Grain Boundary Plane Orientation Research Articles

Grain-boundary plane orientation dependence of faceting–roughening transition in Au grain boundaries under electron-beam irradiation

Grain boundaries act to absorb and annihilate point defects generated by high-energy particles for polycrystalline nuclear materials. Thus, understanding the effect of irradiation of high-energy particles on the grain-boundary structural change is prerequisite to develop nuclear materials with desirable properties. It is expected that such an effect would be different for different GB characters. To explore the probability, we examine grain boundaries with twist and tilt components with the same misorientation relationship of [1 0 0]/45o in Au as a model system at a high-voltage transmission electron microscope with an acceleration voltage of 1250 keV. It is observed that, under the same irradiation condition, the tilt GB undergoes roughening while the twist one became faceted.

Preferred orientation of grain boundary plane in recrystallized high purity aluminum

Compared with the research of preferred orientation of crystals (crystallographic texture) which started nearly a century ago, preferred orientation of grain boundary plane in polycrystalline materials is a lately proposed research direction with the development of five parameter analysis which is based on electron backscatter diffraction and stereological method. Systematic investigations into the preferred orientation of grain boundary plane and in-depth understanding on their evolution natures will be important to the manipulation of the microstructures of desired properties. In current paper, high purity aluminum (99.99 wt%) samples were cold rolled with 85% thickness reduction followed by a recrystallization annealing at 330℃ for 15-60 minutes and then the grain boundary plane orientations were studied. The results indicate there indeed exist preferred orientations of grain boundary planes in the recrystallized microstructure and the preferred orientation evolves sequentially from {2 2 3} to {1 1 1} and {1 0 0} planes during grain growth. Further discussion points out the recrystallization of high purity aluminum after cold rolling could be a so-called continuous recrystallization which involves sub-grain coalescence and sub-grain growing, and low angle grain boundary (mis- orientation angles ranging from 2° to 15°) constitutes the main part of the entire grain boundaries in the recrystallized microstructure. During grain growth, the crystallographic texture evolves from {1 1 0}<1 1 2> (Brass) to {0 1 1}<1 0 0> (Goss) and {0 2 3}<1 0 0>co- existed, and low angle grain boundary planes usually orient on the exact position of low energy tilt boundaries due to the effects of crystallographic texture and crystallographic plane energy. This is the reason for the regular evolution of the preferred orientation of grain boundary planes as observed.

Effect of plastic deformation on the Σ2 grain boundary plane distribution in WC–Co cemented carbides

Grain boundary plane distributions have been measured for Σ2 grain boundaries (boundaries that have a 90degree rotation about the [10-10] axis) in undeformed and plastically deformed WC–Co cemented carbides. By virtue of electron backscattered diffraction data coupled with the five parameter analysis method, the measurements show that while the misorientations of the Σ2 boundaries are 20% reduced by the plastic deformation, there are 33% reduction in the orientation of the Σ2 twist grain boundary plane. A dislocation model for grain boundary plane reorientation during plastic deformation is proposed.

Grain Boundary Plane Distributions in a Hot Rolled 5A06 Aluminum Alloy

To investigate the preferential distribution of grain boundary planes in a hot rolled aluminum alloy, the electron backscattered diffraction approach and five‐parameter analysis method are used to characterize the grain boundary plane distributions in a hot rolled 5A06 aluminum alloy, and the results show that the orientations of grain boundary planes are textured. Grain boundary planes favor the {111} orientation at the center of the specimen, and their population is 56% higher than that in a random distribution, whereas grain boundary planes favor the {110} orientation on the surface of the specimen, and their population is 69% higher than that in a random distribution. Moreover, this anisotropic distribution of grain boundary planes occurs at all misorientation angles. The study suggests a new understanding of the pathway to evaluate the crystallographic orientation dependent performances.

Effect of grain boundary character on sink efficiency

The dependence of the width of void-denuded zones (VDZs) on grain boundary (GB) characters was investigated in Cu irradiated with He ions at elevated temperature. Dislocation loops and voids formed near GBs during irradiation were characterized by transmission electron microscopy, and GB misorientations and normal planes were determined by electron back-scatter diffraction. The VDZ widths at Σ3〈110〉 tilt GBs ranged from 0 to 24nm and increased with the GB plane inclination angle. For non-Σ3 GBs, VDZ widths ranged from 40 to 70nm and generally increased with misorientation angle. Nevertheless, there is considerable scatter about this general trend, indicating that the remaining crystallographic parameters also play a role in determining the sink efficiencies of these GBs. In addition, the VDZ widths at two sides of a GB show different values for certain asymmetrical GBs. Voids were also observed within GB planes and their density and radius also appeared to depend on GB character. We conclude that GB sink efficiencies depend on the overall GB character, including both misorientation and GB plane orientation.

