Characterization of atomic motion governing grain boundary migration

Zhang, Hao; Srolovitz, David J.; Douglas, Jack F.; Warren, James A.

doi:10.1103/physrevb.74.115404

Cited by 70 publications

(88 citation statements)

References 32 publications

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“…Instead, we chose to exploit the analogy between HAGBs and glass-forming liquids (27,40). For HAGBs, the rate-controlling events for migration are single-atom hops across the boundary plane (47,48) and the characteristic time associated with these hops is the cage-breaking time t*. We extracted t* from the inflection point in the mean first passage time τðrÞ (48), defined as the average time taken by a particle to traverse a distance r for the first time.…”

Section: Resultsmentioning

confidence: 99%

Directional grain growth from anisotropic kinetic roughening of grain boundaries in sheared colloidal crystals

Gokhale

Nagamanasa

Santhosh

et al. 2012

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

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The fabrication of functional materials via grain growth engineering implicitly relies on altering the mobilities of grain boundaries (GBs) by applying external fields. Although computer simulations have alluded to kinetic roughening as a potential mechanism for modifying GB mobilities, its implications for grain growth have remained largely unexplored owing to difficulties in bridging the widely separated length and time scales. Here, by imaging GB particle dynamics as well as grain network evolution under shear, we present direct evidence for kinetic roughening of GBs and unravel its connection to grain growth in driven colloidal polycrystals. The capillary fluctuation method allows us to quantitatively extract shear-dependent effective mobilities. Remarkably, our experiments reveal that for sufficiently large strains, GBs with normals parallel to shear undergo preferential kinetic roughening, resulting in anisotropic enhancement of effective mobilities and hence directional grain growth. Single-particle level analysis shows that the mobility anisotropy emerges from strain-induced directional enhancement of activated particle hops normal to the GB plane. We expect our results to influence materials fabrication strategies for atomic and block copolymeric polycrystals as well.colloids | grain boundary migration | anisotropic grain growth T he motion and rearrangement of grain boundaries (GBs) is central to our understanding of recrystallization (1), grain growth and its stagnation (2), and superplasticity (3) in a broad class of polycrystalline materials including metals (4), ceramics (5), colloidal crystals (6), and block copolymers (7,8). Polycrystals are pervasive as engineering materials and elucidating mechanisms that determine the structure and dynamics of their GBs continue to be a central goal of materials research (9). Advances in computer simulation methods (2, 10, 11) and experiments (12, 13) have provided substantial insights into the microscopic origins of these mechanisms. In conventional materials, nevertheless, establishing a direct link between the dynamics at the single/few atom length scale and the collective behavior of the many thousands of atoms that constitute GBs and grains poses a serious challenge (14).A bridging of length scales is vital for grain growth studies. The key parameter in grain growth and its stagnation is the mobility of GBs, which is determined by their roughness (2, 15). Although transmission electron microscopy (TEM) is well-suited for grain growth measurements, no technique exists that can nonintrusively quantify the atomic scale roughness of buried GBs (14). These experimental shortcomings are compounded in driven polycrystals, which assume practical significance in the fabrication of functional materials via grain growth engineering (2, 7). Driven GBs (16) are thought to kinetically roughen (17), which may result in significantly enhanced mobilities (15) and influence grain growth. Further, in nanocrystalline materials, which often possess superior mechanical propert...

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Section: Resultsmentioning

confidence: 99%

Directional grain growth from anisotropic kinetic roughening of grain boundaries in sheared colloidal crystals

Gokhale

Nagamanasa

Santhosh

et al. 2012

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

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“…Such atoms were identified on the basis of their mobility, relatively high with respect to the others, and their capability of remaining neighbors after motion has occurred. [32][33][34] The condition 0.35r nn Ͻ ͉r i ͑͒ − r i ͑0͉͒ Ͻ 0.86r min was used to identify mobile atoms i. Here r i ͑t͒ represents the ith atom position at time t, r nn is the distance of nearest neighbors indicated by the global pair correlation function ͑PCF͒ ͑Ref.…”

Section: Molecular Dynamics Simulationsmentioning

confidence: 99%

“…Mobile atoms i and j remaining neighbors in correlated displacements were instead defined as the atomic species satisfying the condition min͓͉r i ͑͒ − r j ͑0͉͒ , ͉r j ͑͒ − r i ͑0͉͔͒ Ͻ 0.43r nn . 34 This condition is based on the assumption, supported by numerical evidence, 34 that in most cases of collective behavior atomic species move in strings. The condition above assures precisely that, after a displacement into the string, the atom i occupies the position formerly occupied by the atom j or vice versa.…”

Section: Molecular Dynamics Simulationsmentioning

confidence: 99%

“…The displacement length threshold of 0.43r nn was chosen to be less than an interatomic distance to distinguish correlated displacements in the string from different mechanism of displacement. 34 The numerical coefficients used are able to effectively separate cooperative motions from thermal vibrations and vacancy-mediated exchanges of atoms. 34 Similar results are obtained when slightly different values are used.…”

Section: Molecular Dynamics Simulationsmentioning

confidence: 99%

“…34 The numerical coefficients used are able to effectively separate cooperative motions from thermal vibrations and vacancy-mediated exchanges of atoms. 34 Similar results are obtained when slightly different values are used.…”

Section: Molecular Dynamics Simulationsmentioning

confidence: 99%

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Numerical investigation of the stability of Ag-Cu nanorods and nanowires

et al. 2008

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Molecular dynamics simulations have been employed to investigate thermally-induced phase separation processes in nanometer-sized Ag 50 Cu 50 rods and wires. In the absence of concentration gradients, the mechanism underlying the system decomposition consists of two stages. Roughly below 260 K, the thermal response is governed by the displacement of individual surface atoms. Above such temperature, phase separation proceeds via cooperative rearrangements involving also bulklike atomic species. The result is the formation of systems with an Ag-rich phase segregated at the surface. Significantly different thermal responses are obtained in the presence of concentration gradients perpendicular or parallel to the wire axis. First, the phase separation process is favored and takes place at lower temperatures. Second, an almost complete decomposition of the system in Ag-and Cu-rich domains is obtained and not the surface segregation of the Ag-rich phase. The decomposition is also accompanied by a considerable distortion of the originally regular nanowire shape.

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Similarities of the Collective Interfacial Dynamics of Grain Boundaries and Nanoparticles to Glass‐Forming Liquids

Zhang

Douglas²

2013

Liquid Polymorphism

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Characterization of atomic motion governing grain boundary migration

Cited by 70 publications

References 32 publications

Directional grain growth from anisotropic kinetic roughening of grain boundaries in sheared colloidal crystals

Directional grain growth from anisotropic kinetic roughening of grain boundaries in sheared colloidal crystals

Numerical investigation of the stability of Ag-Cu nanorods and nanowires

Similarities of the Collective Interfacial Dynamics of Grain Boundaries and Nanoparticles to Glass‐Forming Liquids

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