scholarly journals Effect of light elements impurity atoms on grain boundary diffusion in FCC metals: a molecular dynamics simulation

2020 ◽  
Vol 62 (12) ◽  
pp. 930-935
Author(s):  
G. M. Poletaev ◽  
I. V. Zorya ◽  
R. Yu. Rakitin ◽  
M. D. Starostenkov
Keyword(s):  
Molecular Dynamics ◽  
Grain Boundary ◽  
Crystal Lattice ◽  
Grain Boundaries ◽  
Free Volume ◽  
Misorientation Angle ◽  
Light Elements ◽  
Self Diffusion ◽  
Impurity Atoms ◽  
Metal Atoms

Effect of carbon and oxygen impurity atoms on diffusion along the tilt grain boundaries with <100> and <111> misorientation axis in metals with FCC lattice was studied by mean of molecular dynamics method. Ni, Ag, and Al were considered as metals. Interactions of metal atoms with each other were described by many-particle Clery-Rosato potentials constructed within the framework of tight binding model. To describe interactions of atoms of light elements impurities with metal atoms and atoms of impurities with each other, Morse pair potentials were used. According to obtained results, impurities in most cases lead to an increase in self-diffusion coefficient along the grain boundaries, which is caused by deformation of crystal lattice near the impurity atoms. Therefore, additional distortions and free volume are formed along the boundaries. It is more expressed for carbon impurities. Moreover, with an increase in concentration of carbon in the metal, an increase in coefficient of grain-boundary self-diffusion was observed first, and then a decrease followed. This behavior is explained by formation of aggregates of carbon atoms at grain boundary, which leads to partial blocking of the boundary. Oxygen atoms had smaller effect on diffusion along the grain boundaries, which is apparently explained by absence of a tendency to form aggregates and lesser deformation of crystal lattice around impurity. The greatest effect of impurities on self-diffusion along the grain boundaries among the examined metals was observed for nickel. Nickel has the smallest lattice parameter, impurity atoms deform its lattice around itself more than aluminum and silver, and therefore they create relatively more lattice distortions in it and additional free volume along the grain boundaries, which lead to an increase in diffusion permeability. Diffusion coefficients along the high-angle boundaries with misorientation angle of 30° turned out to be approximately two times higher than along low-angle boundaries with a misorientation angle of 7°. Diffusion along the <100> grain boundaries flowed more intensively than along the <111> boundaries.

scholarly journals Effect of light elements impurity on process of nickel crystallization near the triple interface of grain boundaries: a molecular dynamics simulation

2020 ◽  
Vol 63 (5) ◽  
pp. 357-363
Author(s):  
I. V. Zorya ◽  
G. M. Poletaev ◽  
M. D. Starostenkov ◽  
R. Yu. Rakitin ◽  
D. V. Kokhanenko
Keyword(s):  
Molecular Dynamics ◽  
Boundary Conditions ◽  
Crystal Lattice ◽  
Grain Boundaries ◽  
Melting Temperature ◽  
Crystallization Front ◽  
Light Elements ◽  
Cylinder Axis ◽  
Impurity Atoms ◽  
Effect Of Impurities

Molecular dynamics method was used to study the effect of impurities of light elements of carbon, nitrogen and oxygen on crystallization process near the triple interface of grain boundaries in nickel. Tilt boundaries with misorientation axis <111> were considered as the grain boundaries. Interactions of nickel atoms with each other were described by many-particle Clery-Rosato potential constructed within the framework of the tight binding model. To describe interactions of atoms of light elements impurities with nickel atoms and atoms of impurities with each other, Morse pair potentials were used. Calculation cell had a shape of cylinder, axis of which coincided with the line of triple interface and the axis of grain misorientation. Periodic boundary conditions were imposed along the cylinder axis, and the atoms on side surface of cylinder were motionless. To simulate crystallization, calculation cell was melted by heating to a temperature well above the melting temperature of nickel. After the simulated polycrystal become liquid, the thermostat was turned on and held at a constant temperature below the melting temperature. Rigid boundary conditions on the lateral surface of cylindrical calculation cell in this case simulated crystallization fronts from three crystallization centers. The area near the triple interface had crystallized the last. In this area, defects and free volume were concentrated. Presence of impurities led to a significant slowdown in the rate of crystallization. With introduction of 10 % of impurity atoms, the rate of motion of crystallization front decreased several times. The effect of impurities on crystallization rate was enhanced in C – N – O direction, which is due to difference in crystal lattice deformation caused by impurity atoms. The greater this deformation was, the stronger was impurity atoms inhibit crystallization front. Formation of aggregates at fairly high concentrations was typical for impurity carbon atoms. Crystallization front had impeded on these aggregates. The oxygen and nitrogen atoms did not form aggregates. However, due to distortions of crystal lattice caused by them, they also strongly slowed down the crystallization front.

