The structure and properties of high‐angle grain boundaries in metals

Gleiter, H.

doi:10.1002/pssb.2220450102

Cited by 95 publications

(18 citation statements)

References 53 publications

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“…The temperature dependence of the grain boundary mobility is determined by performing a series of half-loop migration simulations at different temperatures for fixed half-loop width, w. According to Eqs. (2) and 3, the mobility should be proportional to (1/T ) exp(−Q/kT ). For (Q/kT ) 1, the (1/T ) dependence of the mobility will be negligible and the activation energy for grain boundary migration can be obtained from the slope of a plot of ln(M) versus (1/T ).…”

Section: Methodsmentioning

confidence: 99%

“…The atomic structure of grain boundaries determines the grain boundary thermodynamics and the mechanism of grain boundary migration. The structure of grain boundaries has been the subject of extensive research over the past quarter century (see [2][3][4] for a review). Driving forces for interface migration include interface curvature and differences in free energy of the phases, strain energy and/or defect densities across the interface.…”

Section: Introductionmentioning

confidence: 99%

“…A similar expression can be written for the case where the boundary moves by the collective motion of a group of atoms [21]. Equation (2) suggests that the velocity is directly proportional to the driving force. The proportionality constant is only a function of material properties, physical constants and temperature and is known as the grain boundary mobility, M:…”

Section: Introductionmentioning

confidence: 99%

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Untitled

1998

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We present two dimensional molecular dynamics simulations of grain boundary migration using the half-loop bicrystal geometry in the experiments of Shvindlerman et al. We examine the dependence of steady-state grain boundary migration rate on grain boundary curvature by varying the half-loop width at constant temperature. The results confirm the classical result derived by absolute reaction rate theory that grain boundary velocity is proportional to the curvature. We then measure the grain boundary migration rate for fixed half-loop width at varying temperatures. Analysis of this data establishes an Arrhenius relation between the grain boundary mobility and temperature, allowing us to extract the activation energy for grain boundary migration. Since grain boundaries have an excess volume, curvature driven grain boundary migration increases the density of the system during the simulations. In simulations performed at constant pressure, this leads to vacancy generation during the boundary migration, making the whole migration process jerky.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Untitled

1998

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“…Recent molecular dynamics (MD) simulations of polycrystalline metals, at high temperatures and under external stresses, have indeed provided substantial support for the glassy behavior of HAGBs (13,14). On the other hand, an amorphous HAGB would imply that its interfacial energy is insensitive to the grain misorientation angle (9,15,16). Nevertheless, GB mobility and diffusion, which have a strong dependence on the interfacial energy, are found to vary with the misorientation angle (17,18).…”

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confidence: 99%

Confined glassy dynamics at grain boundaries in colloidal crystals

Nagamanasa

Gokhale

Ganapathy

et al. 2011

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

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Grain boundary (GB) microstructure and dynamics dictate the macroscopic properties of polycrystalline materials. Although GBs have been investigated extensively in conventional materials, it is only recently that molecular dynamics simulations have shown that GBs exhibit features similar to those of glass-forming liquids. However, current simulation techniques to probe GBs are limited to temperatures and driving forces much higher than those typically encountered in atomic experiments. Further, the short spatial and temporal scales in atomic systems preclude direct experimental access to GB dynamics. Here, we have used confocal microscopy to investigate the dynamics of high misorientation angle GBs in a three-dimensional colloidal polycrystal, with single-particle resolution, in the zero-driving force limit. We show quantitatively that glassy behavior is inherent to GBs as exemplified by the slowing down of particle dynamics due to transient cages formed by their nearest neighbors, non-Gaussian probability distribution of particle displacements and string-like cooperative rearrangements of particles. Remarkably, geometric confinement of the GB region by adjacent crystallites decreases with the misorientation angle and results in an increase in the size of cooperatively rearranging regions and hence the fragility of the glassy GBs.colloids | polycrystals | glasses G rain boundaries (GBs)-thin interfaces that separate adjacent regions with different crystallographic orientation in polycrystals (1)-are central to our understanding of deformation and fracture mechanisms (2), melting kinetics (3), and transport properties (4) in a wide class of natural and man-made materials. An active area of materials research is to elucidate the spatiotemporal evolution of GBs and dynamics of their constituent atoms to better understand processes for enhancing material performance, which include Hall-Petch strengthening (5, 6) and GB engineering (7). Dislocation GBs resulting from small mismatches in grain orientation are reasonably well-understood (8). However, high misorientation angle grain boundaries (HAGBs), which play a crucial role in plastic deformation and grain growth, continue to pose a challenge (9). Observations of GB embrittlement at low temperatures (10) and with impurity doping (11, 12) have led to suggestions that HAGBs might share similarities with glass-forming liquids. Recent molecular dynamics (MD) simulations of polycrystalline metals, at high temperatures and under external stresses, have indeed provided substantial support for the glassy behavior of HAGBs (13,14). On the other hand, an amorphous HAGB would imply that its interfacial energy is insensitive to the grain misorientation angle (9, 15, 16). Nevertheless, GB mobility and diffusion, which have a strong dependence on the interfacial energy, are found to vary with the misorientation angle (17, 18). Also, given that GBs are only a few particle diameters wide at low temperatures, it is natural to expect confinement effects to play a key role in the dyna...

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“…Finally, we note the current proliferation of models for high angle grain boundaries which is appearing in the literature. Other models include the "secondary" (or "hierarchy of dislocations") GBD model (19)(20)(21), the ledge model (21,22) and the structural unit model (22).…”

Section: Discussionmentioning

confidence: 99%