Boundary Plane Distributions Research Articles

Influence of grain boundary plane distribution on ionic conductivity in yttria-stabilized zirconia sintered at elevated temperatures

The paper investigates electrical properties of fully stabilized zirconia, which is widely applied as a solid electrolyte in electrochemical devices such as solid oxide fuel cells. High ionic conductivity of these materials is crucial for effective operating of the devices; however, grain boundary resistivity limits conductivity in polycrystalline ceramics. Thus, optimisation of the microstructure of zirconia is necessary from an application point of view. Based on three-dimensional electron backscatter diffraction (3D EBSD) data, the research employed a complex impedance spectroscopy to establish a correlation between microstructure of cubic zirconia sinters and their conductivity. Samples with different levels of anisotropy in grain boundary plane parameters were investigated. The obtained results indicate that the conduction of ions through the grain boundaries is higher in the sample with the higher representation of the near-(001) grain boundaries. Such a relationship suggests that an over-representation of low-energy grain boundaries in zirconia polycrystals leads to an increase of ionic conductivity.

Effect of faceting on olivine wetting properties

Abstract Grain-scale pore geometry primarily controls the fluid distribution in rocks, affecting material transport and geophysical response. The dihedral angle (θ) in the olivine-fluid system is a key parameter determining pore fluid geometry in mantle wedges. In the system, curved and faceted olivine-fluid interfaces define θ, resulting in faceted-faceted (FF), faceted-curved (FC), and curved-curved (CC) angles. The effect of faceting on θ under various pressure and temperature (P-T) conditions and fluid compositions, however, has not been constrained, and mineralogical understanding remains unresolved. This study evaluated facet-bearing θ and their proportions in olivine-multicomponent aqueous fluid systems. Our results show that 1/3 of olivine-fluid θ are facet-bearing angles, regardless of the P-T conditions and fluid composition. Faceting produces larger dihedral angles than CC angles. The grain boundary plane (GBP) distribution reveals that the GBPs of faceted interfaces at triple junctions have low Miller index faces ({100}, {010}, and {101}). The misorientation angle/axis distributions of adjacent grain pairs are in accord with a theoretical distribution of random olivine aggregate. Moreover, the calculation of the FF angles for adjacent grain pairs with low Miller index GBPs reproduces measured angle values based on the olivine crystal habit. Therefore, our study suggests that the FF angle is strongly affected by olivine crystallography. The presence of faceting increases θ and a critical fluid fraction (φc) for percolation, lowering permeability. In the mantle wedge, where olivine crystallographic preferred orientation (CPO) is expected owing to corner flow, increasing the FF angle proportion with associated changes in fluid pore morphology will lead to permeability anisotropy, and controlling the direction of the fluid flow, and it will result in geophysical anomalies such as seismic wave attenuation and high electrical conductivity.

Study on deviation distribution of Σ3 and Σ9 boundaries in Hastelloy C-276 superalloy with different hot rolling reductions

In this study, the deviation distributions of Σ3 and Σ9 grain boundaries in a Hastelloy C-276 sheet were measured using electron backscatter diffraction technology (EBSD) and the grain boundary plane orientation was analyzed using a five-parameter technique after hot rolling at 900 °C with different thickness reductions. The results show that the relative areas of Σ3 grain boundary planes reveal a strong peak at the (111) twist position, and the corresponding intensity significantly decreases as the reduction increases. The hot rolling generates dislocations, resulting in significant deviation of Σ3 grain boundary orientations and the loss of special properties. However, the Σ9 grain boundary plane distribution (GBPD) becomes more diffused with increasing deformation, and the multiples of random distribution (MRD) value is ∼2. In addition, the large deviation of the Σ9 grain boundary orientation varies across the different strain samples. In low-strain samples, the deviation of the Σ9 grain boundary orientation may be affected by the Σ3 grain boundary deviation with construction of the Σ3–Σ3–Σ9 triple junction. The deformation microstructures mainly determine the deviation of the Σ9 grain boundary orientation in high-strain samples. Moreover, the distorted grain boundaries act as potent nucleation sites of dynamic recrystallization (DRX) during the hot rolling process.

