scholarly journals Regularities of Structural Rearrangements in Single- and Bicrystals Near the Contact Zone

2020 ◽  
pp. 301-322
Author(s):  
Konstantin P. Zolnikov ◽  
Dmitrij S. Kryzhevich ◽  
Aleksandr V. Korchuganov
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Contact Zone ◽  
Boundary Migration ◽  
Shear Loading ◽  
Structural Defects ◽  
Grain Boundary Migration ◽  
Boundary Motion ◽  
Symmetric Tilt ◽  
Grain Boundary Motion

AbstractThe chapter is devoted to the analysis of the features of local structural rearrangementsin nanostructured materialsunder shear loadingand nanoindentation. The study was carried out using molecular dynamics-based computer simulation. In particular, we investigated the features of symmetric tilt grain boundary migration in bcc and fcc metals under shear loading. The main emphasis was on identifying atomic mechanisms responsible for the migration of symmetric tilt grain boundaries. We revealed that grain boundaries of this type can move with abnormally high velocities up to several hundred meters per second. The grain boundary velocity depends on the shear rate and grain boundary structure. It is important to note that the migration of grain boundary does not lead to the formation of structural defects. We showed that grain boundary moves in a pronounced jump-like manner as a result of a certain sequence of self-consistent displacements of grain boundary atomic planes and adjacent planes. The number of atomic planes involved in the migration process depends on the structure of the grain boundary. In the case of bcc vanadium, five planes participate in the migration of the Σ5(210)[001] grain boundary, and three planes determine the Σ5(310)[001] grain boundary motion. The Σ5(310)[001] grain boundary in fcc nickel moves as a result of rearrangements of six atomic planes. The stacking order of atomic planes participating in the grain boundary migration can change. A jump-like manner of grain boundary motion may be divided into two stages. The first stage is a long time interval of stress increase during shear loading. The grain boundary is motionless during this period and accumulates elastic strain energy. This is followed by the stage of jump-like grain boundary motion, which results in rapid stress drop. The related study was focused on understanding the atomic rearrangements responsible for the nucleation of plasticity near different crystallographic surfaces of fcc and bcc metals under nanoindentation. We showed that a wedge-shaped region, which consists of atoms with a changed symmetry of the nearest environment, is formed under the indentation of the (001) surface of the copper crystallite. Stacking faults arise in the (111) atomic planes of the contact zone under the indentation of the (011) surface. Their escape on the side free surface leads to a step formation. Indentation of the (111) surface is accompanied by nucleation of partial dislocations in the contact zone subsequent formation of nanotwins. The results of the nanoindentation of bcc iron bicrystal show that the grain boundary prevents the propagation of structural defects nucleated in the contact zone into the neighboring grain.

Grain Boundary Migration and Compensation Effect

2007 ◽  
Vol 550 ◽  
pp. 387-392
Author(s):  
Pavel Lejček
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Compensation Effect ◽  
Activation Enthalpy ◽  
Boundary Migration ◽  
Grain Boundary Migration ◽  
Boundary Motion ◽  
Exponential Factor ◽  
Grain Boundary Motion

Anisotropy of grain boundary motion in a Fe–6at.%Si alloy is represented by a spectrum of values of the activation enthalpy of migration and the pre-exponential factor, depending on the orientation of individual grain boundaries. The general plot of these values exhibits a pronounced linear interdependence called the compensation effect. It is shown that changes of these values, caused by changes of intensive variables, are thermodynamically consistent.

