Computer simulation of the elastically driven migration of a flat grain boundary

Zhang, Hao; Mendelev, Mikhail I.; Srolovitz, David J.

doi:10.1016/j.actamat.2004.02.005

Cited by 124 publications

(75 citation statements)

References 12 publications

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“…Stress-driven boundary motion has been observed experimentally, [29][30][31]50,53,54] as well as predicted by simulations [33,34] and theory. [55] Recent experimental results by Rupert et al [30] confirmed much of this theory in NC aluminum, although for monotonic tensile stresses.…”

Section: A Adiffusional Grain Growthmentioning

confidence: 68%

“…[28] Previous experimental observations of NC grain growth during plastic deformation, [29,30] indentation experiments [31] and as a result of fatigue loading [14,32] warrant serious consideration. The grain growth reported by Witney et al's [14] fatigue experiments on NC Cu presumably refers to modest overall grain growth, rather than discontinuous local coarsening observed in monotonic loading experiments by Gianola et al [29] In addition, several numerical models predicted evolution in NC grain structures under both elastic [33,34] and plastic [35][36][37] deformation. These previous observations on room-temperature mechanically driven grain growth lead one to suspect that NC metals may evolve such coarse grain structures during fatigue loading, and that the fatigue mechanisms may be influenced more by the evolved grain structure than by the initial structure.…”

Section: Introductionmentioning

confidence: 99%

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Anomalous Fatigue Behavior and Fatigue-Induced Grain Growth in Nanocrystalline Nickel Alloys

Boyce

Padilla

2011

Metall Mater Trans A

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Fatigue failure due to repetitive loading of metallic devices is a pervasive engineering concern. The present work reveals extraordinary fatigue resistance in nanocrystalline (NC) alloys, which appears to be associated with the small (<100 nm) grain size inhibiting traditional cyclic damage processes. In this study, we examine the fatigue performance of three electrodeposited NC Nibased metals: Ni, Ni-0.5Mn, and Ni-22Fe (PERMALLOY). When subjected to fatigue stresses at and above the tensile yield strength where conventional coarse-grained (CG) counterparts undergo low-cycle fatigue failure (<10 4 cycles to failure), these alloys exhibit exceptional fatigue lives (in some cases, >10 7 cycles to failure). Postmortem examinations show that failed samples contain an aggregate of coarsened grains at the crack initiation site. The experimental data and accompanying microscopy suggest that the NC matrix undergoes abnormal grain growth during cyclic loading, allowing dislocation activity to persist over length scales necessary to initiate a fatigue crack by traditional fatigue mechanisms. Thus, the present observations demonstrate anomalous fatigue behavior in two regards: (1) quantitatively anomalous when considering the extremely high stress levels needed to drive fatigue failure and (2) mechanistically anomalous in light of the grain growth process that appears to be a necessary precursor to crack initiation.

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Section: A Adiffusional Grain Growthmentioning

confidence: 68%

Section: Introductionmentioning

confidence: 99%

Anomalous Fatigue Behavior and Fatigue-Induced Grain Growth in Nanocrystalline Nickel Alloys

Boyce

Padilla

2011

Metall Mater Trans A

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“…Other grain-boundary ͑GB͒ mobility calculations, using different Cu potentials, have found similar values ͑24-31 kJ/ mol͒ for different types of GB. [34][35][36] Figure 5͑a͒ shows the number of annealing twins observed in an average cross section of the sample ͑the area is 716 nm 2 ͒ as a function of time for the annealing treatment at 800 K. The number of twins increases with time in a kinetics that closely resembles the kinetics of the observed grain growth. If the number of twins is divided by the number of grains in the same cross section of the sample, we can easily obtain an average number of twins per grain, which can be analyzed as a function of grain size.…”

