Vacancy Diffusion under a Stress and Kinetic of Nanovoid Growth in Cubic Metals

2014 ◽  
Vol 95 ◽  
pp. 72-77
Author(s):  
Andrei Nazarov ◽  
Alexander Mikheev ◽  
Alexander Zaluzhnyi
Keyword(s):  
Elastic Stress ◽  
Diffusion Processes ◽  
Activation Barrier ◽  
Transformation Kinetic ◽  
Elastic Fields ◽  
Cubic Metals ◽  
Bcc Metals ◽  
Nanovoid Growth ◽  
Atom Configuration ◽  
Atom Position

Elastic fields, generating by defects of the structure, influence the diffusion processes. It leads to the alteration of the phase transformation kinetic. One of the chief aims of our work is to obtain general equations for the diffusion fluxes under strain that give the possibility for using these equations at low temperatures, as in this case the strain influence on the diffusion fluxes is manifested in maximal degree. Our approach takes into consideration, that the strains can alter the surrounding atom configuration near the jumping one and consequently the local magnitude of the activation barrier and a rate of atom jump. The rates of atom jumps in different directions define the flux density of the vacancies. Now we take into account, that strain values are different in the saddle point and in the rest atom position, in differ from our consideration that was done by us earlier. As a result in the development of our approach the general equations for the vacancy fluxes are obtained for fcc and bcc metals. In our paper we discuss the main features of the theory of diffusion under stress and its applications. In particular we examine how elastic stress, arising from nanovoids, influence the diffusion vacancy fluxes and the growth rate of voids in metals.

General Approach to Diffusion under a Stress in Metals and Interstitial Alloys

2015 ◽  
Vol 363 ◽  
pp. 112-119 ◽  
Author(s):  
Andrei Nazarov ◽  
Alexander Mikheev
Keyword(s):  
Saddle Point ◽  
Total Energy ◽  
Low Temperatures ◽  
Activation Barrier ◽  
Strain Tensor ◽  
Maximal Degree ◽  
Local Magnitude ◽  
Bcc Metals ◽  
Atom Configuration ◽  
Atom Position

One of the main aims of our work is to obtain general equations for the diffusion fluxes under strain that give the possibility for using these equations at low temperatures, as in this case the strain influence on the diffusion fluxes is manifested in maximal degree. Our approach takes into consideration that the strains can alter the surrounding atom configuration near the jumping atom and consequently the local magnitude of the activation barrier and a rate of atom jumps. The approach is derived under assumptions that the total energy depends on the pair distances only and the attempt frequencies are the same for all jumps. The rates of atom jumps in different directions define the flux density of the defects. Now we take into account that the strain tensor is different at the saddle point and at the rest atom position, that differentiates our approach from previous ones. As a result, general equations for the vacancy fluxes and impurity fluxes are obtained for fcc and bcc metals. These equations differ significantly from those obtained earlier.

Diffusion under a Stress in Metals and Interstitial Alloys

2011 ◽  
Vol 172-174 ◽  
pp. 1156-1163 ◽  
Author(s):  
Andrei V. Nazarov ◽  
Alexander Mikheev ◽  
Irina Valikova ◽  
Alexander Zaluzhnyi
Keyword(s):  
Phase Transformation ◽  
Low Temperatures ◽  
Diffusion Processes ◽  
Transformation Kinetic ◽  
Maximal Degree ◽  
Diffusion In Solids ◽  
Elastic Fields ◽  
Cubic Metals ◽  
Alloy Properties ◽  
Phase Transformation Kinetic

Elastic fields, generating by precipitates, cracks, dislocations and other defects of the structure, influence the diffusion processes. It leads to the alteration of the phase transformation kinetic, segregation formation and changes of the alloy properties. However, understanding the effects of strain on diffusion in solids is now limited. One of the chief aims of our approach is to obtain the general equations for the diffusion fluxes under strain that give the possibility of using these equations at low temperatures, as in this case, the strain influence on the diffusion fluxes is manifested in maximal degree. Recently some important generalization of our approach was done and equations for the vacancy fluxes in cubic metals were obtained. Now we have made the next step in the development of approach: general equations for the fluxes in interstitial alloys are obtained for different kinds of jumps in bcc and fcc structures. We are going to discuss the main features of the theory of diffusion under stress, to compare the equations for the fluxes and to present results of theory applications that are obtained with the help of computer simulations.

