Overview no. 61 On geometric criteria for low interfacial energy

Sutton, A. P.; Balluffi, R. W.

doi:10.1016/0001-6160(87)90067-8

Cited by 371 publications

(115 citation statements)

References 37 publications

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“…Although strong gradients in γ have been measured near misorientation values of special coincident site lattice (CSL) boundaries and twin boundaries, the shape (depth and width) of these so-called "energy cusps" is not well understood and may disappear at elevated temperatures (42,44). In addition, aluminum is known to have a high stacking fault energy, which limits twinning (45).…”

Section: Discussionmentioning

confidence: 99%

Direct observation of grain rotations during coarsening of a semisolid Al–Cu alloy

Dake

Oddershede

Sørensen

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Sintering is a key technology for processing ceramic and metallic powders into solid objects of complex geometry, particularly in the burgeoning field of energy storage materials. The modeling of sintering processes, however, has not kept pace with applications. Conventional models, which assume ideal arrangements of constituent powders while ignoring their underlying crystallinity, achieve at best a qualitative description of the rearrangement, densification, and coarsening of powder compacts during thermal processing. Treating a semisolid Al-Cu alloy as a model system for late-stage sintering-during which densification plays a subordinate role to coarsening-we have used 3D X-ray diffraction microscopy to track the changes in sample microstructure induced by annealing. The results establish the occurrence of significant particle rotations, driven in part by the dependence of boundary energy on crystallographic misorientation. Evidently, a comprehensive model for sintering must incorporate crystallographic parameters into the thermodynamic driving forces governing microstructural evolution.3D microstructural evolution | sintering | Ostwald ripening | grain rotation | x-ray imaging W hether we realize it or not, our daily lives are marked by encounters with sintering, ranging from natural rock formations and glaciers to artificial products like the porcelain from which we eat or the amalgam fillings in many teeth. Sintering is an efficient method for combining loose granular precursors into solid objects of predetermined shape at relatively low temperature, circumventing the processing route of melting, casting, and machining. The applications of sintering are widespread. For example, it is the predominant method for producing bulk technical ceramics (1), and, thanks to advances in powder metallurgy, sintering is of growing importance in the fabrication of metals, as well (2). The focus in recent years on nanostructured materials-specifically, on materials for energy storage and conversion-has intensified the scientific investigation and modeling of sintering processes. The latter find application in the production of fuel cells (3) and battery electrodes (4). In other applications, such as catalysis (5), sintering can be highly undesirable, as it reduces the connectivity of pores and the free surface of nanoparticles. In all of these cases, we need a firm understanding of sintering fundamentals to achieve and retain desired materials properties during thermal processing.The reduction in free energy that accompanies the removal of a powder compact's surface area is the driving force behind sintering (2, 6). When two particles come into contact, two free surfaces are replaced by a single solid/solid boundary. If the particles are crystalline, the new interface is a grain boundary, the (excess) energy of which is generally on the order of one-third of that of a (single) free surface of equal area (6); consequently, the sintering process results in a net release of energy. As free surface area decreases, the powder ...

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Section: Discussionmentioning

confidence: 99%

Direct observation of grain rotations during coarsening of a semisolid Al–Cu alloy

Dake

Oddershede

Sørensen

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…We begin by noting that high angle boundaries can be distinguished in alloys by the degree of solute enrichment, Hondros et al 18) Two broad categories have been found, i.e., general high angle boundaries with relatively high values of enrichment, and a few special grain boundaries distinguished by low enrichment. To characterize special grain boundaries, various bulk geometrical parameters are used, the most widely being the coincidence site lattice (CSL) description, S. It must be noted that Sutton and Balluffi 19) in their overview could find no correlation between a geometrical description, such as S, with low grain boundary energy. Nonetheless, this description continues to be used in discussions of the origins of the Goss texture, even though these geometrical parameters can, at best, be only rough estimates of the locations of energy minima, Hondros et al, 18) see also Morawiec.…”

