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.

Atomic Scale Modelling of the Primary Damage State of Irradiated UO2 Matrix

2006 ◽  
Vol 981 ◽  
Author(s):  
Laurent Van Brutzel ◽  
Jean-Paul Crocombette
Keyword(s):  
Grain Boundary ◽  
Point Defects ◽  
Large Scale ◽  
Recoil Nucleus ◽  
Atomic Scale ◽  
Damage State ◽  
Stable Clusters ◽  
Scale Modelling ◽  
Primary Damage ◽  
Dynamics Simulations

AbstractLarge scale classical molecular dynamics simulations have been carried out to study the primary damage state due to a-decay self irradiation in UO2 matrix. Simulations of energetic displacement cascades up to the realistic energy of the recoil nucleus at 80 keV provide new informations on defect production, their spatial distribution and their clustering. The discrepancy with the classical linear theory NRT (Norton-Robinson-Torrens) law on the creation of the number of point defects is discussed. Study of cascade overlap sequence shows a saturation of the number of point defects created as the dose increases. Toward the end of the overlap sequence, large stable clusters of vacancies are observed. The values of athermal diffusion coefficients coming from the ballistic collisions and the additional point defects created during the cascades are estimated from these simulations to be, in all the cases, less than 10-26 m2/s. Finally, the influence of a grain boundary of type Sigma5 is analysed. It has been found that the energy of the cascades are dissipated along the interface and that most of the point defects are created at the grain boundary.

scholarly journals Coupled atomistic-mesoscopic model of polycrystalline plasticity

2001 ◽  
Vol 677 ◽  
Author(s):  
Fabrizio Cleri ◽  
Gregorio D'Agostino ◽  
Alessandra Satta ◽  
Luciano Colombo
Keyword(s):  
Grain Boundaries ◽  
Mesoscale Model ◽  
Triple Junctions ◽  
Extended Defect ◽  
Statistical Population ◽  
Mesoscopic Model ◽  
Level Information ◽  
Defect Interactions ◽  
Dynamics Simulations ◽  
Distribution Of Dislocations

ABSTRACTWe discuss a microstructure evolution framework which couples atomic-level information about extended-defect interactions into a mesoscopic model; the latter, in turn, describes the dy-namic evolution of a statistical population of grain boundaries and dislocations. Atomistic simulations are carried out by means of molecular dynamics simulations on both isolated and interacting dislocations, grain boundaries, triple junctions, microcracks; the reference material for such studies is, at present, Silicon with the Stillinger-Weber potential. The mesoscale model describes the motion of discrete triple junctions (and, consequently, of the continuous network of adjoining grain boundaries) embedded in a continuous medium containing a homogenous, evolving distribution of dislocations.

Molecular Dynamics Simulations of Nanocrystalline Nickel and Copper Revealing Different Failure Model of FCC Metals

2009 ◽  
Vol 633-634 ◽  
pp. 31-38
Author(s):  
Ajing Cao
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Grain Boundaries ◽  
Large Scale ◽  
Uniaxial Tensile ◽  
Face Centered Cubic ◽  
Triple Junctions ◽  
Fcc Metals ◽  
Face Centered ◽  
Dynamics Simulations

We have previously reported that the fracture behavior of nanocrystalline (NC) Ni is via the nucleation and coalescence of nano-voids at grain boundaries and triple junctions, resulting in intergranular failure mode. Here we show in large-scale molecular dynamics simulations that partial-dislocation-mediated plasticity is dominant in NC Cu with grain size as small as ~ 10 nanometers. The simulated results show that NC Cu can accommodate large plastic strains without cracking or creating damage in the grain interior or grain boundaries, revealing their intrinsic ductile properties compared with NC Ni. These results point out different failure mechanisms of the two face-centered-cubic (FCC) metals subject to uniaxial tensile loading. The insight gained in the computational experiments could explain the good plasticity found in NC Cu not seen in Ni so far.