Kinetics of Void Growth in Cubic Metals: Theory and Simulation

2015 ◽  
Vol 363 ◽  
pp. 91-98 ◽  
Author(s):  
Alexander Mikheev ◽  
Andrei Nazarov ◽  
Irina Ershova ◽  
Alexander Zaluzhnyi
Keyword(s):  
Growth Rate ◽  
Void Growth ◽  
Elastic Stress ◽  
Functional Dependence ◽  
Kinetic Equations ◽  
Elastic Stresses ◽  
Cubic Metals ◽  
Bcc Metals ◽  
Kinetics Of ◽  
Advanced Model

We examine the effect of elastic stresses induced by growing voids on the diffusion vacancy fluxes using newly derived equations. One of the main goals of our work is to obtain a kinetic equation for the growth rate of voids in cubic metals. The diffusion equation for vacancies, in which the influence of elastic stress near the void on the flux is taken into account, is linearized and solved. Then after mathematical transformations that are similar to Lifshitz - Slyozov theory, kinetic equations for the growth rate of the voids in fcc and bcc metals are obtained. The kinetic equations contain additional terms due to developed strain. This feature distinguishes the present equation from known ones and changes the kinetic of void growth. The functional dependence on strain is determined by coefficients, which characterize the strain influence on diffusion (SID coefficients). These coefficients are very sensitive to the atomic structure in the nearest vicinity of the saddle-point configuration. We have built an advanced model to evaluate them. SID coefficient simulation is the next step of this work. Using the kinetic equations and the SID coefficients, we calculate the void growth rate in cubic metals under different conditions.

Calculation of Atom Configuration and Characteristic of Vacancy in bcc Lattice of α-Fe

2006 ◽  
Vol 249 ◽  
pp. 55-60 ◽  
Author(s):  
Irina Valikova ◽  
Andrei V. Nazarov ◽  
Alexandr A. Mikheev
Keyword(s):  
Fine Structure ◽  
Point Defect ◽  
Atomic Structure ◽  
External Pressure ◽  
Static Method ◽  
Elastic Continuum ◽  
Bcc Metals ◽  
Bcc Lattice ◽  
And Migration ◽  
Atom Configuration

This work is devoted to the simulation of atom configurations in bcc metals near the point defect using the molecular static method. The values of migration and formation volumes are very sensitive to the atomic structure in the vicinity of a defect, which makes it necessary to consider a large number of atoms in the computation cell and to take into account an elastic matrix around the cell. We have developed the new model taking into consideration these factors. It allows defining the “fine structure” of displacement atoms near the point defect. The atoms of third zone were embedded in an elastic continuum. The displacement of each atom embedded in an elastic continuum was defined as the first and the second terms in solution of elastic equation. In the framework of this model we calculated the formation and migration energies and volumes of defect. Also we take into consideration that the energy of system (in particular the system with defect) depends on the external pressure. This dependence gives an addition to the values of migration and formation volumes.

Simulation of Pressure Effects on Self-Diffusion in BCC Metals

2008 ◽  
Vol 277 ◽  
pp. 125-132 ◽  
Author(s):  
Irina Valikova ◽  
Andrei V. Nazarov
Keyword(s):  
Atomic Structure ◽  
Diffusion Processes ◽  
Pressure Effects ◽  
Many Body ◽  
New Approach ◽  
Self Diffusion ◽  
Bcc Metals ◽  
Perfect System ◽  
Bcc Iron ◽  
And Migration

This work is devoted to the study of the point defect diffusion features in metals. In particular, we propose the model, which allows calculating activation volumes that describe the influence of pressure on the diffusion processes in solids. Our model realizes a new approach that makes it possible to self-consistently determine atomic structure near defect and constants characterizing the displacement of atoms in an elastic matrix around computational cell. Also we take into consideration that the energy of perfect system and system with a defect differently depends on the outer pressure, and this gives an addition to the values of migration and formation volumes. This addition can comprise a considerable part of activation volume. Moreover, we take into account that the atomic jump is a momentary process and so we carry out only partial relaxation of the atomic structure in the vicinity of a defect. The formation and migration energies and formation and migration volumes have been calculated for vacancies, di-vacancies and interstitials in bcc iron and tungsten using pair and many-body potentials.

scholarly journals Repulsion leads to coupled dislocation motion and extended work hardening in bcc metals

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
K. Srivastava ◽  
D. Weygand ◽  
D. Caillard ◽  
P. Gumbsch
Keyword(s):  
Work Hardening ◽  
Activation Barrier ◽  
Dislocation Motion ◽  
Dislocation Dynamics ◽  
Additional Contribution ◽  
High Symmetry ◽  
Screw Dislocations ◽  
Bcc Metals ◽  
Kink Pair ◽  
Extended Work