Structural and Mechanical Properties of Nanophase Ni: A Molecular-Dynamics Study of the Influence of Grain-Boundary Structure on Elastic and Plastic Behavior

1997 ◽  
Vol 492 ◽  
Author(s):  
H. Van Swygenhoven ◽  
M. Spaczér ◽  
A. Caro
Keyword(s):  
Molecular Dynamics ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Diffusion Mechanism ◽  
Distribution Functions ◽  
Boundary Structure ◽  
Plastic Behavior ◽  
Self Diffusion ◽  
Common Neighbour ◽  
Grain Boundary Structure

ABSTRACTMolecular dynamics computer simulations of high load plastic deformation at temperatures up to 500K of Ni nanophase samples with mean grain size of 5 nm are reported. Two types of samples are considered: a polycrystal nucleated from different seeds, each having random location and random orientation, representing a sample with mainly high angle grain boundaries, and polycrystals with seeds located at the same places as before, but with a limited missorientation representing samples with mainly low angle grain boundaries. The structure of the grain boundaries is studied by means of pair distribution functions, coordination number, atom energetics, and common neighbour analysis. Plastic behaviour is interpreted in terms of grain-boundary viscosity, controlled by a self diffusion mechanism at the disordered interface activated by thermal energy and stress.

scholarly journals Recrystallization from a Three-Grain Crystalline Iron

2015 ◽  
Vol 2015 ◽  
pp. 1-6
Author(s):  
Bo Zhao ◽  
Shanshan Chen ◽  
Jinfan Huang ◽  
Lawrence S. Bartell
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Solid State ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Misorientation Angle ◽  
Dynamics Simulation ◽  
Iron Nanoparticle ◽  
Critical Nuclei ◽  
Solid State Recrystallization

The solid state recrystallization and grain boundary migrations in an iron nanoparticle Fe2616 with three grains were studied by a molecular dynamics simulation. It was found that nucleation rates could be determined as the smaller grains were consumed by the larger ones. Moreover, the grain disorder was more important than the misorientation angle in governing the rates. Suggestions about the critical nuclei for the recrystallization are proposed. No obvious interaction between the grain boundaries was observed in the example studied in this report.

Molecular Dynamics Analysis of the Acceleration of Intergranular Cracking of Ni-Base Superalloy Caused by Accumulation of Vacancies and Dislocations Around Grain Boundaries

2020 ◽  
Author(s):  
Ryo Kikuchi ◽  
Shujiro Suzuki ◽  
Ken Suzuki
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Fatigue Loading ◽  
Transgranular Fracture ◽  
Dynamics Analysis ◽  
Intergranular Cracking ◽  
Creep Fatigue ◽  
Schmid Factor

Abstract Ni-based superalloys with excellent high temperature strength have been used in advanced thermal power plants. It was found that grain boundary cracking is caused in the alloy under creep-fatigue loading due to the degradation of the crystallinity of grain boundaries and the grain boundary cracking degrades the lifetime of the alloy drastically. In order to clarify the mechanism of intergranular cracking, in this research, static and dynamic strains were applied to a bicrystal structure of the alloy perpendicularly to the grain boundary using molecular dynamics analysis. In addition, the effect of the accumulation of vacancies in the area with high-density of dislocations on the strength of the bicrystal structure was analysed. It was found that the fracture mode of the bicrystal structure changed from ductile transgranular fracture to brittle intergranular one as strong functions of the combination of Schmid factor of the two grains and the density of defects around the grain boundary. The local heavy plastic deformation occurred around the grain boundary with large difference in Schmid factor between nearby grains and the diffusion of the newly grown dislocations and vacancies was suppressed by the large strain field due to the large mismatch of the crystallographic orientation between the grains. The accumulation of vacancies accelerated the local plastic deformation around the grain boundary. Therefore, the mechanism of the acceleration of intergranular cracking under creep-fatigue loading was successfully clarified by MD analysis.

scholarly journals Molecular Dynamics Study on the Impact of Cu Clusters at the BCC-Fe Grain Boundary on the Tensile Properties of Crystal

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1533
Author(s):  
Haichao Zhang ◽  
Xufeng Wang ◽  
Huirong Li ◽  
Changqing Li ◽  
Yungang Li
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Tensile Properties ◽  
Structural Phase ◽  
Structural Phase Transformation ◽  
Tensile Process ◽  
Deformation Ability ◽  
The Impact

The molecular dynamics (MD) method was used to simulate and calculate the segregation energy and cohesive energy of Cu atoms at the Σ3{111}(110) and Σ3{112}(110) grain boundaries, and the tensile properties of the BCC-Fe crystal, with the grain boundaries containing coherent Cu clusters of different sizes (a diameter of 10 Å, 15 Å and 20 Å). The results showed that Cu atoms will spontaneously segregate towards the grain boundaries and tend to exist in the form of large-sized, low-density Cu clusters at the grain boundaries. When Cu cluster exists at the Σ3{111}(110) grain boundary, the increase in the size of the Cu cluster leads to an increase in the probability of vacancy formation inside the Cu cluster during the tensile process, weakening the breaking strength of the crystal. When the Cu cluster exists at the Σ3{112}(110) grain boundary, the Cu cluster with a diameter of 10 Å will reduce the strain hardening strength of the crystal, but the plastic deformation ability of the crystal will not be affected, and the existence of Cu clusters with a diameter of 15 Å and 20 Å will suppress the structural phase transformation of the crystal, and significantly decrease the plastic deformation ability of the crystal, thereby resulting in embrittlement of the crystal.