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.

Plastic deformation of nanocrystalline copper-antimony alloys

2010 ◽  
Vol 25 (3) ◽  
pp. 411-421 ◽  
Author(s):  
Rahul K. Rajgarhia ◽  
Douglas E. Spearot ◽  
Ashok Saxena
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Grain Boundaries ◽  
Partial Dislocation ◽  
Dislocation Nucleation ◽  
Uniaxial Tensile ◽  
Triple Junctions ◽  
Dopant Atoms ◽  
Dynamics Simulations ◽  
Antimony Alloys

Molecular dynamics simulations are used to evaluate the influence of Sb dopant atoms at the grain boundaries on plastic deformation of nanocrystalline Cu. Deformation is conducted under uniaxial tensile loading, and Sb atoms are incorporated as substitutional defects at the grain boundaries. The presence of randomly dispersed Sb atoms at the grain boundaries does not appreciably influence the mechanisms associated with dislocation nucleation in nanocrystalline Cu; grain boundary ledges and triple junctions still dominate as partial dislocation sources. However, the magnitude of the tensile stress associated with the partial dislocation nucleation event does increase with increasing Sb concentration and also with increasing grain size. The flow stress of nanocrystalline Cu increases with increasing Sb concentration up to 1.0 at.% Sb, with a maximum observed at a grain size of 15 nm for all Sb concentrations (0.0–2.0 at.% Sb).

Effect of Grain Boundaries on Fracture Toughness in Ultrafine-Grained Metals by Atomic-Scale Computational Experiments

2012 ◽  
Vol 706-709 ◽  
pp. 1841-1846
Author(s):  
Tomotsugu Shimokawa ◽  
Masaki Tanaka ◽  
Kenji Higashida
Keyword(s):  
Fracture Toughness ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Atomic Scale ◽  
Boundary Structure ◽  
Shielding Effect ◽  
Mechanical Field ◽  
Ultrafine Grained ◽  
Crack Tips ◽  
Dynamics Simulations

In order to investigate roles of grain boundaries on the improved fracture tough-ness in ultrafine-grained metals, interactions between crack tips, dislocations, and disclinationdipoles at grain boundaries are performed to aluminium bicrystal models containing a crackand h112i tilt grain boundaries using molecular dynamics simulations. A proposed mechanismto express the improved fracture toughness in ultrafine-grained metals is the disclination shield-ing effect on the crack tip mechanical field. The disclination shielding can be activated whena transition of dislocation sources from crack tips to grain boundaries and a transition of thegrain boundary structure into a neighbouring energetically stable boundary by emitting dis-locations from the grain boundary occur. The disclination shielding effect becomes large asdislocations are continuously emitted from the grain boundary without dislocation emissionsfrom crack tips. This mechanism can further shield the mechanical field around the crack tipand obtain the plastic deformation by dislocation emissions from grain boundaries, hence itcan be expected that the disclination shielding effect can improve the fracture toughness inultrafine-grained metals

scholarly journals Microstructural evolution during high-temperature tensile creep at 1,500°C of a MoSiBTiC alloy

2020 ◽  
Vol 39 (1) ◽  
pp. 136-145 ◽  
Author(s):  
Sojiro Uemura ◽  
Shiho Yamamoto Kamata ◽  
Kyosuke Yoshimi ◽  
Sadahiro Tsurekawa
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Grain Boundary Sliding ◽  
Primary Creep ◽  
Tensile Creep ◽  
Tertiary Creep ◽  
Continuous Dynamic Recrystallization ◽  
Continuous Dynamic ◽  
Creep Regime