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confidence: 95%

Annealing twins in nanocrystalline fcc metals: A molecular dynamics simulation

2007

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We report fully three-dimensional atomistic molecular dynamics studies of grain growth kinetics in nanocrystalline Cu of 5 nm average grain size. We observe the formation of annealing twins as part of the grain growth process. The grain size and energy evolution was monitored as a function of time for various temperatures, yielding an activation energy for the process. The atomistic mechanism of annealing twin formation from the moving boundaries is described. DOI: 10.1103/PhysRevB.75.184111 PACS number͑s͒: 61.72.Mm, 61.82.Rx Annealing twins in face-centered-cubic metals have been observed as early as 1897, 1-3 and are a prominent feature observed in routine metallography of these materials. The formation of these twins is usually associated with the process of grain growth that occurs during annealing at relatively high temperatures. Twin boundaries are usually flat and extend across an entire grain. The resulting density of twins after an annealing treatment is controlled by grainboundary energy, prior deformation, and resulting grain size. [4][5][6][7][8][9][10][11] The formation of annealing twins is a very common experimental observation; the fraction of annealing twins typically increases with annealing time and therefore with the amount of grain growth. Up to two to three twins per grain are typically observed, and it has been suggested that the nucleation and growth of twinning are mechanistically linked to anomalous grain growth. [12][13][14] In addition, it has been shown that imposed shear stresses during annealing of deformed fcc metals with low stacking fault energies tend to result in recrystallized microstructures containing higher fractions of twin boundaries than those annealed without an imposed shear stress. 13 This appears to be true also for materials deformed by severe plastic deformation where high residual shear stresses are present.The mechanisms by which annealing twins are formed are not completely understood. Current theories propose that accidents at growing grains and particularly faults on ͕111͖-type planes are responsible for the formation of annealing twins. [15][16][17][18] The models of twin formation generally require grain-boundary migration. In the model of Mahajan et al., 15 the nucleation of Shockley partial dislocations at growth accidents on ͕111͖ steps is associated with grain-boundary migration.In nanocrystalline materials, there is strong evidence that deformation occurs through emission of Shockley partial dislocations from grain boundaries which are absorbed in the opposing grain boundaries. These mechanisms based on partial dislocations lead to twinning when partial dislocations are emitted in adjacent ͕111͖-type planes. The deformation response of these materials has been studied using molecular dynamics simulation techniques, [19][20][21] and similar theoretical work can help in the detailed understanding of the process of twin formation during annealing treatments.In the present work, we report on relatively long molecular dynamics simulations of grain growt...

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“…1B, where x, y, and z axes define laboratory coordinates and [100], [010], and [001] define crystallographic axes), giving rise to a change in the elastic free energy of each grain (the crystals are elastically anisotropic) and a thermodynamic driving force for GB displacement. Computation details were described in our previous articles (21,22). Cooperative particle motion within the GB.…”

Section: Imentioning

confidence: 99%

Grain boundaries exhibit the dynamics of glass-forming liquids

Zhang

Srolovitz

Douglas

et al. 2009

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

175

160

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Polycrystalline materials are composites of crystalline particles or ''grains'' separated by thin ''amorphous'' grain boundaries (GBs). Although GBs have been exhaustively investigated at low temperatures, at which these regions are relatively ordered, much less is known about them at higher temperatures, where they exhibit significant mobility and structural disorder and characterization methods are limited. The time and spatial scales accessible to molecular dynamics (MD) simulation are appropriate for investigating the dynamical and structural properties of GBs at elevated temperatures, and we exploit MD to explore basic aspects of GB dynamics as a function of temperature. It has long been hypothesized that GBs have features in common with glass-forming liquids based on the processing characteristics of polycrystalline materials. We find remarkable support for this suggestion, as evidenced by string-like collective atomic motion and transient caging of atomic motion, and a non-Arrhenius GB mobility describing the average rate of large-scale GB displacement.glass formation ͉ grain-boundary mobility ͉ molecular dynamics ͉ polycrystalline materials ͉ string-like collective motion M ost technologically important materials are polycrystalline in nature (1), and it is appreciated that the grain boundaries (GBs) of these materials, the interfacial region separating the crystal grains (see Fig. 1A), significantly influence the properties of this broad class of materials (2). In particular, the dynamical properties of GBs, such as the GB mobility (M), play an important role in the plastic deformation and evolution of microstructure during material processing and service (3). † The atomic organization in the GBs represents a compromise between the ordering effects of adjacent grains, and ''packing frustration'' [or reduced packing efficiency (6)] is also characteristic of glass-forming (GF) fluids, in which particle ordering is likewise limited in range (7). This simple observation leads us to expect similarities between the dynamics of GBs and GF fluids, and below we provide evidence for this relationship. By implication, GB migration should then be sensitive to impurities, geometrical confinement, and applied stresses-basically any factor that affects particle-packing efficiency (8-10). To illustrate this point and test our perspective of GB dynamics, we quantitatively interpret differences in the effect of large tensile and compressive deformations on M in terms of measures of cooperative atomic motion drawn from the physics of GF fluids.Nearly 100 years ago, Rosenhain and Ewen (11) suggested that metal grains in cast iron were ''cemented'' together by a thin layer of ''amorphous'' (i.e., noncrystalline) material ''identical with or at least closely analogous to the condition of a greatly undercooled liquid.'' Although this conceptual model was able to rationalize processing characteristics of ferritic materials (11), it was not possible to validate it at the time through direct observation or simulation. Sixty year...

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Computer simulation of the elastically driven migration of a flat grain boundary

Cited by 124 publications

References 12 publications

Anomalous Fatigue Behavior and Fatigue-Induced Grain Growth in Nanocrystalline Nickel Alloys

Anomalous Fatigue Behavior and Fatigue-Induced Grain Growth in Nanocrystalline Nickel Alloys

Annealing twins in nanocrystalline fcc metals: A molecular dynamics simulation

Grain boundaries exhibit the dynamics of glass-forming liquids

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