Section: Discussionmentioning

confidence: 99%

Formation of the Goss Texture in a Thin Foil Experiment on Fe–3.2%Si

2010

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shows the same areas, only this time the Goss orientations are shaded. The Goss grains are located in the h fibre distribution and in this the Goss grains are concentrated. It is plain from Figs. 2 and 3 that the h fibre is more intense in some regions than in others, i.e., it occurs in patches across the sheet plane and it is most concentrated in the sub-surface quarter thickness layers. Figure 4 shows the effects of heating at 970°C in a salt bath for 1, 5 and 10 min. Secondary recrystallization has begun in the top surface after 1 min, Fig. 4(a), and that it originates at both surfaces is the most probable explanation for the centre-line effect after 5 min annealing, Fig. 4(b). After 10 min secondary grains have grown to impinge both surfaces, and the process is now almost complete, Fig. 4(c). The orientation of the obvious secondary grains are widely scattered around the Goss orientation after 1 min, and the texture quite obviously becomes much more closely aligned with Goss as time at 970°C continues, ISIJ International, Vol. 50 (2010) TD cross sections covering the whole sheet thickness of a primary recrystallized sample. The orientations outlined by gray and dark lines correspond to ( Fig. 2(a and b)) the central thickness g fibre grains and subsurface h fibre (Fig. 2(c and d)) grains, respectively., Fig. 4(f). This texture sharpening is also well-known. In order to check the effects of the as-processed surface on subsequent secondary recrystallization, about 20-25 mm of material was removed from both sides before annealing. This is indicated schematically in Fig. 5(a), and the texture results after complete secondary recrystallization i.e., when secondaries were of sheet thickness, are shown in Fig. 5(b). Comparing Figs. 4(f) with 5(b) shows that any effects associated with the surfaces are not significant.A sub-surface foil of 80 mm in thickness was carefully electropolished from the as-received sheet, and another foil of this thickness was prepared from the centre of the sheet. The geometry is shown in Fig. 6(a). It was found that secondary recrystallization occurred rapidly in both foils, but growth stagnated after 570 min at 1 000°C in the vacuum furnace. In the sub-surface foil grains ranged in size from 100 to 1 300 mm, while in the central foil the range was smaller, i.e., from 100 to 900 mm. In all cases the largest grains occupied the whole thickness of the foils. Fig. 6(b) shows a {100} pole figure of all the grains of size greater than 100 mm, and Fig. 6(c) those larger than 600 mm found in the sub-surface foil. It is plain that the largest grains shown in Fig. 6(b) contain a subset clustered around the Goss orientation, Fig. 6(c). When the data from the central foil is similarly processed, the texture is mostly {111}͗hkl͘ Fig. 6(d), as is the subset from the largest grains, Fig. 6(e). This set of results indicate that Goss oriented grains, which exist throughout the thickness of the sheet, Fig. 3, grow preferentially in the subsurface h fibre layer Fig. 2. That it can and does grow prefe...

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“…Specifically, the cells of rectangle shape (NB: the hexagonal shape can be transformed into rectangle shape) could always be matched easily after some unit repeating operations, which is in pursuit of existence of a coincidence site lattices 43,44 (CSL). Comparatively, the cells of parallelogram with unequal neighboring sides and a non-right angle are difficult to be matched with the others.…”

Section: The Matching Of Shape and Lattice Constants Of The Cellsmentioning

confidence: 99%

“…The first criterion is easily understandable. The second one is based on the observation 43,45 that the grain boundaries between two identical materials are often found to have a CSL with small unit cell volume. The information about the size of our repeated cells is specified in Table II. In summary, the rectangle cell (original or transformed) is always preferred in the process of choosing the surface of each phase.…”

Section: The Matching Of Shape and Lattice Constants Of The Cellsmentioning

confidence: 99%

Modeling and stabilities of Mg/MgH2 interfaces: A first-principles investigation

et al. 2014

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We have theoretically investigated the modeling and the structural stabilities of various Mg/MgH2 interfaces, i.e. Mg($10\bar 10$101¯0)/MgH2(210), Mg(0001)/MgH2(101) and Mg($10\bar 10$101¯0)/MgH2(101), and provided illuminating insights into Mg/MgH2 interface. Specifically, the main factors, which impact the interfacial energies, are fully considered, including surface energies of two phases, mutual lattice constants of interface model, and relative position of two phases. The surface energies of Mg and MgH2, on the one hand, are found to be greatly impacting the interfacial energies, reflected by the lowest interfacial energy of Mg(0001)/MgH2(101) which is comprised of two lowest energy surfaces. On the other hand, it is demonstrated that the mutual lattice constants and the relative position of two phases lead to variations of interfacial energies, thus influencing the interface stabilities dramatically. Moreover, the Mg-H bonding at interface is found to be the determinant of Mg/MgH2 interface stability. Lastly, interfacial and strain effects on defect formations are also studied, both of which are highly facilitating the defect formations. Our results provide a detailed insight into Mg/MgH2 interface structures and the corresponding stabilities.

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Overview no. 61 On geometric criteria for low interfacial energy

Cited by 371 publications

References 37 publications

Direct observation of grain rotations during coarsening of a semisolid Al–Cu alloy

Direct observation of grain rotations during coarsening of a semisolid Al–Cu alloy

Formation of the Goss Texture in a Thin Foil Experiment on Fe–3.2%Si

Modeling and stabilities of Mg/MgH2 interfaces: A first-principles investigation

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