The influence of γ-fibre texture on the grain boundary character distribution of an IF-steel

The current study revealed that the development of γ-fibre texture in IF-steel through static recrystallisation alters the distribution of grain boundary misorientations and plane orientations. In the initial transformed condition, the grain boundary plane distribution has a maximum at the (110) orientation. However, as the intensity of the γ-fibre texture increased, the maximum shifted to (111) and intensified. Furthermore, the presence of γ-fibre texture gradually increased the low angle boundary population at the expense of high angle boundaries, leading to a nearly uniform misorientation angle distribution. A calculation of the disorientation distribution assuming random orientations along the γ-fibre showed a flat distribution in the domain from 0 to 60°, consistent with the observations. The presence of γ-fibre texture changed the intensity, but not the shape of the grain boundary distribution at ∑3 = 60°/[111], which displayed maxima at low energy {112} symmetric tilt boundaries.

3D characterization of a nanostructured Al-Cu-Mg alloy

Three-dimensional (3D) characterization of variations in crystallography and chemistry of nanostructured metals will provide vital information to understand their mechanical and thermal behaviours. This study applied a surface sliding friction treatment (SSFT) at liquid nitrogen temperature to produce nanostructured surface layers in a peak-aged Al-Cu-Mg alloy. The nanostructured surface was characterized by means of 3D orientation mapping in the transmission electron microscope (3D-OMiTEM) and atom probe tomography (APT). 3D-OMiTEM results revealed a lamellar structure with an average lamellar boundary spacing of 26 nm at the topmost surface layer (depth < 20 μm), which is much finer than normally achievable in commercial purity Al deformed to high strain levels. Based on the 3D-OMiTEM data, a five-parameter grain boundary character analysis was carried out. It was found that low angle grain boundaries dominate the nanoscale structure and that the grain boundary plane distribution of high angle lamellar grain boundaries shows a preference around {101}. APT analysis showed segregation of Cu and Mg atoms at lamellar boundaries, which is believed to play a role in stabilizing the boundaries and enhancing the structural refinement during SSFT.

Five-parameter grain boundary character distribution of gold nanoparticles based on three dimensional orientation mapping in the TEM

Three-dimensional orientation mapping in the transmission electron microscope (3D-OMiTEM) has been used to characterize the grain structure of an ion-sputtered gold nanoparticle film. The three-dimensional morphology and crystallographic orientations of ∼7500 grains in more than 1200 nanoparticles were reconstructed. It was found that the grains have an average size of 8 nm and a weak crystallographic texture. A five-parameter grain boundary character analysis revealed that the microstructure mainly consists of Σ3, Σ9, Σ11, and Σ27a boundaries. Differences in the grain boundary plane distributions for these specific misorientations compared to those found for coarse grain-size materials were attributed to extensive grain boundary termination at nanoparticle surfaces. The grain boundary population is, nevertheless, on average inversely correlated to the grain boundary energy, as reported in previous studies. These findings can serve as a guide for tailoring the grain boundary character distribution and properties of nanoparticles and nanocrystalline thin films.

Microstructure evolution of 316L stainless steel during solid-state additive friction stir deposition

ABSTRACT Solid-state additive friction stir deposition was employed to three dimensionally print a 316L stainless steel. The microstructure, texture and grain boundary distribution were characterised using five-parameter boundary analysis. The bulk microstructure was exceptionally fine (∼0.7 µm) throughout the thickness of the deposited layers, consisting of equiaxed grains along with sub-grains delineated by high and low angle boundary segments. The misorientation angle distribution of the deposited layers was considerably different from the as-received microstructure, exhibiting a significant reduction in the relative areas of ∑3 annealing twin boundaries due to their distortion by severe plastic deformation. The overall texture also exhibited strong shear components associated with FCC metals, suggesting that the microstructure refinement largely took place through progressive subgrain rotation, known as continuous dynamic recrystallisation. The grain boundary plane distribution revealed significantly lower anisotropy compared with the as-received material, showing two moderate peaks at the (111) and (110) orientations. The migration of high-angle mobile boundaries, which may have been induced by thermal cycle upon subsequent deposition along with the dislocation gradients between adjacent grains, slightly enhanced the intensity of low energy (111) orientations at the expense of (110) high-energy boundaries.