Abstract Work hardening in bcc single crystals at low homologous temperature shows a strong orientation-dependent hardening for high symmetry loading, which is not captured by classical dislocation density based models. We demonstrate here that the high activation barrier for screw dislocation glide motion in tungsten results in repulsive interactions between screw dislocations, and triggers dislocation motion at applied loading conditions where it is not expected. In situ transmission electron microscopy and atomistically informed discrete dislocation dynamics simulations confirm coupled dislocation motion and vanishing obstacle strength for repulsive screw dislocations, compatible with the kink pair mechanism of dislocation motion in the thermally activated (low temperature) regime. We implement this additional contribution to plastic strain in a modified crystal plasticity framework and show that it can explain the extended work hardening regime observed for [100] oriented tungsten single crystal. This may contribute to better understanding the increase in ductility of highly deformed bcc metals.

An Analysis of Lattice Dynamical Angular Force Models for Body Centered Cubic Metals

1979 ◽  
Vol 34 (6) ◽  
pp. 721-723
Author(s):  
R. N. Khanna ◽  
R. P. S. Rathore
Keyword(s):  
General Equilibrium ◽  
Pair Potential ◽  
Dynamical Behaviour ◽  
Body Centered Cubic ◽  
Axially Symmetric ◽  
Equilibrium Conditions ◽  
Central Pair ◽  
Electron Pressure ◽  
Cubic Metals ◽  
Bcc Metals

Abstract Present angular force models for lattice dynamical behaviour of body centered cubic (bcc) metals have been analysed for the satisfaction of rotational invariance and general equilibrium conditions. It has been found that most of the angular force models (except that due to Clark et al.) are deficient and leave the lattice under stress. Further it has been inferred that either the axially symmetric or the central pair potential schemes, incorporating the concept of electron pressure, provide the realistic picture of lattice excitations in metals.

scholarly journals Structure and dynamics of crowdion defects in bcc metals

2018 ◽  
Vol 03 (03n04) ◽  
pp. 1840003
Author(s):  
S. P. Fitzgerald
Keyword(s):  
Kinetic Monte Carlo ◽  
Coarse Grained ◽  
Nuclear Materials ◽  
Dislocation Loops ◽  
Cubic Metals ◽  
Bcc Metals ◽  
Diffusive Dynamics ◽  
Object Kinetic Monte Carlo ◽  
Barrier Problem ◽  
Kontorova Model

Crowdion defects are produced in body-centered-cubic metals under irradiation. Their structure and diffusive dynamics play a governing role in microstructural evolution, and hence the mechanical properties of nuclear materials. In this paper, we apply the analytical Frenkel-Kontorova model to crowdions and clusters thereof (prismatic dislocation loops) and show that the Peierls potential in which these defects diffuse is remarkably small (in the micro eV range as compared to the eV range for other defects). We also develop a coarse-grained statistical methodology for simulating these fast-diffusing objects in the context of object kinetic Monte Carlo, which is less vulnerable to the low barrier problem than naïve stochastic simulation.

scholarly journals Unusual activated processes controlling dislocation motion in body-centered-cubic high-entropy alloys

2020 ◽  
Vol 117 (28) ◽  
pp. 16199-16206 ◽  
Author(s):  
Bing Chen ◽  
Suzhi Li ◽  
Hongxiang Zong ◽  
Xiangdong Ding ◽  
Jun Sun ◽  
...  
Keyword(s):  
Activation Barrier ◽  
Dislocation Motion ◽  
Atomistic Simulations ◽  
High Entropy Alloys ◽  
Body Centered Cubic ◽  
Screw Dislocations ◽  
High Entropy ◽  
Bcc Metals ◽  
Edge Dislocations ◽  
Rate Limiting

Atomistic simulations of dislocation mobility reveal that body-centered cubic (BCC) high-entropy alloys (HEAs) are distinctly different from traditional BCC metals. HEAs are concentrated solutions in which composition fluctuation is almost inevitable. The resultant inhomogeneities, while locally promoting kink nucleation on screw dislocations, trap them against propagation with an appreciable energy barrier, replacing kink nucleation as the rate-limiting mechanism. Edge dislocations encounter a similar activated process of nanoscale segment detrapping, with comparable activation barrier. As a result, the mobility of edge dislocations, and hence their contribution to strength, becomes comparable to screw dislocations.

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