scholarly journals Atomic-Scale Modeling of the Deformation of Nanocrystalline Metals

1998 ◽  
Vol 538 ◽  
Author(s):  
J. Schiotz ◽  
T. Vegge ◽  
K. W. Jacobsen
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Atomic Scale ◽  
Nanocrystalline Metals ◽  
Nanocrystalline Copper ◽  
Impurity Atoms ◽  
Grain Sizes ◽  
Scale Modeling ◽  
Dynamics Simulations ◽  
Computational Resources

AbstractNanocrystalline metals, i.e. metals with grain sizes from 5 to 50 nm, display technologically interesting properties, such as dramatically increased hardness, increasing with decreasing grain size. Due to the small grain size, direct atomic-scale simulations of plastic deformation of these materials are possible, as such a polycrystalline system can be modeled with the computational resources available today.We present molecular dynamics simulations of nanocrystalline copper with grain sizes up to 13 nm. Two different deformation mechanisms are active, one is deformation through the motion of dislocations, the other is sliding in the grain boundaries. At the grain sizes studied here the latter dominates, leading to a softening as the grain size is reduced. This implies that there is an “optimal” grain size, where the hardness is maximal.Since the grain boundaries participate actively in the deformation, it is interesting to study the effects of introducing impurity atoms in the grain boundaries. We study how silver atoms in the grain boundaries influence the mechanical properties of nanocrystalline copper.

scholarly journals Effect of Grain Size on Carburization Characteristics of the High-Entropy Equiatomic CoCrFeMnNi Alloy

Materials ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7199
Author(s):  
Hyunbin Nam ◽  
Jeongwon Kim ◽  
Namkyu Kim ◽  
Sangwoo Song ◽  
Youngsang Na ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Grain Sizes ◽  
Fine Grain ◽  
Cast Specimen ◽  
Vacuum Carburization ◽  
Cold Rolled ◽  
Face Centered

In this study, the carburization characteristics of cast and cold-rolled CoCrFeMnNi high-entropy alloys (HEAs) with various grain sizes were investigated. All specimens were prepared by vacuum carburization at 940 °C for 8 h. The carburized/diffused layer was mainly composed of face-centered cubic structures and Cr7C3 carbide precipitates. The carburized/diffused layer of the cold-rolled specimen with a fine grain size (~1 μm) was thicker (~400 μm) than that of the carburized cast specimen (~200 μm) with a coarse grain size (~1.1 mm). In all specimens, the carbides were formed primarily through grain boundaries, and their distribution varied with the grain sizes of the specimens. However, the carbide precipitates of the cast specimen were formed primarily at the grain boundaries and were unequally distributed in the specific grains. Owing to the non-uniform formation of carbides in the carburized cast specimen, the areas in the diffused layer exhibited various carbide densities and hardness distributions. Therefore, to improve the carburization efficiency of equiatomic CoCrFeMnNi HEAs, it is necessary to refine the grain sizes.

Simulation of the interaction of plastic zone dislocations with the grain boundary at brittle-plastic transition temperatures in molybdenum

2021 ◽  
Vol 2021 (3) ◽  
pp. 77-85
Author(s):  
K. M. Borysovska ◽  
◽  
N. M. Marchenko ◽  
Yu. M. Podrezov ◽  
S. O. Firstov ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Grain Boundary ◽  
Plastic Zone ◽  
Grain Boundaries ◽  
Crack Tip ◽  
Dynamics Simulation ◽  
Density Of Dislocations ◽  
Grain Sizes ◽  
Pile Up

