Grain Boundary Complexion Transitions

2020 ◽  
Vol 50 (1) ◽  
pp. 465-492 ◽  
Author(s):  
Patrick R. Cantwell ◽  
Timofey Frolov ◽  
Timothy J. Rupert ◽  
Amanda R. Krause ◽  
Christopher J. Marvel ◽  
...  
Keyword(s):  
Liquid Metal ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Bulk Composition ◽  
Polycrystalline Metals ◽  
Research Challenges ◽  
Rapid Changes ◽  
And Performance ◽  
Property Changes ◽  
Processing Properties

Grain boundaries can undergo phase-like transitions, called complexion transitions, in which their structure, composition, and properties change discontinuously as temperature, bulk composition, and other parameters are varied. Grain boundary complexion transitions can lead to rapid changes in the macroscopic properties of polycrystalline metals and ceramics and are responsible for a variety of materials phenomena as diverse as activated sintering and liquid-metal embrittlement. The property changes caused by grain boundary complexion transitions can be beneficial or detrimental. Grain boundary complexion engineering exploits beneficial complexion transitions to improve the processing, properties, and performance of materials. Here, we review the thermodynamic fundamentals of grain boundary complexion transitions, highlight the strongest experimental and computationalevidence for these transitions, clarify a number of important misconceptions, discuss the advantages of grain boundary complexion engineering, and summarize existing research challenges.

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.

scholarly journals Towards Understanding the Different Influences of Grain Boundaries on Ion Transport in Sulfide and Oxide Solid Electrolytes

2019 ◽  
Author(s):  
James Dawson ◽  
Pieremanuele Canepa ◽  
Matthew Clarke ◽  
Theodosios Famprikis ◽  
Dibyajyoti Ghosh ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Ion Transport ◽  
Grain Boundaries ◽  
Solid Electrolytes ◽  
Ionic Conductivities ◽  
Liquid Electrolyte ◽  
Boundary Resistance ◽  
Polycrystalline Materials ◽  
Solid State Batteries ◽  
And Performance

Solid electrolytes provide a route to the development of all-solid-state batteries that can potentially surpass the safety and performance of conventional liquid electrolyte-based devices. Sulfide solid electrolytes have received particular attention as a result of their high ionic conductivities. One of the main reasons for such high ionic conductivity is the apparently reduced grain boundary resistance of sulfide solid electrolytes compared to their oxide counterparts, but this is not fully established. Using two model electrolyte systems, Na3PS4 and Na3PO4, we apply a novel microscale simulation approach to analyze ionic transport in polycrystalline materials with various grain volumes. For Na3PO4, high grain boundary resistance is found, with the Na-ion conductivity decreasing with decreasing grain volume. For Na3PS4, the overall influence of grain boundaries is significantly reduced compared to the oxide. Detailed analysis reveals a minimal change in the local structures and Na-ion conduction mechanism between bulk and polycrystalline Na3PS4, whereas the change is far more substantial for Na3PO4, with evidence of over-coordination of Na ions at the grain boundaries. Our microscale approach helps to explain the fundamentally different influences of grain boundaries on ion transport in phosphate and thiophosphate solid electrolytes.

Quantitative measurements of stresses at grain boundaries in polycrystalline metals

1988 ◽  
Vol 46 ◽  
pp. 620-621
Author(s):  
W. A. T. Clark
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Direct Transmission ◽  
Static Mode ◽  
Quantitative Measurements ◽  
Polycrystalline Metals ◽  
Dynamic Studies ◽  
Pile Up ◽  
Mode A

It has long been recognized that the deformation of polycrystalline metals proceeds by the movement of individual dislocations both within the grains and across the grain boundaries which separate them. It is known, for example, that the yield stress is directly affected by the density of grain boundaries in a metal; in the familiar Hall-Petch relationship it is inversely proportional to the grain diameter. Various models have been proposed to account for this behaviour, all of which involve the interaction between dislocations and grain boundaries (for a review see e.g. ref. 1). Microscopically, these interactions can be accomplished by several different mechanisms, which include the nucleation of new dislocations, direct transmission of dislocations across the interface, the absorption and desorption of dislocations into and out of the interface.The TEM can be used for both static and in-situ dynamic studies of these interactions. In the static mode, a TEM is used to analyze fully the crystallography of dislocation pile-up/grain boundary interactions; one such pile-up is shown in Fig. 1.

Measurement of compositional changes accompanying solid-state transformations at grain boundaries in metals

1987 ◽  
Vol 45 ◽  
pp. 296-299
Author(s):  
Ernest L. Hall ◽  
Clyde L. Briant
Keyword(s):  
Solid State ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Precipitation Process ◽  
Second Phase ◽  
Slow Cooling ◽  
Collector Plate ◽  
Compositional Changes ◽  
Property Changes ◽  
Boundary Chemistry

In many multicomponent metallic systems, solid-state precipitation processes can occur upon slow cooling or isothermal aging of solutionized material. Frequently, the precipitates form at grain boundaries, which are preferred sites for the nucleation and growth of the second phase. The precipitates generally grow through a combination of matrix and grain boundary diffusion, in which the grain boundary acts as a collector plate for the delivery of the solute to the growing precipitate. The precipitation process is thus accompanied by significant changes in the chemistry of the grain boundary and matrix regions near the grain boundary. These grain boundary chemistry changes can have a profound effect on the macroscopic properties of the material, including corrosion resistance, strength, and ductility. In order to understand the mechanism associated with these property changes, it is necessary to obtain a complete and precise description of the magnitude and extent of the compositional changes which have occurred at the grain boundaries.