Effect of manganese on the grain boundary network of lath martensite in precipitation hardenable stainless steels

The fully martensitic microstructures of a manganese bearing precipitation hardenable (PH) stainless steel and a commercial 17-4 PH steel were compared to investigate the influence of chemical composition on the grain boundary network of the lath martensitic microstructure. The martensitic transformation in both steels led to the bimodal misorientation angle distribution having multiple maxima at misorientations in the range of 10–15° and 50–60°. This closely matched with the misorientations between variants associated with the Kurdjumov-Sachs orientation relationship (K-S OR). However, the Mn addition appeared to relatively reduce the area of boundaries with misorientations near 60°. This was a result of the reduction in the area of 60°/[011] intervariant boundaries in the Mn bearing steel. The phenomenological theory of martensite revealed that the Mn addition altered the 3-variant clustering (i.e., V1V3V5) in 17-4PH steel to the 4-varaint clustering (i.e., V1V2V3V5) arrangement to minimize the strain associated with the displacive martensitic transformation, promoting the population of 60°/[111] intervariant boundaries at the expense of 60°/[011] intervariant boundary. The changes in local variant selection affected the connectivity of the grain boundary network, suggesting that grain boundary network characteristics (i.e., population and connectivity) of the lath martensite microstructure can be manipulated by altering the chemical composition of the steel. The five-parameter grain boundary analysis for both martensitic steels, however, revealed similar grain boundary plane distributions for all boundaries associated with the K-S OR, being terminated on {011} planes due to the constraint that results from the displacive phase transformation.

Orientation relationship of texture development in hot-rolled W during annealing

Severe through-thickness texture inhomogeneity is apt to occur during hot-rolling of tungsten. This raises the intriguing notion of how is the inhomogeneity affected by stress-involved or heat-involved factors of the thermo-mechanical process. The texture development in the bulk and at the surface were investigated, and the main focus was on the role of grain boundaries on texture development. The deformed texture at the surface and in the bulk seems similar, but the recrystallized texture of them evolves in entirely different manner, hence, the through-thickness effect is considered to be unilaterally triggered by heat-involved factor, i.e., “annealing” rather than “straining”. In the bulk, the recrystallized orientation basically retains the starting deformed γ-texture and θ-texture even if grain growth occurs. Meanwhile some subtle alternations (nucleation behaviors) show statistically a strong correlation with CSL relationships. At the surface, the deformed γ-texture is completely replaced by a prominent Goss texture ({110}〈001〉) at 1100 °C. The grain boundary plane distribution (GBPD) analysis demonstrates that the formation of Goss texture at the surface is controlled by low angle grain boundaries (LAGBs) and {112}〈111〉 or {100}〈110〉 oriented nucleation is controlled by Σ3 CSL boundary.

3D grain structure of an extruded 6061 Al alloy by lab-scale X-ray diffraction contrast tomography (DCT)

In this work, lab-scale X-ray diffraction contrast tomography (DCT) was conducted to investigate the 3D grain structure of α-Al in an extruded 6061 Al alloy. The morphological statistics of α-Al grains and the crystallographic characteristics including grain orientation, misorientation, and grain boundary plane orientation were analyzed. Grain boundary plane distributions of all grain boundaries or grain boundaries with specific misorientations were also revealed. A thorough understanding of the crystallographic characteristics of 6061 Al alloy is key to unlocking a more robust understanding of material performance.

Five-parameter characterization of intervariant boundaries in additively manufactured Ti-6Al-4V

Additive manufacturing has emerged as a promising route to fabricate complex-shaped Ti-6Al-4V parts. The microstructural evolution and variant selection across builds in response to different printing strategies processed by electron beam powder bed fusion has been previously clarified. However, a detailed knowledge of the grain boundary plane characteristics of the α-α intervariant interfaces is still missing. The aim of this study was to reveal the full ‘five-parameter’ crystallographic characteristics of the intervariant boundaries. The most common α-α intervariant for colony and basketweave microstructures was 60°/[1 1 2¯ 0], while in the acicular microstructure, the maximum was at 63.26°/[10¯ 5 5 3¯]. This is discussed in terms of self-accommodation during the β to α phase transformation, and the degree of coherence of the α laths in the as-deposited condition and during further growth. The grain boundary plane distributions reveal a high tendency for intervariant boundaries to terminate on prismatic and pyramidal planes rather than on low-energy basal planes. This suggests that, during additive manufacturing of Ti-6Al-4V and irrespective of the α morphology, the crystallographic constraints imposed by the Burgers orientation relationship determine the boundary plane distribution characteristics.