The (DD) method was used to model the formation of the plastic zone of the top of the cracks in polycrystalline molybdenum. Special attention was paid to take into account the interaction of dislocations in the plastic zone with grain boundaries. Structural sensitivity of fracture toughness was analyzed under brittle-ductile condition. Simulations were performed for a range of grain sizes from 400 to 100 μm, at which a sudden increase in fracture toughness with a decrease of grain size was experimentally shown. We calculated the value of K1c taking into account the shielding action of dislocations. The position of all dislocations in the plastic zone at fracture moment was calculated. Based on these data, we obtained the dependences of dislocation density on the distance from the crack tip thereby confirming significant influence of the grain boundaries on plastic zone formation. At large grain sizes, when the plastic zone does not touch the boundary, the distribution of dislocations remained unchanged. As grains reduce their size to size of the plastic zone, they start formating a dislocation pile – up near the boundaries. Dislocations on plastic zone move slightly toward the crack tip, but the density of dislocations in the middle of the grain remains unchanged, and fracture toughness remains almost unchanged. Further reduction of the grain size leads to the Frank-Reed source activation on the grain boundary Forming dislocation pile-up of the neighbor grains. Its stress concentration acts on dislocations of the first grain and causes redistribution of plastic zone dislocations. If the reduction in grain size is not enough to form a strong pile-up, density of dislocations on plastic zone increases slightly and crack resistance increases a few percent. Further reduction of grains promotes strong pile-up, dislocations move to crack tip, and its density on plastic zone increases. Crack is shielded and fracture toughness increases sharply. The calculation showed that the fracture toughness jump is observed at grain sizes of 100—150 μm, in good agreement with the experiment. Keywords: dislocation dynamics simulation, molybdenum, fracture toughness, grain size, plastic zone, brittle-ductile transition.

Atomistic models of triple junctions and the origin of topological changes in microstructural evolution

2000 ◽  
Vol 652 ◽  
Author(s):  
Alessandra Satta ◽  
Luciano Colombo ◽  
Fabrizio Cleri
Keyword(s):  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Level Structure ◽  
Atomic Scale ◽  
Triple Junctions ◽  
Line Energy ◽  
Mesoscopic Models ◽  
Scale Modelling ◽  
Dynamics Simulations ◽  
Topological Changes

ABSTRACTTriple junctions are crucial elements in microstructural evolution: for example, their mobility can be rate-limiting if lower than that of grain boundaries. However, very little is known about their atomic-level structure and properties. We studied the atomic structure of multiple-twin triple junctions in silicon, formed by the convergence of two {111} and one {221} symmetric-tilt grain boundaries. Molecular dynamics simulations with the Stillinger-Weber potential and constant-traction border conditions were performed on several triple junction configurations, obtained by different combinations of the three grain boundaries. All the configurations have a positive excess line energy, a measurable volume contraction and display regions of opposite, tensile and compressive, residual stress. Moreover, we tried to elucidate the role of triple junctions as being the seeds of the only microscopic events that can lead to topological changes in the microstructure. Such events, usually dubbed T1 and T2 in mesoscopic models, correspond to grain switching (in the Ashby-Verrall sense) and grain-disappearance events, respectively. We present preliminary results for the atomic-scale modelling of both classes of topological events and discuss the connection between atomistic and mesoscopic modelling of microstructural evolution.

More Efficient Capture of Bacteria on Nanostructured Materials

2004 ◽  
Vol 845 ◽  
Author(s):  
Thomas J. Webster ◽  
Jin X. Liu ◽  
Margaret K. Banks
Keyword(s):  
Grain Size ◽  
Pseudomonas Fluorescens ◽  
Mammalian Cells ◽  
Positive Response ◽  
Atomic Scale ◽  
One Dimension ◽  
Biological Applications ◽  
Environmental Filters ◽  
Grain Sizes ◽  
Nanophase Materials

ABSTRACTNanobiotechnology is a growing area of research, primarily due to the potentially numerous applications of new synthetic nanomaterials in engineering/science. Although various definitions have been given to the word “nanomaterials” by many different experts, the commonly accepted one refers nanomaterials as those materials which possess grains, particles, fibers, or other constituent components that have one dimension specifically less than 100 nm. In biological applications, most of the research to date has focused on the interactions between mammalian cells and synthetic nanophase surfaces for the creation of better tissue engineering materials. Although mammalian cells have shown a definite positive response to nanophase materials, the evidence for bacteria interactions with nanophase materials remains for the most part a mystery. For this reason, this study determined the capture of a model bacteria (Pseudomonas fluorescens) on nanophase compared to conventional grain size alumina. Results provided the first evidence of increased capture of Pseudomonas fluorescens on alumina with nanometer compared to conventional grain sizes. Although not measured at the atomic scale, similar chemistry, crystallinity, crystal phase, and porosity was observed between nanophase and conventional alumina. For this reason, a major material property difference between nanophase and conventional alumina was reduced grain size (and perhaps associated changes in charge density) which led to increased bacteria capture and the design of better environmental filters.

