Grain Boundary Chemistry and Reactions in Metals

MRS Bulletin ◽  
1990 ◽  
Vol 15 (10) ◽  
pp. 26-32 ◽  
Author(s):  
C.L. Briant
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Materials Science ◽  
Bulk Material ◽  
Polished Cross Section ◽  
Nucleation Sites ◽  
Two Phases ◽  
The Individual ◽  
Individual Grains ◽  
Boundary Chemistry

An interface can be defined as a surface that serves as a common boundary between two phases. Examples include the boundaries between two solids, two immiscible liquids, a solid and a liquid, a solid and a gas, and a liquid and a gas. Interfaces have been studied for decades by scientists of many different disciplines. One reason for this interest is that the atomic structure and the chemical composition at the interface can differ from that of the bulk material on either side of it. Consequently, the properties of the interface can differ greatly from those of either bulk phase, and chemical reactions can occur more readily at the interface than in the bulk.All the interfaces listed in the previous paragraph are of interest to materials scientists. However, this article will only consider the grain boundary because it has received the most attention by researchers in materials science. Furthermore, we will only consider grain boundaries in metals; nonmetallic systems will be covered in other articles in this issue.A grain boundary is an interface that exists where two single crystals are joined in such a way that their crystallographic orientations are not completely matched. Thus, any polycrystalline material contains many grain boundaries. They occur wherever the individual grains meet one another and can usually be observed by etching a polished cross section of the surface as shown in Figure 1. Grain boundaries first form in a metal as a result of the multiple nucleation sites that occur during solidification.

Athermal Motion of Grain Boundaries, Twins and Triple Junctions in Zn

2004 ◽  
Vol 467-470 ◽  
pp. 801-806 ◽  
Author(s):  
Vera G. Sursaeva
Keyword(s):  
Thermal Expansion ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Triple Junction ◽  
Triple Junctions ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
The Difference ◽  
The Individual ◽  
Individual Grains

When a bicrystal or polycrystal are subjected to a change in temperature, the individual responses of the two adjoining crystals may differ in a manner, which tends to produce a dilatational mismatch along grain boundaries. If compatibility is to be retained along the interface, an additional set of stresses must then be generated in order to conserve this compatibility. ‘Compatibility stresses’ will also be generated whenever a polycrystal is heated or cooled and the thermal expansion coefficients of the individual grains are different due to thermal expansion anisotropy. In such cases adjacent grains will attempt to change dimensions and develop mismatches by amounts controlled by the parameter Δa*ΔΤ, where Δa is the difference between the thermal expansion coefficients in the appropriate directions, and ΔΤ is the temperature change. These ‘compatibility stresses’ may be relieves if grain boundary motion, triple junction migration and grain growth are possible. These ‘compatibility stresses’ may play important role in the kinetic behavior of the microstructure ranging from influencing the behavior of lattice dislocations near the grain boundaries to promoting grain boundary and triple junction dragging or moving. The motion of the ‘special’ grain boundaries, triple junctions with ‘special’ grain boundaries and twins under the influence of internal mechanical stresses is the main subject of this paper.

scholarly journals High Resolution Electron Microscopy of Grain Boundaries in Nanophase Palladium

1989 ◽  
Vol 153 ◽  
Author(s):  
G. J. Thomas ◽  
R. W. Siegel ◽  
J. A. Eastman
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Lattice Structure ◽  
High Resolution Electron Microscopy ◽  
Coarse Grained ◽  
Resolution Electron ◽  
The Individual ◽  
Individual Grains

AbstractUsing high resolution electron microscopy, consolidated nanophase palladium samples were examined following electrolytic thinning after a hydriding - dehydriding cycle at 310 K. Due to the small size and random orientations of the individual grains, a large number of grain boundaries were available for examination. Some of these yielded adequate imaging conditions to allow observation of the lattice structure in the grain boundary regions. Image simulations were performed to determine the sensitivity of the technique to lattice disorder. The results of these studies suggest that grain boundary structures in nanophase palladium are similar to those in conventional coarse-grained polycrystals.

scholarly journals Image Simulations of Ge Twin Boundaries.

1992 ◽  
Vol 295 ◽  
Author(s):  
Stuart Mckernan ◽  
C. Barry Carter
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
High Angle ◽  
Structural Units ◽  
Twin Boundaries ◽  
Large Unit ◽  
Unit Cells ◽  
The Individual ◽  
Image Simulations

AbstractGeneral high-angle tilt grain boundaries may be described by an arrangement of repeating structural units. Some grain-boundary defects may also be modeled by the incorporation of structural units of related boundary structures into the boundary. The simulation of these structures requires the use of prohibitively large unit cells. The possibility of modeling these boundaries by the superposition of image simulations of the individual structural units isinvestigated.

