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.

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).

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.

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.

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.

The recrystallization process in some polycrystalline metals

1962 ◽  
Vol 267 (1328) ◽  
pp. 11-30 ◽  
Keyword(s):  
Activation Energy ◽  
Electron Microscope ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Migration ◽  
Grain Boundary Migration ◽  
Recrystallization Process ◽  
Boundary Mobility ◽  
Grain Boundary Mobility ◽  
Polycrystalline Metals

Electron microscope observations on some polycrystalline metals suggest that after small to moderate deformation, recrystallization occurs by the migration of the original grain boundaries. A theory based on this mechanism can account for the known form of the recrystallization kinetics without necessarily introducing any anisotropy of grain boundary mobility. For this mechanism the so-called recrystallization activation energy is identical to the activation energy for grain boundary migration.

The Influence of Grain Boundary Migration on the Diffusion Behaviour of Thin Films

1980 ◽  
Vol 35 (6) ◽  
pp. 613-618
Author(s):  
E. Ehrmann-Falkenau ◽  
A. Wagendristel
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Migration ◽  
Boundary Surface ◽  
Depth Profiling ◽  
Lattice Diffusion ◽  
Grain Boundary Migration ◽  
Order Of Magnitude ◽  
Diffusion Behaviour

Simultaneous grain boundary-, surface- and lattice diffusion in hypothetical thin film couples of miscible components was computer simulated. On this basis the diffusion into fixed and moving grain boundaries is discussed with respect to the determination of diffusivities by depth profiling methods. The data evaluated from the synthesised depth profiles according to Whipple-Le Claire as well as to Gilmer and Farrell were compared with the diffusivities used for the computation. Agreement was found for systems with a fixed grain boundary network. Moving grain boundaries, however, may cause errors of an order of magnitude towards lower grain boundary diffusivities

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