Recent Advances in EBSD Characterization of Metals

Electron backscatter diffraction (EBSD) has been attracting enormous interest in the microstructural characterization of metals in recent years. This characterization technique has several advantages over conventional ones, since it allows obtaining a wide range of characterization possibilities in a single method, which is not possible in others. The grain size, crystallographic orientation, texture, and grain boundary character distribution can be obtained by EBSD analysis. Despite the limited resolution of this technique (20–50 nm), EBSD is powerful, even for nanostructured materials. Through this technique, the microstructure can be characterized at different scales and levels with a high number of microstructural characteristics. It is known that the mechanical properties are strongly related to several microstructural aspects such as the size, shape, and distribution of grains, the presence of texture, grain boundaries character, and also the grain boundary plane distribution. In this context, this work aims to describe and discuss the possibilities of microstructural characterization, recent advances, the challenges in sample preparation, and the application of the EBSD in the characterization of metals.

Role of inclination dependence of grain boundary energy on the microstructure evolution during grain growth

The role of inclination dependence of grain boundary energy on the microstructure evolution and the orientation distribution of grain boundary planes during grain growth in polycrystalline materials is investigated by three-dimensional phase-field simulations. The anisotropic grain boundary energy model uses the description of the faceted surface structure of the individual crystals and constructs an anisotropic energy of solid-solid interface. The energy minimization occurs by the faceting of the grain boundary due to inclination dependence of the grain boundary energy. The simulation results for a single grain show the development of equilibrium shapes (faceted grain morphologies) with different families of facets which agrees well with the theoretical predictions. The results of grain growth simulations with isotropic and anisotropic grain boundary energy for cubic symmetry show that inclination dependence of grain boundary energy has a significant influence on the grain boundary migration, grain growth kinetics and the grain boundary plane distribution. It has been shown that the model essentially reproduces the experimental studies reported for NaCl and MgO polycrystalline systems where the anisotropic distribution of grain boundary planes has a peak for the low-index {100} type boundaries.

Nondestructive evaluation of 3D microstructure evolution in strontium titanate

Nondestructive X-ray diffraction contrast tomography imaging was used to characterize the microstructure evolution in a polycrystalline bulk strontium titanate specimen. Simultaneous acquisition of diffraction and absorption information allows for the reconstruction of shape and orientation of more than 800 grains in the specimen as well as porosity. Three-dimensional microstructure reconstructions of two coarsening states of the same specimen are presented alongside a detailed exploration of the crystallographic, topological and morphological characteristics of the evolving microstructure. The overall analysis of the 3D structure shows a clear signature of the grain boundary anisotropy, which can be correlated to surface energy anisotropy: the grain boundary plane distribution function shows an excess of 〈100〉-oriented interfaces with respect to a random structure. The results are discussed in the context of interface property anisotropy effects.

Five-parameter grain boundary characterisation of randomly textured AZ31 Mg alloy

ABSTRACTThe five-parameter analysis approach was used to measure the grain boundary character distribution of randomly textured AZ31 Mg alloy produced through casting followed by annealing at 450°C for 16 h. The misorientation angle distribution was close to the one expected from the material with a random texture. The grain boundary plane distribution, ignoring the misorientation angle, revealed a relatively weak plane orientation anisotropy, with a preference for grain boundaries terminated on prismatic planes. Surprisingly, the population of grain boundary planes was not inversely related to the expected grain boundary energies. Basal oriented grain boundaries are expected to have the lowest energy, but they also had the lowest population. This could result from the presence of residual columnar grains, formed during solidification and remaining after annealing, which increases the relative area of boundary planes with prismatic orientations.

The grain boundary character distribution in thermomechanically processed rare earth bearing magnesium alloy

The present work was conducted to examine the grain boundary character distribution in a rare earth elements bearing magnesium alloy during thermomechanical processing (TMP). To this end, the friction stir processing was applied as an effective TMP scheme through single and completely overlaid three-pass trials. The results indicated that along with the progressive substructure development and significant grain refinement, the fractions of coincidence site lattice boundaries were also increased in processed materials. The twin based special boundaries (holding 15b character) and the perfect coincidence ones (holding 13a character) were found as the most common coincidence site lattice boundaries. These were directly resulted from the occurrence of twinning induced dynamic recrystallization and progressive lattice rotation, respectively. The higher strain accumulation at the twin based boundary indicated the higher instability of them in comparison to the perfect coincidence one. The deformed microstructures were also consisted of a new specific kind of high angle grain boundary holding the rotating axis of <15-6-95>. The tilt nature of the boundary plane distribution was well approved the relatively stable character of this new type of special boundary. The micro-textures of the processed materials were also examined and the preferred orientation of developed special boundaries were characterized.