Dislocations in Submicron Grain Size and Nanocrystalline Copper

2000 ◽  
Vol 634 ◽  
Author(s):  
T. Ungár ◽  
G. Tichy ◽  
P. G. Sanders ◽  
J. R. Weertman
Keyword(s):  
Grain Size ◽  
Profile Analysis ◽  
Dislocation Model ◽  
X Ray Diffraction ◽  
Strain Anisotropy ◽  
Nanocrystalline Copper ◽  
X Ray ◽  
Gas Condensation ◽  
Grain Sizes ◽  
20 Nm

ABSTRACTUsing the dislocation model of strain anisotropy in X-ray diffraction peak profile analysis it is shown that in nanocrystalline copper produced by inert gas condensation dislocations are present, at least, down to average grain sizes of the order of 20 nm. Based on the analysis of the dislocation contrast factors it is suggested that with decreasing grain size the proportion of Lomer-Cottrell type dislocations increases.

Molecular Dynamics Simulations of Damage Cascades Creation in Oxide-Particle-Embedded Fe

2017 ◽  
Author(s):  
A. M. Mustafa ◽  
Zhongyu Li ◽  
Lin Shao
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Oxide Particle ◽  
Oxide Dispersion Strengthened ◽  
Atomic Scale ◽  
Scale Modeling ◽  
Alloy Type ◽  
Oxide Particles ◽  
Ods Alloys ◽  
Dynamics Simulations

Oxide-dispersion-strengthened (ODS)alloys have been identified as one promising candidate alloy type for high temperature reactor applications. Understanding irradiation stability of ODS alloys relies on atomic scale modeling such as molecular dynamics simulations. In this study, yttrium and oxygen charges in Y2O3 oxide particles, which are embedded in pure Fe matrix, are optimized to achieve stabilities observed in experiments. Deviation from the optimized charges causes self-explosion and instability of oxide particles. Molecular dynamics simulations further show that under such optimized charge conditions, damage cascade creation and defect developments can be appropriately modeled.

Atomic-Scale Modeling of Low-Energy Ion-Solid Processes

1988 ◽  
Vol 129 ◽  
Author(s):  
Brian W. Dodson
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Low Energy ◽  
Atomic Scale ◽  
Scale Modeling ◽  
Dynamics Simulations

ABSTRACTVarious techniques which have been applied to modeling low-energy (≪ 1 keV) ion-solid interactions on an atomistic scale are described. In addition to their individual strengths, all such methods also have a number of drawbacks, both fundamental and practical. The range of validity, and the problems encountered external to this range, will be outlined for the different approaches. Finally, examples of molecular dynamics simulations of low-energy ion-solid interactions will be presented.

Atomic-Scale Modeling of Low-Energy Ion-Solid Processes

1988 ◽  
Vol 128 ◽  
Author(s):  
Brian W. Dodson
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Low Energy ◽  
Atomic Scale ◽  
Scale Modeling ◽  
Dynamics Simulations

ABSTRACTVarious techniques which have been applied to modeling low-energy (<< 1 keV) ion-solid interactions on an atomistic scale are described. In addition to their individual strengths, all such methods also have a number of drawbacks, both fundamental and practical. The range of validity, and the problems encountered external to this range, will be outlined for the different approaches. Finally, examples of molecular dynamics simulations of low-energy ion-solid interactions will be presented.

Grain-size dependence of mechanical properties in polycrystalline boron-nitride: a computational study

2015 ◽  
Vol 17 (34) ◽  
pp. 21894-21901 ◽  
Author(s):  
Matthew Becton ◽  
Xianqiao Wang
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Grain Size ◽  
Boron Nitride ◽  
Molecular Dynamics Simulations ◽  
Failure Mechanism ◽  
Size Dependence ◽  
Computational Study ◽  
Grain Sizes ◽  
Dynamics Simulations

Molecular dynamics simulations are performed to investigate the mechanical properties and failure mechanism of polycrystalline boron nitride sheet with various grain sizes.

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