Towards Understanding the Different Influences of Grain Boundaries on Ion Transport in Sulfide and Oxide Solid Electrolytes

2019 ◽  
Author(s):  
James Dawson ◽  
Pieremanuele Canepa ◽  
Matthew Clarke ◽  
Theodosios Famprikis ◽  
Dibyajyoti Ghosh ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Ion Transport ◽  
Grain Boundaries ◽  
Solid Electrolytes ◽  
Ionic Conductivities ◽  
Liquid Electrolyte ◽  
Boundary Resistance ◽  
Polycrystalline Materials ◽  
Solid State Batteries ◽  
And Performance

Solid electrolytes provide a route to the development of all-solid-state batteries that can potentially surpass the safety and performance of conventional liquid electrolyte-based devices. Sulfide solid electrolytes have received particular attention as a result of their high ionic conductivities. One of the main reasons for such high ionic conductivity is the apparently reduced grain boundary resistance of sulfide solid electrolytes compared to their oxide counterparts, but this is not fully established. Using two model electrolyte systems, Na3PS4 and Na3PO4, we apply a novel microscale simulation approach to analyze ionic transport in polycrystalline materials with various grain volumes. For Na3PO4, high grain boundary resistance is found, with the Na-ion conductivity decreasing with decreasing grain volume. For Na3PS4, the overall influence of grain boundaries is significantly reduced compared to the oxide. Detailed analysis reveals a minimal change in the local structures and Na-ion conduction mechanism between bulk and polycrystalline Na3PS4, whereas the change is far more substantial for Na3PO4, with evidence of over-coordination of Na ions at the grain boundaries. Our microscale approach helps to explain the fundamentally different influences of grain boundaries on ion transport in phosphate and thiophosphate solid electrolytes.

Experimental and Simulation Insight on the Transport of Silver Fission Product in SiC

2008 ◽  
Author(s):  
Tyler J. Gerczak ◽  
Lizhen Tan ◽  
Todd R. Allen ◽  
Sarah Khalil ◽  
David Shrader ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Fission Product ◽  
Grain Boundaries ◽  
Diffusion Mechanism ◽  
Coincidence Site Lattice ◽  
Boundary Structure ◽  
Rate Equations ◽  
Triso Fuel ◽  
And Performance ◽  
Fuel Particles

Understanding of the fission product transport in TRISO fuel particles is fundamental to improving the safety and performance of high temperature gas cooled reactors. Previous experiments showing silver release from TRISO fuel have focused on release measurements and not direct observation of the fission product transport. The possible diffusion of Ag via a grain boundary diffusion mechanism is being examined. By characterizing the SiC grain boundary structure according the coincidence site lattice scheme and detecting diffusion along specific grain boundaries, insight into the relationship between SiC microstructure and Ag release may be obtained. In addition computer modeling is being used to investigate the diffusion of silver through SiC. We employ a multi-scale approach based on ab initio techniques, molecular dynamics, and continuum rate equations in order to establish relationships between complex microstructures and diffusion rates. Initial work has begun on transport through bulk SiC and on building realistic models of grain boundaries in SiC.

Liquid Metal Penetration along Grain Boundaries

1994 ◽  
Vol 343 ◽  
Author(s):  
V. E. Fradkov
Keyword(s):  
Liquid Metal ◽  
Grain Boundary ◽  
Equilibrium State ◽  
Grain Boundaries ◽  
Constant Velocity ◽  
Liquid Solution ◽  
Dihedral Angles ◽  
L System

ABSTRACTLiquid metal grain boundary corrosion is discussed in terms of grain boundary etching profiles with equilibrium dihedral angles at the vertex of the grooves close to zero. It is shown that if the liquid solution is in equilibrium with the solid, then only grain boundary grooving occurs, producing small grooves growing in time as t½. However, if the equilibrium cannot be reached, a long liquid filled canal develops along the grain boundary, rapidly propagating with constant velocity. To stop such rapid grain boundary corrosion certain measures should be taken to reach the equilibrium state. This explains, for example, why removal of oxygen from the Nb(s)-Li(l) system prevents rapid grain boundary corrosion of Nb.

Measurement of the Displacement Across a Coincidence Grain Boundary

1977 ◽  
Vol 35 ◽  
pp. 124-125
Author(s):  
J. W. Matthews ◽  
W. M. Stobbs
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Fault ◽  
The Other ◽  
Measuring Technique ◽  
High Angle ◽  
Twin Boundaries ◽  
Rigid Displacement ◽  
Cubic Crystals ◽  
Lattice Displacement

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

Observations of dislocation interactions with recrystallized grain boundaries

1988 ◽  
Vol 46 ◽  
pp. 628-629
Author(s):  
C. W. Price
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Dislocation Structure ◽  
Hot Deformation ◽  
Static Recrystallization ◽  
High Dislocation Density ◽  
High Angle ◽  
Dislocation Interactions

Little evidence exists on the interaction of individual dislocations with recrystallized grain boundaries, primarily because of the severely overlapping contrast of the high dislocation density usually present during recrystallization. Interesting evidence of such interaction, Fig. 1, was discovered during examination of some old work on the hot deformation of Al-4.64 Cu. The specimen was deformed in a programmable thermomechanical instrument at 527 C and a strain rate of 25 cm/cm/s to a strain of 0.7. Static recrystallization occurred during a post anneal of 23 s also at 527 C. The figure shows evidence of dissociation of a subboundary at an intersection with a recrystallized high-angle grain boundary. At least one set of dislocations appears to be out of contrast in Fig. 1, and a grainboundary precipitate also is visible. Unfortunately, only subgrain sizes were of interest at the time the micrograph was recorded, and no attempt was made to analyze the dislocation structure.

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