New method to characterise grain boundary plane orientations based on EBSD orientation microscopy for serial sectioned surfaces

A new 'elementary facet' method has been developed to measure grain boundary (GB) plane orientations using three-dimensional electron backscattered diffraction on serial sectioned surfaces in a sample. The method defines different types of elementary facets in an orthogonal coordinate system in the sample. These elementary facets are used to pave GBs. For a flat GB, its projected areas on the orthogonal coordinate planes in the sample are obtained from the numbers of different facets paved in the GB. From the projected areas of the GB plane in the three coordinate planes, the GB plane normal is derived. For uneven GBs, a convolution method has been developed to obtain the GB plane orientations at different GB locations. In essence, this new method measures the GB orientations at every elementary facet that is used to pave the GBs in the sample. Together with the measured crystal orientations of different grains, the GB five parameters at all facets can be obtained readily. The distribution of GB five parameters for the whole GB population in a sample can be derived from the collection of properties of individual GB facets in the sample.

On the atomic structure of an asymmetrical near Σ = 27 grain boundary in copper

The atomic structure of an asymmetrical near Σ = 27 {525} tilt grain boundary (GB) in copper is determined by coupling high-resolution transmission electron microscopy and molecular dynamics simulation. The average GB plane is parallel to {414} in crystal (1) and {343} in crystal (2). The detailed GB structure shows that it is composed of facets always parallel to {101} and {111} in crystals (1) and (2), respectively. The atomic structure of one facet is described using the structural units model. Each facet is displaced with respect to its neighbours by a pure step, giving rise to the asymmetry of the GB plane orientation. The energy of this asymmetrical GB is significantly lower than that of both the {525} symmetrical and the {11,1,11}/{111} asymmetrical Σ = 27 GBs. One GB region displays another atomic structure with a dislocation that accounts for the misfit between interatomic distances in the {414} and {343} GB planes.

Grain-boundary plane orientation dependence of electrical barriers at Σ5 boundaries in SrTiO 3

Dependence of the electrical properties on grain-boundary plane orientation is examined by a combination of high-resolution transmission electron microscopy, impedance spectroscopy, and electron energy-loss spectrometry using two kinds of SrTiO 3 Σ5 ([1 0 0]/36.8°) bicrystalline grain boundaries: symmetric (3 1 0) (18.4°/18.4°) and asymmetric (8.4°/28.4°). While the symmetric grain boundary is observed to be straight with the symmetric (3 1 0)//(3 1 0) plane orientation, the asymmetric grain boundary is faceted into symmetric (3 1 0)//(3 1 0) and (2 1 0)//(2 1 0), and asymmetric (1 0 0)//(4 3 0). Grain-boundary impedance is observed only in the asymmetric grain boundary, and the electron energy-loss spectrometry quantification indicates that the asymmetric (1 0 0)//(4 3 0) facets are more oxygen-deficient than the symmetric ones. The results suggest that the asymmetric (1 0 0)//(4 3 0) facets are the most resistive among the three different facets.

Bifurcation and Deviation of Cleavage Paths at Through-Thickness Grain Boundaries

The behavior of cleavage crack fronts at grain boundaries in free-standing silicon thin films is investigated through a microtensile experiment. In addition to the crystallographic orientation, the orientation of grain boundary plane also plays a critical role. With respect to the initial crack surface, if the inclination angle is relatively small, the crack tends to penetrate across the boundary; if the angle is large, the crack may either bifurcate along the boundary or turn back on another crystallographic plane. The former is triggered by crack front transmission, and the latter may result in a higher critical crack growth driving force.

Correlation Between Grain‐Boundary Segregation and Grain‐Boundary Plane Orientation in Nb‐Doped TiO2

Grain‐boundary (GB) segregation has been measured in Nb‐doped TiO2 (rutile) by Auger electron spectroscopy analyses of the two surfaces exposed by inter‐granular fracture. In addition, the orientations of the exposed GB planes on both sides of the fracture surface have been determined. A strong anisotropy of GB composition is found. Measurements on 166 individual GB fracture surfaces show that boundary planes with low and high levels of segregation tend to be clustered along the (110)–(010) and (001)–(011) regions of the stereographic triangle, respectively. The matching halves of GB planes with either high or low segregation also tend to be terminated by planes in the same respective regions of orientation space. High and low levels of segregation occur in regions of GB plane orientation space estimated to correspond to high and low GB energy, respectively. This trend is consistent with qualitative arguments based on Gibbsian adsorption.