AbstractMicrostructural evolution in the TiC-reinforced Mo–Si–B-based alloy during tensile creep deformation at 1,500°C and 137 MPa was investigated via scanning electron microscope-backscattered electron diffraction (SEM-EBSD) observations. The creep curve of this alloy displayed no clear steady state but was dominated by the tertiary creep regime. The grain size of the Moss phase increased in the primary creep regime. However, the grain size of the Moss phase was found to remarkably decrease to <10 µm with increasing creep strain in the tertiary creep regime. The EBSD observations revealed that the refinement of the Moss phase occurred by continuous dynamic recrystallization including the transformation of low-angle grain boundaries to high-angle grain boundaries. Accordingly, the deformation of this alloy is most likely to be governed by the grain boundary sliding and the rearrangement of Moss grains such as superplasticity in the tertiary creep regime. In addition, the refinement of the Moss grains surrounding large plate-like T2 grains caused the rotation of their surfaces parallel to the loading axis and consequently the cavitation preferentially occurred at the interphases between the end of the rotated T2 grains and the Moss grains.

scholarly journals Local structure and distortions of mixed methane-carbon dioxide hydrates

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Bernadette R. Cladek ◽  
S. Michelle Everett ◽  
Marshall T. McDonnell ◽  
Matthew G. Tucker ◽  
David J. Keffer ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Exchange Process ◽  
Carbon Dioxide Sequestration ◽  
Distribution Functions ◽  
Atomic Scale ◽  
Mixed Gas ◽  
Pure Compounds ◽  
Dynamics Simulations ◽  
Pair Distribution Functions ◽  
Methane Carbon

AbstractA vast source of methane is found in gas hydrate deposits, which form naturally dispersed throughout ocean sediments and arctic permafrost. Methane may be obtained from hydrates by exchange with hydrocarbon byproduct carbon dioxide. It is imperative for the development of safe methane extraction and carbon dioxide sequestration to understand how methane and carbon dioxide co-occupy the same hydrate structure. Pair distribution functions (PDFs) provide atomic-scale structural insight into intermolecular interactions in methane and carbon dioxide hydrates. We present experimental neutron PDFs of methane, carbon dioxide and mixed methane-carbon dioxide hydrates at 10 K analyzed with complementing classical molecular dynamics simulations and Reverse Monte Carlo fitting. Mixed hydrate, which forms during the exchange process, is more locally disordered than methane or carbon dioxide hydrates. The behavior of mixed gas species cannot be interpolated from properties of pure compounds, and PDF measurements provide important understanding of how the guest composition impacts overall order in the hydrate structure.

MICROSTRUCTURAL EVOLUTION OF Al-Cu-Mg-Ag ALLOY WITH TRACE Zr ADDITION DURING TWO-STEP HOMOGENIZATION

2009 ◽  
Vol 23 (06n07) ◽  
pp. 855-862 ◽  
Author(s):  
FEIYUE MA ◽  
ZHIYI LIU
Keyword(s):  
Melting Point ◽  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Cast Alloy ◽  
Scanning Calorimetry ◽  
Zr Addition ◽  
Homogenization Time ◽  
The Matrix ◽  
Higher Temperature ◽  
Lower Temperature

The microstructural evolution in an Al - Cu - Mg - Ag alloy with trace Zr addition during homogenization treatment was characterized by Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray Spectroscopy (EDS). It was shown that the low-melting-point phase segregating toward grain boundaries is Al 2 Cu , with a melting point of 523.52°C. A two-step homogenization process was employed to optimize the microstructure of the as-cast alloy, during which the alloy was first homogenized at a lower temperature, then at a higher temperature. After homogenized at 420°C for 6 h, Al 3 Zr particles were finely formed in the matrix. After that, when the alloy was homogenized at an elevated temperature for a longer time, i.e., 515°C for 24 h, most of the precipates at the grain boundaries were removed. Furthermore, the dispersive Al 3 Zr precipitates were retained, without coarsening greatly in the final homogenization step. A kinetics model is employed to predict the optimal homogenization time at a given temperature theoretically, and it confirms the result in present study, which is 420°C/6h+515°C/24h.

Sign in / Sign up

Export Citation Format

Share Document