Atomic Scale Analysis of a YSZ Bicrystal Grain Boundary

2001 ◽  
Vol 7 (S2) ◽  
pp. 400-401
Author(s):  
Y. Lei ◽  
Y. Ito ◽  
N. D. Browning
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Bulk Material ◽  
Atomic Scale ◽  
Structure Property ◽  
Contrast Imaging ◽  
Structure Property Relationships ◽  
Commercial Applications ◽  
Z Contrast ◽  
Electron Energy Loss

Yttria-stabilized zirconia (YSZ) has been the subject of many experimental and theoretical studies, due to the commercial applications of zirconia-based ceramics in solid state oxide fuel cells. Since the grain boundaries usually dominate the overall macroscopic performance of the bulk material, it is essential to develop a fundamental understanding of their structure-property relationships. Previous research has been performed on the atomic structure of grain boundaries in YSZ, but no precise atomic scale compositional and chemistry characterization has been carried out. Here we report a detailed analytical study of an [001] symmetric 24° bicrystal tilt grain boundary in YSZ prepared with ∼10 mol % Y2O3 by Shinkosha Co., Ltd by the combination of Z-contrast imaging and electron energy loss spectroscopy (EELS).The experimental analysis of the YSZ sample was carried out on a 200kV Schottky field emission JEOL 201 OF STEM/TEM4.

Nanometer Scale Mechanical Behavior of Grain Boundaries

2011 ◽  
Vol 1297 ◽  
Author(s):  
Chien-Kai Wang ◽  
Huck Beng Chew ◽  
Kyung-Suk Kim
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Virtual Work ◽  
Potential Interaction ◽  
Dislocation Nucleation ◽  
Nanometer Scale ◽  
Nonlinear Field ◽  
Boundary Slip ◽  
Nucleation Sites ◽  
Eam Potential

ABSTRACTA nonlinear field projection method has been developed to study nanometer scale mechanical properties of grain boundaries in nanocrystalline FCC metals. The nonlinear field projection is based on the principle of virtual work, for virtual variations of atomic positions in equilibrium through nonlocal interatomic interactions such as EAM potential interaction, to get field-projected subatomic-resolution traction distributions on various grain boundaries. The analyses show that the field projected traction produces periodic concentrated compression sites on the grain boundary, which act as crack trapping or dislocation nucleation sites. The field projection was also used to assess the nanometer scale failure processes of Cu Σ5 grain boundaries doped with Pb. It was revealed that the Pb dopants prevented the emission of dislocations by grain boundary slip and embrittles the grain boundary.

Atom-probe tomography of surface oxides and oxidized grain boundaries in alloys from nuclear reactors

2013 ◽  
Vol 1514 ◽  
pp. 107-118 ◽  
Author(s):  
Karen Kruska ◽  
David W Saxey ◽  
Takumi Terachi ◽  
Takuyo Yamada ◽  
Peter Chou ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Atom Probe Tomography ◽  
Nuclear Reactors ◽  
Bulk Material ◽  
Chemical Characterization ◽  
Atom Probe ◽  
Aqueous Environment ◽  
Pressurized Water ◽  
Surface Oxides

ABSTRACTThe preparation of site-specific atom-probe tomography (APT) samples containing localized features has become possible with the use of focused ion beams (FIBs). This technique was used to achieve the analysis of surface oxides and oxidized grain boundaries in this paper. Transmission electron microscopy (TEM), providing microstructural and chemical characterization of the same features, has also been used, revealing crucial additional information.The study of grain boundary oxidation in stainless steels and nickel-based alloys is required in order to understand the mechanisms controlling stress corrosion cracking in nuclear reactors. Samples oxidized under simulated pressurized water reactor primary water conditions were used, and FIB lift-out TEM and APT specimens containing the same oxidized grain boundary were prepared and fully characterized. The results from both techniques were found fully consistent and complementary.Chromium-rich spinel oxides grew at the surface and into the bulk material, along grain boundaries. Nickel was rejected from the oxides and accumulated ahead of the oxidation front. Lithium, which was present in small quantities in the aqueous environment during oxidation, was incorporated in the oxide. All phases were accurately quantified and the effect of different experimental parameters were analysed.

Grain Boundary Characteristics Evaluation by Atomistic Investigation Methods

2009 ◽  
Vol 1215 ◽  
Author(s):  
Yoshiyuki Kaji ◽  
Tomohito Tsuru ◽  
Yoji Shibutani
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Density Functional ◽  
Coincidence Site Lattice ◽  
Individual Characteristics ◽  
Material Strength ◽  
Investigation Methods ◽  
Grain Boundary Characteristics ◽  
The Individual ◽  
Boundary Characteristics

AbstractThe grain boundary has been recognized for one of the major defect structures in determining the material strength. It is increasingly important to understand the individual characteristics of various types of grain boundaries due to the recent advances in material miniaturization technique.In the present study three types of grain boundaries of coincidence site lattice (CSL), small angle (SA), and random types are considered as the representative example of grain boundaries. The grain boundary energies and atomic configurations of CSL are first evaluated by first-principle density functional theory (DFT) and the embedded atom method (EAM) calculations. SA and random grain boundaries are subsequently constructed by the same EAM and the fundamental characteristics are investigated by the discrete dislocation mechanics models and the Voronoi polyhedral computational geometric method. As the result, it is found that the local structures are well accorded with the previously reported high resolution-transmission electron microscope (HR-TEM) observations, and that stress distributions of CSL and SA grain boundaries are localized around the grain boundary core. The random grain boundary shows extremely heterogeneous core structures including a lot of pentagon-shaped Voronoi polyhedral resulting from the amorphous-like structure.