Grain boundary crystallography in polycrystalline yttria-stabilised cubic zirconia

Properties of grain boundaries such as grain boundary energy, mobility and diffusion are reported to depend strongly on their crystallography. While studies on ceramic bicrystals with low Σ misorientations have shown highly ordered structures and low energies, studies on dense polycrystalline ceramics often show the significance of grain boundary planes. In the present study, grain boundary plane distributions were studied for yttria-stabilised cubic zirconia with varying grain sizes using Electron Back Scattered Diffraction technique combined with a stereological approach. Despite nearly isotropic grain boundary plane distributions, a highly anisotropic grain boundary character distribution is observed for specific misorientations. Certain low-energy symmetric tilts such as Σ3 and Σ11 are found to occur with high frequencies across the grain size range studied, leading to an inverse correlation between GB energy and frequency of occurrence, consistent with other ceramics studied in literature.

Grain boundary plane distribution and its potential correlation with magnetic properties in hexagonal RCo5 permanent magnets.

Grain boundary plane distributions (GBPDs) are demonstrated to be spatially inhomogeneous in RCo5 permanent magnets. The potential effect of GBPDs on magnetic properties is proposed from major performance considerations, and approaches to exactly differentiate the boundary population are introduced. The crystallographic texture in permanent magnets should cover not only the texture of the crystals, but also the texture between crystals, which is helpful to advance the present understanding of the relationship between textures and properties in permanent magnets.

Effect of ferrite-to-austenite phase transformation path on the interface crystallographic character distributions in a duplex stainless steel

The effect of the ferrite to austenite phase transformation route on the microstructure and interface plane character distributions was studied in a duplex stainless steel. Two markedly different austenite morphologies (i.e., equiaxed and Widmanstätten) were produced through diffusional (slow cooling) and semi-shear (air-cooling) transformations, respectively. Both austenite morphologies had textures similar to the as-received condition, which was attributed to a “texture memory” effect. The air-cooled microstructure displayed a significantly higher content of Kurdjumov-Sachs (K-S) and Nishiyama-Wassermann (N-W) interfaces (39%) compared with the slow-cooled one (16%), due to the change in the austenite nucleation and growth mechanism during the phase transformation. A five-parameter analysis of different interfaces revealed that for K-S/N-W orientation relationships, ferrite and austenite terminated on (110) and (111) planes, respectively, regardless of the transformation route. The population of these planes, however, increased as the transformation rate increased. A higher fraction of Σ3 boundaries was observed in the equiaxed austenite morphology compared with its Widmanstätten counterpart, which was mainly attributed to the different kinetics and the growth mode of austenite plates during the phase transformation. Σ9 boundaries were mostly formed where two Σ3 boundaries met and were largely of tilt character because of geometric constraints. The intervariant boundary plane distributions of both austenite microstructures displayed more frequent {111} orientations than other planes for a majority of the boundaries. This trend was markedly stronger for Widmanstätten austenite.

Evaluation of grain boundary plane distribution in yttria stabilized polycrystalline zirconia based on 3D EBSD analysis

In this work we have investigated grain boundary plane distributions in the yttria stabilized zirconia samples sintered at 1450, 1500, and 1550°C for 2h. Since all our samples were sintered in different thermal conditions, they also differ significantly as far as microstructure is concerned. Average grain sizes vary from 2.22±0.08μm to 4.11±0.18μm depending on the sintering temperature. The question whether these differences have an impact on the GBP distributions needs to be answered. In the stabilized zirconia samples sintered at the temperature of 1450°C and 1500°C boundaries having (001) planes in one of the grains were over-represented. The evidence for over-representation of such boundaries in the zirconia ceramics sintered at 1550°C is apparently too weak. The frequencies of occurrence of twist, symmetric, and 180°-tilt boundaries in zirconia were estimated for ceramic material for the first time. It must be underlined that all distributions presented in this paper were obtained directly from the 3D EBSD measurements.