Density of grain boundaries and plasticity size effects: A discrete dislocation dynamics study

Kumar, Rajiv; Nicola, Lucia; Giessen, van der Erik

doi:10.1016/j.msea.2009.08.072

Cited by 44 publications

(29 citation statements)

References 23 publications

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“…The Bauschinger strain B remains low for pancakelike grains with small AR, whereas it attains 20% or more of the yield strain when the grains are equiaxed or even needlelike ͑ARտ 1͒. These observations link-up with findings in previous DDP studies of thin films under tension 4,9 that needlelike grains exhibit a high hardening rate due to the development of dislocation pile-ups against GBs. These pile-ups are responsible for the storage of energy, which assists reverse plastic deformation during unloading.…”

Section: A Predicted Besupporting

confidence: 78%

“…16͑a͒ by plotting B as a function of the density of GBs ͑defined as From this figure, two observations are made. First, the correlation between B and GB ͑n͒ is not as good as that between yield strength and GB density as reported by Kumar et al 9 The data for single-layer films, in fact, do not even reveal a trend. The latter can be attributed to the fact that for n =1 the GB density parameter lacks any information about the film thickness and thus makes it hard to compare films with different thickness.…”

Section: Discussionmentioning

confidence: 62%

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Bauschinger effect in unpassivated freestanding thin films

Shishvan

Nicola

Giessen

2010

Journal of Applied Physics

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Two-dimensional ͑2D͒ discrete dislocation plasticity simulations are carried out to investigate the Bauschinger effect ͑BE͒ in freestanding thin films. The BE in plastic flow of polycrystalline materials is generally understood to be caused by inhomogeneous deformation during loading, leading to residual stress upon unloading. This inhomogeneity can be caused by dislocation pile-ups, variations in texture, grain orientations, and grain size. To study the BE, columnar-grained films as well as films with multiple grains across the thickness are considered. The film is modeled in a 2D framework by a unit cell consisting of an array of grains with different orientation. In order to capture the interaction among grains, we motivate and explore the use of an affine deformation assumption on the grain level to mimic the three-dimensional geometry in this framework. It is shown that the dispersion of grain size in a film together with the size-dependence of yield strength leads to significant BEs in bare films. Quantitative comparison of simulations with experimental data is provided.

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Section: A Predicted Besupporting

confidence: 78%

Section: Discussionmentioning

confidence: 62%

Bauschinger effect in unpassivated freestanding thin films

Shishvan

Nicola

Giessen

2010

Journal of Applied Physics

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“…This is partly due to increase in grain coarsening which leads to an increase in the grain boundary area which increases the amount of energy required for the movement of dislocations required to cause fracture [34][35][36] . Thus, the material can withstand a higher plastic deformation before the final fracture.…”

Section: µMmentioning

confidence: 99%

Effect of heat treatment on some mechanical properties of 7075 aluminium alloy

et al. 2012

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This paper reports the effects of annealing and age hardening heat treatments on the microstructural morphology and mechanical properties of 7075 Al alloy. The material was cast in the form of round cylindrical rods inside green sand mould from where some samples were rapidly cooled by early knockout and others gradually cooled to room temperature. From the samples that were gradually cooled some were annealed while others were age hardened. Both the as-cast in each category and heat treated samples were subjected to some mechanical tests and the morphology of the resulting microstructures were characterised by optical microscopy. From the results obtained there is formation of microsegregations of MgZn 2 during gradual solidification which was not present during rapid cooling. It was also found out that age hardening and annealing heat treatment operation eliminated these microsegregations and improve mechanical properties of 7075 Al alloy. It is concluded that microsegregation can be eliminated by rapid solidification and appropriate heat treatment process.

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“…For the same reasons, one would expect climb to be more prominent when the grain size is smaller or the density of dislocation sources is reduced. 12,13 In our 2D simulations, dislocation sources and obstacles are regarded as static entities, while in reality they evolve as the dislocation structure changes. Any effects due to the curvature of the dislocations are also not taken into account.…”

Section: Resultsmentioning

confidence: 99%

“…While the two-dimensional formulation clearly cannot capture all of the physics, it allows for the modeling of realistic numbers of dislocations and microstructures, and it has been quite successful at simulating the behavior of thin films over a range of microstructures. [11][12][13][14][15][16][17][18][19] Most previous DDD studies [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] have been limited to low temperatures. Since diffusion of point defects is negligible at low temperatures, the movement of dislocations is limited to glide.…”

Section: Introductionmentioning

confidence: 99%

Dislocation climb in two-dimensional discrete dislocation dynamics

Davoudi

Nicola

Vlassak

2012

Journal of Applied Physics

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In this paper, dislocation climb is incorporated in a two-dimensional discrete dislocation dynamics model. Calculations are carried out for polycrystalline thin films, passivated on one or both surfaces. Climb allows dislocations to escape from dislocation pile-ups and reduces the strainhardening rate, especially for fully passivated films. Within the framework of this model, climb modifies the dislocation structures that develop during plastic deformation and results in the formation of pile-ups on slip planes that do not contain any dislocation sources. V C 2012 American Institute of Physics. [http://dx

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Density of grain boundaries and plasticity size effects: A discrete dislocation dynamics study

Cited by 44 publications

References 23 publications

Bauschinger effect in unpassivated freestanding thin films

Bauschinger effect in unpassivated freestanding thin films

Effect of heat treatment on some mechanical properties of 7075 aluminium alloy

Dislocation climb in two-dimensional discrete dislocation dynamics

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