Migrating Interfaces in Sapphire Bicrystals and Tricrystals

2000 ◽  
Vol 6 (S2) ◽  
pp. 386-387
Author(s):  
N. Ravishankar ◽  
M.T. Johnson ◽  
C. Barry Carter
Keyword(s):  
Mass Transport ◽  
Liquid Film ◽  
Grain Boundaries ◽  
Ostwald Ripening ◽  
Chemical Potential ◽  
Driving Forces ◽  
Boundary Migration ◽  
Liquid Phase Sintering ◽  
Polycrystalline Materials ◽  
Second Phase

The migration of grain boundaries in polycrystalline materials can occur under a variety of driving forces. Grain growth in a single-phase material and Ostwald ripening of a second phase are two common processes involving boundary migration. The mass transport in each of these cases can be related to a chemical potential difference across the grains; due to curvature in the former case and due to a difference in the chemistry in the latter case. The mass transport across grains controls the densification process during sintering. In the case of liquid-phase sintering (LPS), a liquid film may be present at the grain boundaries which results in an enhanced mass transport between grains leading to faster densification. Hence, in LPS, it is important to understand mass transport across and along a boundary containing a liquid film. The use of bicrystals and tricrystals with glass layers in the boundary can provide a controlled geometry by which to study this phenomenon.

Effect of mass transport along interfaces and grain boundaries on copper interconnect degradation

2004 ◽  
Vol 812 ◽  
Author(s):  
Ehrenfried Zschech ◽  
Moritz A. Meyer ◽  
Eckhard Langer
Keyword(s):  
Mass Transport ◽  
Grain Boundaries ◽  
Void Formation ◽  
Degradation Process ◽  
Copper Interconnects ◽  
Second Phase ◽  
Copper Interconnect ◽  
Void Evolution ◽  
Two Phases

AbstractIn-situ SEM electromigration studies were performed at fully embedded via/line interconnect structures to visualize the time-dependent void evolution in inlaid copper interconnects. Void formation, growth and movement, and consequently interconnect degradation, depend on both interface bonding and copper microstructure. Two phases are distinguished for the electromigration-induced interconnect degradation process: In the first phase, agglomerations of vacancies and voids are formed at interfaces and grain boundaries, and voids move along weak interfaces. In the second phase of the degradation process, they merge into a larger void which subsequently grows into the via and eventually causes the interconnect failure. Void movement along the copper line and void growth in the via are discontinuous processes, whereas their step-like behavior is caused by the copper microstructure. Directed mass transport along inner surfaces depends strongly on the crystallographic orientation of the copper grains. Electromigration lifetime can be drastically increased by changing the copper/capping layer interface. Both an additional CoWP coating and a local copper alloying with aluminum increase the bonding strength of the top interface of the copper interconnect line, and consequently, electromigration-induced mass transport and degradation processes are reduced significantly.

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.

TEM Analysis of an Alumina Bicrystal Section Using a Fib

2001 ◽  
Vol 7 (S2) ◽  
pp. 326-327
Author(s):  
Jeffrey K. Fairer ◽  
N. Ravishankar ◽  
Joseph R. Michael ◽  
C. Barry Carter
Keyword(s):  
Liquid Phase ◽  
Mass Transport ◽  
Binary Phase Diagram ◽  
Boundary Migration ◽  
Liquid Phase Sintering ◽  
Grain Boundary Migration ◽  
Tem Analysis ◽  
Sem Image ◽  
Polycrystalline Ceramic ◽  
Polycrystalline Ceramic Material

Grain boundary migration (GBM) during the sintering and densification of a polycrystalline ceramic material occurs as a result of mass transport across an interface. When there is a liquid film present, either due to additives used for liquid-phase sintering or unavoidable impurities in the material, the mass transport can be visualized in terms of dissolving material from one grain and precipitating it on another. in order to study the effects of crystallography on GBM in the presence of a liquid phase, alumina bicrystals have been fabricated with anorthite (CaA12Si208) glass films at the interface. The alumina-anorthite system in a bicrystal geometry is used because the pseudo-binary phase diagram of the system is well known, the bicrystal geometry allows for control over the original interface misorientation, and the glassy phase of anorthite is the most commonly occurring glass in commercially used alumina.Fig. 1 is a secondary-electron SEM image of an alumina bicrystal recorded using a field-emission SEM (Hitachi S900) operating at 5 kV.