scholarly journals A molecular dynamics study on the tribological behavior of molybdenum disulfide with grain boundary defects during scratching processes

Friction ◽  
2020 ◽  
Author(s):  
Boyu Wei ◽  
Ning Kong ◽  
Jie Zhang ◽  
Hongbo Li ◽  
Zhenjun Hong ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Wear Resistance ◽  
Grain Boundary ◽  
Molybdenum Disulfide ◽  
Adhesion Strength ◽  
Misorientation Angle ◽  
Tribological Behavior ◽  
Md Simulations ◽  
Breaking Load ◽  
Indentation Process

AbstractThe effect of grain boundary (GB) defects on the tribological properties of MoS2 has been investigated by molecular dynamics (MD) simulations. The GB defects-containing MoS2 during scratching process shows a lower critical breaking load than that of indentation process, owing to the combined effect of pushing and interlocking actions between the tip and MoS2 atoms. The wear resistance of MoS2 with GB defects is relevant to the misorientation angle due to the accumulation of long Mo-S bonds around the GBs. Weakening the adhesion strength between the MoS2 and substrate is an efficient way to improve the wear resistance of MoS2 with low-angle GBs.

scholarly journals The Effects of Grain Boundary Misorientation on the Mechanical Properties and Mechanism of Plastic Deformation of Ni/Ni3Al: A Molecular Dynamics Study

Materials ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 5715
Author(s):  
Jun Ding ◽  
Sheng-Lai Zhang ◽  
Quan Tong ◽  
Lu-Sheng Wang ◽  
Xia Huang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Grain Boundary ◽  
Misorientation Angle ◽  
Interfacial Energy ◽  
Stacking Faults ◽  
Boundary Misorientation ◽  
Grain Boundary Misorientation ◽  
Mechanisms Of Plastic Deformation

The effects of grain boundary misorientation angle (θ) on mechanical properties and the mechanism of plastic deformation of the Ni/Ni3Al interface under tensile loading were investigated using molecular dynamics simulations. The results show that the space lattice arrangement at the interface is dependent on grain boundary misorientations, while the interfacial energy is dependent on the arrangement. The interfacial energy varies in a W pattern as the grain boundary misorientation increases from 0° to 90°. Specifically, the interfacial energy first decreases and then increases in both segments of 0–60° and 60–90°. The yield strength, elastic modulus, and mean flow stress decrease as the interfacial energy increases. The mechanism of plastic deformation varies as the grain boundary misorientation angle (θ) increases from 0° to 90°. When θ = 0°, the microscopic plastic deformation mechanisms of the Ni and Ni3Al layers are both dominated by stacking faults induced by Shockley dislocations. When θ = 30°, 60°, and 80°, the mechanisms of plastic deformation of the Ni and Ni3Al layers are the decomposition of stacking faults into twin grain boundaries caused by extended dislocations and the proliferation of stacking faults, respectively. When θ = 90°, the mechanisms of plastic deformation of both the Ni and Ni3Al layers are dominated by twinning area growth resulting from extended dislocations.

Effects of Alloying Elements on Iron Grain Boundary Cohesion

1997 ◽  
Vol 492 ◽  
Author(s):  
X. Chen ◽  
D. E. Ellis ◽  
G. B. Olson
Keyword(s):  
Molecular Dynamics ◽  
Free Surface ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
First Principles ◽  
Electronic Structure Calculations ◽  
Alloying Elements ◽  
Alloying Element ◽  
Long Time ◽  
Structure Calculations

For a long time, understanding the mechanisms of impurity-promoted embrittlement in iron and the consequent cohesion(decohesion) effects has been a challenge for materials scientists. The role alloying elements play in impurity-promoted embrittlement is important due to either their direct intergranular cohesion(decohesion) effects or effects upon embrittling potency of other impurities. Some alloying elements like Pd and Mo are known to be helpful for intergranular cohesion in iron and some other alloying elements like Mn are known to segregate to and weaken iron grain boundaries dramatically[1]. There have been intensive investigations on these mechanisms for a long time and especially, with the progress in computing techniques in recent years, calculations on more realistic models have become possible[2–4]. In this paper we briefly present our studies on some selected alloying-element/iron grain boundaries(GB) and free surface(FS) systems. The effects of Pd, Mo, Mn and Cr on the Fe Σ5 (031) grain boundary and its corresponding (031) free surface are examined, using a combination of molecular dynamics(MD) and first-principles electronic structure calculations. Section 2 gives a brief introduction to the methods used and Section 3 gives the main results.

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