Phenomenology of shear-coupled grain boundary motion in symmetric tilt and general grain boundaries

2013 ◽  
Vol 61 (4) ◽  
pp. 1048-1060 ◽  
Author(s):  
Eric R. Homer ◽  
Stephen M. Foiles ◽  
Elizabeth A. Holm ◽  
David L. Olmsted
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Motion ◽  
Symmetric Tilt ◽  
Grain Boundary Motion

X-Ray Method for Continuous Tracking of Grain Boundary Motion: Investigation of Grain Boundary Migration in Al-Bicrystals

1994 ◽  
Vol 157-162 ◽  
pp. 125-130
Author(s):  
U. Czubayko ◽  
Dmitri A. Molodov ◽  
B.-C. Petersen ◽  
Günter Gottstein ◽  
Lasar S. Shvindlerman
Keyword(s):  
Grain Boundary ◽  
Boundary Migration ◽  
Grain Boundary Migration ◽  
Boundary Motion ◽  
Ray Method ◽  
X Ray ◽  
Grain Boundary Motion

Measurement of solute segregation to grain boundaries in the AEM: A review

1988 ◽  
Vol 46 ◽  
pp. 606-607
Author(s):  
D. B. Williams ◽  
A. D. Romig
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Migration ◽  
Grain Boundary Migration ◽  
Boundary Misorientation ◽  
Collector Plate ◽  
Segregation Process ◽  
Grain Boundary Misorientation ◽  
Structure Boundary ◽  
Equilibrium Segregation

The segregation of solute or imparity elements to grain boundaries can occur by three well-defined processes. The first is Gibbsian segregation in which an element of minimal matrix solubility confines itself to a monolayer at the grain boundary. Classical examples include Bi in Cu and S or P in Fe. The second process involves the depletion of excess matrix solute by volume diffusion to the boundary. In the boundary, the solute atoms diffuse rapidly to precipitates, causing them to grow by the ‘collector-plate mechanism.’ Such grain boundary diffusion is thought to initiate “Diffusion-Induced Grain Boundary Migration,” (DIGM). This process has been proposed as the origin of eutectoid transformations or discontinuous grain boundary reactions. The third segregation process is non-equilibrium segregation which result in a solute build-up around the boundary because of solute-vacancy interactions.All of these segregation phenomena usually occur on a sub-micron scale and are often affected by the nature of the grain boundary (misorientation, defect structure, boundary plane).

Domain coarsening by grain boundary migration in ordered Ni4Mo

1986 ◽  
Vol 44 ◽  
pp. 560-561
Author(s):  
K. Vasudevan ◽  
H. P. Kao ◽  
C. R. Brooks ◽  
E. E. Stansbury
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Short Range ◽  
Boundary Migration ◽  
Grain Boundary Migration ◽  
Rapid Cooling ◽  
Temperature Range ◽  
Fee Structure ◽  
Domain Coarsening ◽  
Boundary Reaction

The Ni4Mo alloy has a short-range ordered fee structure (α) above 868°C, but transforms below this temperature to an ordered bet structure (β) by rearrangement of atoms on the fee lattice. The disordered α, retained by rapid cooling, can be ordered by appropriate aging below 868°C. Initially, very fine β domains in six different but crystallographically related variants form and grow in size on further aging. However, in the temperature range 600-775°C, a coarsening reaction begins at the former α grain boundaries and the alloy also coarsens by this mechanism. The purpose of this paper is to report on TEM observations showing the characteristics of this grain boundary reaction.

FRACTAL GRAIN BOUNDARY MIGRATION

Fractals ◽  
2000 ◽  
Vol 08 (02) ◽  
pp. 189-194 ◽  
Author(s):  
MIKI TAKAHASHI ◽  
HIROYUKI NAGAHAMA
Keyword(s):  
Grain Boundary ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Boundary Migration ◽  
Empirical Relationship ◽  
Grain Boundary Migration ◽  
Dynamics Model ◽  
Cell Dynamics ◽  
Hollomon Parameter ◽  
Dimension Analysis

Fractal analysis on experimentally recrystallized quartz grain boundaries has been employed to relate the grain boundary complexities with deformation conditions, such as strain rate and temperature. The fractal dimensional increment of the grain boundaries, defined as (D-1), and the degree of irregularity in grain boundaries, is proportional to the logarithmic of the Zener–Hollomon parameter that is defined by strain rate and temperature (the Arrhenius term). The physical mean of the empirical relationship can be explained theoretically by a new grain boundary migration model (GBM or cell dynamics model) extended by the fractal concepts and the dimension analysis. This is a more general model than the migration growth model for the fractal grain boundaries.