An Overview of Accomplishments and Challenges in Recrystallization and Grain Growth

2007 ◽  
Vol 558-559 ◽  
pp. 33-42 ◽  
Author(s):  
Anthony D. Rollett ◽  
Abhijit P. Brahme ◽  
C.G. Roberts
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Degrees Of Freedom ◽  
Driving Forces ◽  
Excess Free Energy ◽  
Abnormal Grain Growth ◽  
Process Models ◽  
Three Dimensions ◽  
Polycrystalline Materials ◽  
General Process

The study of microstructural evolution in polycrystalline materials has been active for many decades so it is interesting to illustrate the progress that has been made and to point out some remaining challenges. Grain boundaries are important because their long-range motion controls evolution in many cases. We have some understanding of the essential features of grain boundary properties over the five macroscopic degrees of freedom. Excess free energy, for example, is dominated by the two surfaces that comprise the boundary although the twist component also has a non-negligible influence. Mobility is less well defined although there are some clear trends for certain classes of materials such as fcc metals. Computer simulation has made a critical contribution by showing, for example, that mobility exhibits an intrinsic crystallographic anisotropy even in the absence of impurities. At the mesoscopic level, we now have rigorous relationships between geometry and growth rates for individual grains in three dimensions. We are in the process of validating computer models of grain growth against 3D non-destructive measurements. Quantitative modeling of recrystallization that includes texture development has been accomplished in several groups. Other properties such as corrosion resistance are being related quantitatively to microstructure. There remain, however, numerous challenges. Despite decades of study, we still do not have complete cause-and-effect descriptions of most cases of abnormal grain growth. The response of nanostructured materials to annealing can lead to either unexpected resistance to coarsening, or, coarsening at unexpectedly low temperatures. General process models for recrystallization that can be applied to industrial alloys remain elusive although significant progress has been made for the specific case of aluminum alloy processing. Thin films often exhibit stagnation of grain growth that we do not fully understand, as well as abnormal grain growth. Grain boundaries respond to driving forces in more complicated ways than we understood. Clearly many exciting challenges remain in grain growth and recrystallization.

SEM-ECP Analysis of Grain-Boundary Character Distribution in Polycrystalline Materials

1996 ◽  
Vol 54 ◽  
pp. 354-355
Author(s):  
Tadao Watanabe
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Migration ◽  
Polycrystalline Materials ◽  
Grain Boundary Character Distribution ◽  
Boundary Character ◽  
Grain Boundary Character ◽  
Character Distribution ◽  
Boundary Character Distribution

As demonstrated early 1980’s (1), the scanning electron rnicrocopy-electron channelling pattern (SEM-ECP) technique is very powerful in determination of orientation of individual grains and the character of grain boundaries in polycrystalline materials. Figure 1(a) and (b) show SEM and ECP images of a grain boundary in polycrystal line iron-6.5 mass % silicon ribbon produced by rapid solidification and subsequent annealing. We can intuitively recognize from the SEM-ECP image that the character of the boundary is of <100> tilt type with about 7° misorientation angle. This kind of direct observation is very useful for a study of grain boundary migration and grain growth.This paper discusses advantages of the SEM-ECP technique for the precise determination of the character of grain boundary and for statistical analysis of grain boundaries to bridge roles of individual grain boundaries and bulk properties in a polycrystal. The new microstructural parameter associated with grin boundary termed “grain boundary character distribution (GBCD)” which was introduced by the present author (2,3) and has been utilized in designing and engineering grain boundaries in order to produce desirable and/or high bulk performance in polycrystalline materials (4,5). GBCD describes the type and the frequency of different types of grain boundaries, ie. random general boundaries and special boundaries like low-angle boundaries and low Σ coincidence boundaries.

Microstructure through an Ice Sheet

2013 ◽  
Vol 753 ◽  
pp. 481-484 ◽  
Author(s):  
Tobias Binder ◽  
Ilka Weikusat ◽  
Johannes Freitag ◽  
Christoph S. Garbe ◽  
Dietmar Wagenbach ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Driving Forces ◽  
Boundary Migration ◽  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Grain Size Analysis ◽  
Size Analysis

Ice cores through an ice sheet can be regarded as a sample of a unique natural deformation experiment lasting up to a million years. Compared to other geological materials forming the earth‘s crust, the microstructure is directly accessible over the full depth. Controlled sublimation etching of polished ice sections reveals pores, air bubbles, grain boundaries and sub-grain boundaries at the surface. The microstructural features emanating at the surface are scanned. A dedicated method of digital image processing has been developed to extract and characterize the grain boundary networks. First preliminary results obtained from an ice core drilled through the Greenland ice sheet are presented. We discuss the role of small grains in grain size analysis and derive from the shape of grain boundaries the acting driving forces for grain boundary migration.

Anhysteretic magnetization processes in multidomain crystals and polycrystals

1969 ◽  
Vol 313 (1512) ◽  
pp. 97-116 ◽  
Keyword(s):  
Grain Boundaries ◽  
Minimum Energy ◽  
Polycrystalline Materials ◽  
Second Phase ◽  
Magnetization Curves ◽  
Plane Parallel ◽  
Domain Structures ◽  
Model Domain ◽  
Oriented Polycrystalline ◽  
Anhysteretic Magnetization

Theoretical anhysteretic magnetization curves are derived by searching for the minimum energy in an applied field of model domain structures. Magnetization curves are derived for: (1) Finite uniaxial crystals with 180° plane parallel walls. (2) Slightly misoriented polycrystals with (a) plane parallel walls, (b) walls allowed to bow. (3) Oriented polycrystalline materials with air gaps at the grain boundaries. The third model is found to be unrealistic, for a polycrystalline material without any second phase at the grain boundaries, and it is shown that the observed magnetization behaviour may be more generally accounted for in terms of the misorientation between grains. The calculations are precise, but the results are dependent on the initial choice of model domain structure and any limitations imposed on the way in which the walls move.