A Highly Reliable Al Line with Controlled Texture and Grain Boundaries

1995 ◽  
Vol 391 ◽  
Author(s):  
M. Hasunuma ◽  
H. Toyoda ◽  
T. Kawanoue ◽  
S. Ito ◽  
H. Kaneko ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Single Crystal ◽  
Grain Boundaries ◽  
Empirical Relation ◽  
Boundary Structure ◽  
Homogeneous Microstructure ◽  
Grain Boundary Structure ◽  
Dislocation Arrays ◽  
Order Of Magnitude ◽  
Individual Grains

AbstractIn order to clarify the relationship between Al line reliability and film microstructure, especially grain boundary structure and crystal texture, we have tested three kinds of highly textured Al lines, namely, single-crystal Al line, quasi-single-crystal Al line and hypertextured Al line, and two kinds of conventional Al lines deposited on TiN/Ti and on SiO2. Consequently, the empirical relation between the electromigration (EM) lifetime of Al line † and the (111) full width at half maximum (FWHM) value ω is described by † ∝ ω-2 [1]. This improvement of Al line reliability results from as following reasons; firstly, homogeneous microstructure and high activation energy of 1.28eV for the single-crystal Al line (ω=0.18°); secondly, sub-grain boundaries which consisted of dislocation arrays found in the quasi-single-crystal Al line (ω=0.26°) has turned out to be no more effective mass transport paths because dislocation lines are perpendicular to the direction of electron wind. Although there exist plural grain boundary diffusion paths in the newly developed hypertextured Al line (ω=0.5°) formed by using an amorphous Ta-Al underlayer {1], the vacancy flux along the line has been suppressed to the same order of magnitude of single crystal line. It has been clarified that the decrease of FWHM value has promoted the formation of sub-grain boundaries and low-angle boundaries with detailed orientation analysis of individual grains in the hypertextured film. The longer EM lifetime for the hypertextured Al line is considered to be due to the small grain boundary diffusivities for these stable grain boundaries, and this diffusivity reduction resulted in the suppression of void/hillock pair in the Al lines. These results have confirmed that controlling texture and/or grain boundary itself is a promising approach to develop reliable Al lines which withstand higher current densities required in future ULSIs.

Anisotropic Behaviour of Grain Boundaries

2005 ◽  
Vol 482 ◽  
pp. 63-70 ◽  
Author(s):  
Václav Paidar ◽  
Pavel Lejček
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Polycrystalline Materials ◽  
Grain Boundary Engineering ◽  
Interfacial Dislocation ◽  
Special Character ◽  
Boundary Properties ◽  
Properties Of Materials ◽  
Boundary Classification ◽  
Boundary Chemistry

Grain boundaries are decisive for many properties of materials. Due to short-range stress field their influence is primarily based on their atomic structure. Special character of grain boundary properties related to their structure, follows from the nature of atomic arrangements in the boundary cores, from the interfacial dislocation content and from the boundary mobility. All those aspects of boundary behaviour are strongly influenced by the boundary chemistry including various segregation phenomena. Approaches to the boundary classification and the interpretation of recent experimental results are discussed in the context of the complex relationship between microstructure and material properties. Such findings are essential for Grain Boundary Engineering proposed to improve the performance of polycrystalline materials.

Modeling Grain Boundary Damage Evolution in As-Measured 3D Microstructure

2011 ◽  
Author(s):  
I. Simonovski ◽  
L. Cizelj
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Early Development ◽  
Computational Models ◽  
Complex Geometry ◽  
Steel Wire ◽  
Constitutive Models ◽  
Element Model ◽  
Isotropic Elasticity ◽  
Individual Grains

In recent years we have seen a development of novel experimental techniques that enable one to non-destructively characterize polycrystalline microstructures. These techniques hold significant advantages over approaches like serial sectioning since the specimen is not destroyed in the characterization process. This is of immense value in advancing our understanding of materials and multiscale computational models. In particular, processes at the small length scales like the initiation and early development of grain boundary damage can now be measured more closely while the resulting simulations can now be directly compared to the experimental data. The task is, however, far from being simple as extremely complex geometry needs to be coupled with advance constitutive models for the bulk grain material and the grain boundaries themselves need to be combined. In this work a model, based on a X-ray diffraction contrast tomography data of a stainless steel wire with a diameter of 0.4 mm is presented. 3D topology and crystallographic orientation of individual grains are directly transferred into a finite element model. Grain boundary damage initialization and early development is then explored for a number of cases, ranging from isotropic elasticity up to crystal plasticity constitutive laws for the bulk grain material. In all cases the grain boundaries are modeled using the cohesive zone approach. Also, the stability of the simulations and measures aimed at improving it are reported upon.

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