scholarly journals Microstructural Evidence for Grain Boundary Migration and Dynamic Recrystallization in Experimentally Deformed Forsterite Aggregates

Minerals ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 17
Author(s):  
Caroline Bollinger ◽  
Billy Nzogang ◽  
Alexandre Mussi ◽  
Jérémie Bouquerel ◽  
Dmitri Molodov ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Dynamic Recrystallization ◽  
Grain Boundaries ◽  
Driving Forces ◽  
Electron Backscatter Diffraction ◽  
Boundary Migration ◽  
Large Strains ◽  
Grain Boundary Migration ◽  
Mapping Techniques ◽  
Von Mises

Plastic deformation of peridotites in the mantle involves large strains. Orthorhombic olivine does not have enough slip systems to satisfy the von Mises criterion, leading to strong hardening when polycrystals are deformed at rather low temperatures (i.e., below 1200 °C). In this study, we focused on the recovery mechanisms involving grain boundaries and recrystallization. We investigated forsterite samples deformed at large strains at 1100 °C. The deformed microstructures were characterized by transmission electron microscopy using orientation mapping techniques (ACOM-TEM). With this technique, we increased the spatial resolution of characterization compared to standard electron backscatter diffraction (EBSD) maps to further decipher the microstructures at nanoscale. After a plastic strain of 25%, we found pervasive evidence for serrated grain and subgrain boundaries. We interpreted these microstructural features as evidence of occurrences of grain boundary migration mechanisms. Evaluating the driving forces for grain/subgrain boundary motion, we found that the surface tension driving forces were often greater than the strain energy driving force. At larger strains (40%), we found pervasive evidence for discontinuous dynamic recrystallization (dDRX), with nucleation of new grains at grain boundaries. The observations reveal that subgrain migration and grain boundary bulging contribute to the nucleation of new grains. These mechanisms are probably critical to allow peridotitic rocks to achieve large strains under a steady-state regime in the lithospheric mantle.

Dynamical Simulation of the Motion of Curved Grain Boundaries Composed of Pyramidal-Shaped Ledges

1990 ◽  
Vol 193 ◽  
Author(s):  
Re-Jhen Jhan ◽  
P. D. Bristowe
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Migration ◽  
Model System ◽  
The Other ◽  
Grain Boundary Migration ◽  
Dynamical Simulation ◽  
Atomic Mechanism ◽  
Or Groups

ABSTRACTA dynamical simulation of curved grain boundaries composed of pyramidal-shaped ledges has shown that the boundaries can move by local conservative shuffles of atoms or groups of atoms such that one adjoining crystal grows at the expense of the other. In the model system studied, the shuffles often take the form of correlated rotational displacements about the axis normal to the boundary. The simulations provide support for the atomic mechanism proposed by Babcock and Balluffi to explain their observation of grain boundary migration without the participation of SGBDs.

In Situ EBSP Observations of Recrystallization in Commercial Purity Aluminum

2007 ◽  
Vol 558-559 ◽  
pp. 223-228 ◽  
Author(s):  
Katsura Kajihara
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Early Stage ◽  
Boundary Motion ◽  
Commercial Purity ◽  
Solute Content ◽  
In Situ Observations ◽  
Commercial Purity Aluminum ◽  
Grain Boundary Motion

This study presents in-situ EBSP observations of recrystallization in commercial purity aluminum sheets with different concentrations of solutes and different states of precipitation. The in-situ observations demonstrate clearly the behaviors of the nucleation and growth of recrystallized grains, and the movements of grain boundaries at an early stage of recrystallization. The high mobility of grain boundaries neighboring the deformed matrix was generally observed presumably due to strain-induced grain boundaries migration. The grain boundary motion was also found to strongly depend to the solute content level. These in-situ observations provide important evidence to show that the behaviors of grain boundary motion at an early stage of recrystallization leads to the grain size distribution and the curvature of grain boundaries after the primary recrystallization.

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