Abnormal Grain Coarsening and Its Possible Relationship with Particle Limited Normal Grain Coarsening

2004 ◽  
Vol 467-470 ◽  
pp. 843-852 ◽  
Author(s):  
Roger D. Doherty ◽  
Elizabeth Hoffman ◽  
Christopher Hovanec ◽  
Arnaud Lens
Keyword(s):  
Grain Boundaries ◽  
High Purity ◽  
Volume Fraction ◽  
Boundary Migration ◽  
Second Phase ◽  
Grain Coarsening ◽  
Grain Sizes ◽  
Second Phase Particles ◽  
Prior Literature ◽  
Small Grains

The prior literature on abnormal grain coarsening (AGC) at low volume fractions (f) of stable second phase particles in high purity Al alloys is reviewed and reanalyzed in the light of developments in modeling particle inhibition of grain boundary migration. With the usual assumptions (i) of incoherent particles that retain their shape on contact with the grain boundaries and (ii) that all the grain boundaries are equally mobile, it appears impossible to account for process of AGC. Normal grain coarsening (NGC) is shown to be less inhibited by the particles than is AGC. This idea is explored using a new but simple model of particle inhibition by curvature removal. The curvature of the smallest grains is always larger than that of the larger grains. Two possible hypotheses to overcome this difficulty are proposed: First the possible change of shape of particles on slowly moving grain boundaries, of grains with near 14 neighbors should, after a small increment of NGC, promote AGC at low values of the volume fraction f. The second hypothesis involves the observed high density of immobile, low angle grain boundaries (LAGBs) found in recent experiments on high purity Al-Fe-Si alloys cast with very coarse grain sizes. These alloys undergo rapid AGC even at higher values of f (> 0.01). These LAGBs are expected to inhibit the shrinkage of many of the small grains, whose loss is the fundamental mechanism of NGC.

Simulation of Recrystallization Using Molecular Dynamics; Effects of the Interatomic Potential

2007 ◽  
Vol 558-559 ◽  
pp. 1081-1086 ◽  
Author(s):  
Rasmus B. Godiksen ◽  
Zachary T. Trautt ◽  
Moneesh Upmanyu ◽  
Søren Schmidt ◽  
Dorte Juul Jensen
Keyword(s):  
Molecular Dynamics ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Interatomic Potential ◽  
Driving Forces ◽  
Boundary Migration ◽  
Grain Boundary Migration ◽  
High Angle ◽  
Embedded Atom ◽  
Atomic Interactions

Recrystallization is governed by the migration of high angle grain boundaries traveling through a deformed material driven by the excess energy located primarily in dislocation structures. A method for investigating the interaction between a migrating grain boundary and dislocation boundaries using molecular dynamics (MD) was recently developed. During simulations migrating high angle grain boundaries interact with dislocation boundaries, and individual dislocations from the dislocation boundaries are absorbed into the grain boundaries. Results obtained previously, using a simple Lennard-Jones (LJ) potential, showed surprisingly irregular grain boundary migration compared to simulations of grain boundary migration applying other types of driving forces. Inhomogeneous boundary-dislocation interactions were also observed in which the grain boundaries locally acquired significant cusps during dislocation absorption events. The study presented here makes comparisons between simulations performed using a LJ- and an embedded atom method (EAM) aluminum potential. The results show similarities which indicate that it is the crystallographic features rather than the atomic interactions that determine the details of the migration process.

Influence of Crystallographic Orientation, Chemical Inhomogeneities, Material Transport Anisotropy and Elastic Strain Energy on the Migration of Grain Boundaries in Chromium-Doped Alumina During Internal Reduction

1994 ◽  
Vol 357 ◽  
Author(s):  
Monika Backhaus-Ricoult ◽  
A. Peyrot-Chabrol ◽  
R. Chiron ◽  
S. Hagege
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Elastic Strain ◽  
Strain Energy ◽  
Chemical Potential ◽  
Boundary Migration ◽  
Elastic Strain Energy ◽  
Lattice Diffusion ◽  
Boundary Plane ◽  
Material Transport

AbstractDiffusion-induced grain boundary migration is observed during internal reduction of chromium-doped alumina. It occurs because grain boundary diffusion is fast compared to lattice diffusion of oxygen. The oxygen chemical potential relaxes between grain boundaries and adjacent grains. Migration to either side of the boundary is controlled by multiple factors: chemical composition differences between adjacent grains, elastic strain energy differences on the two sides of the boundary plane or by more rapid oxygen relaxation when the c-axis of a grain is perpendicular to the boundary plane.

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