Grain Growth in Al: First Results from a Combined Study of Bulk and In-Situ Experiments Using a Columnar Structured Al Foil

First results from grain growth experiments in a columnar structured Al foil show several interesting features: (a) the grain size distribution remains heterogeneous even after up to 300 min. annealing and (b) the Von Neumann-Mullins relation is not always satisfied. To clarify the underlying reasons for these features, in-situ heating experiments within a Scanning Electron Microscope (SEM) were combined with detailed Electron Backscatter Diffraction (EBSD) analysis. These show that the movement of boundaries can be strongly heterogeneous. For example, the complete replacement of one grain by a neighbouring grain without significant change of the surrounding grain boundary topology is frequently seen. Experiments show that grain boundary energy and/or mobility are anisotropic both with respect to misorientation and orientation of grain boundary plane. Low energy and/or mobility boundaries are commonly low angle boundaries, twin boundaries and boundaries that form traces to a low index plane of at least one of the adjacent grains. As a consequence the Von Neumann-Mullins relation is not always satisfied.

New stereology for the recovery of grain-boundary plane distributions in the crystal frame

A new experimental method is given for recovering the probability-distribution function S v ( $$\hat n_A $$ |Δg). The function S v ( $$\hat n_A $$ |Δg) is the grain-boundary area per unit volume as a function of grain-boundary plane orientation ( $$\hat n_A $$ ), given a lattice misorientation (Δg) between the adjoining grains. The grain-boundary normal ( $$\hat n_A $$ ) is expressed in the crystal frame in which the misorientation Δg originates. The proposed method recovers the three-dimensional S v ( $$\hat n_A $$ |Δg) function using data taken from two-dimensional section planes. The method requires the measurement of many grain-boundary trace (in-plane) angles and lengths associated with grain boundaries of lattice misorientation. All such boundary traces may be observed from a single section plane if the crystallographic texture is sufficiently random. In heavily textured microstructures, the method requires the researcher to observe traces from multiple oblique section planes cut through the material. A method of quantitatively estimating whether the texture is sufficiently random is given. Simulations on both textured and nontextured microstructures demonstrate the validity of the method. Experimentally, the new method is used to analyze boundaries of misorientation (Σ3) observed in 304 stainless steel. Calculated grain-boundary plane-probability functions are shown to be consistent with what is already known.

Distribution of grain boundaries in magnesia as a function of five macroscopic parameters

A semi-automated method has been used to measure all five macroscopically observable parameters of 4.1×10 6 boundary plane segments making up 5.4 mm 2 of boundary area in a hot-pressed magnesia polycrystal. The observations allow a complete description of the distribution of crystal orientations, grain boundary misorientations, and the crystallographic orientations of grain boundary planes. Among the low misorientation angle grain boundaries, there is a preference for tilt boundaries, especially those with boundary plane normals in the <110> direction. At all fixed misorientations, there is a preference for boundaries with a boundary plane normal in the <100> direction. These boundaries are generally asymmetric and occur at least twice as frequently as the average boundary for each fixed misorientation.

Structure and morphology of nanosized lead inclusions in aluminum grain boundaries

Grain boundary lead inclusions formed by ion implantation of mazed bicrystal aluminum films have been investigated by transmission electron microscopy. The vapor-grown bicrystal films contained mainly 90°(110) tilt boundaries with fixed misorientation but variable inclination, as well as some growth twins with 70.5°(110) symmetrical tilt boundaries and a few small-angle boundaries. It was found that the shape, size and orientation of the inclusions in the grain boundaries depend on the orientation of the aluminum grain boundary plane. Inclusions at 90°(110) tilt boundaries were invariably sharply faceted toward one aluminum grain and more rounded toward the other grain. The faceted side was a section of the cuboctahedral equilibrium shape of bulk lead inclusions in parallel topotaxy with the aluminum matrix. The rounded side, where the aluminum grain was rotated by 90° with respect to the lead lattice, approximated a spherical cap. At specific low-energy segments of the grain boundary where a (100) plane in grain 1 meets an (011) plane in grain 2, only two of several possible shapes were observed. One of these was preferred in as-implanted samples while both types were found after melting and re-solidification of the lend inclusions. The observations are discussed in terms of a modified Wulff construction.

The distribution of grain boundary plane orientations in a metastable grain aggregate

Etude dans un ecchantillon polycristallin d'acier inoxydable contenant des grains recristallises.Comparaison avec l'approche du reseau de site de coincidence.