to Evaluate the Effect of the Difference in Material Properties on Irradiation-Induced Defect Formation Under Applied Strain

2012 ◽  
Author(s):  
Toshihiro Horinouchi ◽  
Satoshi Miyashiro ◽  
Mitsuhiro Itakura ◽  
Taira Okita
Keyword(s):  
Molecular Dynamics ◽  
Defect Formation ◽  
Stacking Fault ◽  
Applied Strain ◽  
Stacking Fault Energy ◽  
Cascade Process ◽  
Defect Production ◽  
Fcc Metals ◽  
The Difference ◽  
Dynamics Simulations

The influence of applied strain on the defect production rate during a cascade process was evaluated for several FCC metals with different Stacking Fault Energy by the method of molecular dynamics. It was found that applied strain increases the number of surviving defects, which is caused by the enhanced formation of larger clusters. It was also found that the number of defects is almost independent of Stacking Fault Energy even under applied strain.

scholarly journals Micromechanics of Void Nucleation and Early Growth at Incoherent Precipitates: Lattice-Trapped and Dislocation-Mediated Delamination Modes

Crystals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 45
Author(s):  
Qian Qian Zhao ◽  
Brad L. Boyce ◽  
Ryan B. Sills
Keyword(s):  
Crack Growth ◽  
Void Nucleation ◽  
Void Formation ◽  
Aluminum Matrix ◽  
Atomic Scale ◽  
Dynamics Simulation ◽  
Matrix Interface ◽  
Thermally Activated ◽  
Stage Process ◽  
Micrometer Scale

The initial stages of debonding at hard-particle interfaces during rupture is relevant to the fracture of most structural alloys, yet details of the mechanistic process for rupture at the atomic scale are poorly understood. In this study, we employ molecular dynamics simulation of a spherical Al2Cu θ precipitate in an aluminum matrix to examine the earliest stages of void formation and nanocrack growth at the particle-matrix interface, at temperatures ranging from 200–400 K and stresses ranging from 5.7–7.2 GPa. The simulations revealed a three-stage process involving (1) stochastic instantaneous or delayed nucleation of excess free volume at the particle-matrix interface involving only tens of atoms, followed by (2) steady time-dependent crack growth in the absence of dislocation activity, followed by (3) dramatically accelerated crack growth facilitated by crack-tip dislocation emission. While not all three stages were present for all stresses and temperatures, the second stage, termed lattice-trapped delamination, was consistently the rate-limiting process. This lattice-trapped delamination process was determined to be a thermally activated brittle fracture mode with an unambiguous Arrhenius activation energy of 1.37 eV and an activation area of 1.17 Å2. The role of lattice-trapped delamination in the early stages of particle delamination is not only relevant at the high strain-rates and stresses associated with shock spallation, but Arrhenius extrapolation suggests that the mechanism also operates during quasi-static rupture at micrometer-scale particles.

The formation and growth of vacancy loops in magnesium

1968 ◽  
Vol 307 (1488) ◽  
pp. 71-81 ◽  
Keyword(s):  
Surface Oxidation ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Dislocation Loops ◽  
Temperature Range ◽  
Vacancy Loops ◽  
A Value ◽  
Thin Foils ◽  
Contrast Analysis ◽  
Kinetics Of

Single, double and multi-layered dislocation loops have been observed in thin foils of quenched magnesium, and the structure of the loops established by contrast analysis. On annealing in the temperature range 150 to 200°C the loops are observed to grow as a result of the production of vacancies by surface oxidation of magnesium. The kinetics of loop growth have been analysed and a value of 125 ± 25 erg/cm 2 for the stacking fault energy obtained.The reliability and significance of the value in governing the properties of magnesium is discussed.

Contrast From Point Defects in The Infinitesimal Approximation

1980 ◽  
Vol 38 ◽  
pp. 350-351
Author(s):  
L. J. Sykes ◽  
J. J. Hren
Keyword(s):  
Electron Microscope ◽  
Point Defects ◽  
Broad Class ◽  
Stacking Fault ◽  
Crystalline Solids ◽  
Dislocation Loops ◽  
Analytical Expression ◽  
Stacking Fault Tetrahedra

In electron microscope studies of crystalline solids there is a broad class of very small objects which are imaged primarily by strain contrast. Typical examples include: dislocation loops, precipitates, stacking fault tetrahedra and voids. Such objects are very difficult to identify and measure because of the sensitivity of their image to a host of variables and a similarity in their images. A number of attempts have been made to publish contrast rules to help the microscopist sort out certain subclasses of such defects. For example, Ashby and Brown (1963) described semi-quantitative rules to understand small precipitates. Eyre et al. (1979) published a catalog of images for BCC dislocation loops. Katerbau (1976) described an analytical expression to help understand contrast from small defects. There are other publications as well.

scholarly journals On the Proton-Bound Noble Gas Dimers (Ng-H-Ng)+ and (Ng-H-Ng')+ (Ng, Ng'= He-Xe): Relationships betweenStructure, Stability, and Bonding Character

Molecules ◽  
2021 ◽  
Vol 26 (5) ◽  
pp. 1305
Author(s):  
Stefano Borocci ◽  
Felice Grandinetti ◽  
Nico Sanna
Keyword(s):  
Theoretical Calculations ◽  
Noble Gas ◽  
Structure Stability ◽  
Covalent Bonds ◽  
Dissociation Energies ◽  
Non Covalent Interactions ◽  
The Difference ◽  
Noble Gas Dimers ◽  
Covalent Interactions ◽  
Cluster Level

The structure, stability, and bonding character of fifteen (Ng-H-Ng)+ and (Ng-H-Ng')+ (Ng, Ng' = He-Xe) compounds were explored by theoretical calculations performed at the coupled cluster level of theory. The nature of the stabilizing interactions was, in particular, assayed using a method recently proposed by the authors to classify the chemical bonds involving the noble-gas atoms. The bond distances and dissociation energies of the investigated ions fall in rather large intervals, and follow regular periodic trends, clearly referable to the difference between the proton affinity (PA) of the various Ng and Ng'. These variations are nicely correlated with the bonding situation of the (Ng-H-Ng)+ and (Ng-H-Ng')+. The Ng-H and Ng'-H contacts range, in fact, between strong covalent bonds to weak, non-covalent interactions, and their regular variability clearly illustrates the peculiar capability of the noble gases to undergo interactions covering the entire spectrum of the chemical bond.

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