“Bulk” Nanocrystalline Metals: Review of the Current State of the Art and Future Opportunities for Copper and Copper Alloys

Tschopp, Mark A.; Murdoch, Heather A.; Kecskes, Laszlo J.; Darling, Kristopher A.

doi:10.1007/s11837-014-0978-z

Cited by 83 publications

(44 citation statements)

References 210 publications

(325 reference statements)

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“…As a consequence, a maximum threshold value of yield stress or hardness is generally reached at certain grain size level for a given nanocrystalline metal or alloy. Numerous reports show that the transition of positive to negative slope in the HP relationship is around 10-40 nm for varied nanocrystalline metals and alloys [6][7][8], such as Al [9][10][11], Fe [12], Cu [6,13,14], Cu-Ta [15], Ni [6], Ni-P [13], Zr [16], and Zn [17] among others.…”

Section: Introductionmentioning

confidence: 99%

“…In general, grain boundaries (and twin boundaries in some cases, such as in the nanocrystalline Al [18,19] and Cu [14,15] systems) and dislocation motion play an important role in elastic and plastic deformation processes, which are crucial factors in controlling the mechanical properties of nanocrystalline metals, particularly at the nanoscale [18][19][20]. Below certain grain sizes, most of the dislocation generation and storage takes place at the grain boundary regions as opposed to the larger grain interior regions [15].…”

Section: Introductionmentioning

confidence: 99%

“…Below certain grain sizes, most of the dislocation generation and storage takes place at the grain boundary regions as opposed to the larger grain interior regions [15]. In addition, with the reduction of grain size from microscale to nanoscale, the dislocation motion becomes strongly size dependent and both dynamic recovery and annihilation of dislocations increase [15], which ultimately limits the capacity for dislocation storage at fine-grained nanocrystalline metals.…”

Section: Introductionmentioning

confidence: 99%

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Tensile nanomechanics and the Hall-Petch effect in nanocrystalline aluminium

Dávila

2018

Materials Science and Engineering: A

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A B S T R A C TThis work carries out comprehensive classical molecular dynamics simulations of uniaxial tensile deformation for nanocrystalline Al samples with a broad range of different mean grain sizes. The largest nanocrystalline Al sample has a mean grain size of about 30 nm and contains over 100 millions atoms in the modeling system. The grain size dependence of yield stress and the atomic fraction of dislocations are quantified and the size dependence tensile nanomechanics are also revealed. Deformation twinning and grain boundary migration are observed as main mechanisms of tensile deformation in the nanocrystalline Al. In particular, the complete HallPetch relationship for the nanocrystalline Al bulk is determined for the first time in this study, from which three distinct regions are identified including the normal, inverse, and extended regions in the Hall-Petch relationship. We expect these findings will provide useful insights in the nanomechanics of nanocrystalline Al. The quantitation analyses on dislocations and mechanical properties may facilitate the design and development of high strength nanocrystalline Al and Al based alloys as well as future testing procedures for promising structural and transportation applications.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Tensile nanomechanics and the Hall-Petch effect in nanocrystalline aluminium

Dávila

2018

Materials Science and Engineering: A

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“…For example, nanocrystalline Al, Sn, Pb, and Mg are subjected to grain growth even at room temperature [5][6][7]. There are two general approaches to stabilize nanocrystalline materials against grain growth [8][9][10][11]. First, kinetic stabilization by the solute-drag effects and/or Zener (particle) pinning can slow down grain boundary (GB) migration [12][13][14], which become less effective at high temperatures.…”

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confidence: 99%

Stabilization of nanocrystalline alloys at high temperatures via utilizing high-entropy grain boundary complexions

et al. 2016

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Multicomponent alloying can be utilized to enhance the thermal stability of nanocrystalline alloys. The grain boundary energy can be reduced significantly via both bulk and grain-boundary high-entropy effects with increasing temperature at/within the solid solubility limit, thereby reducing the thermodynamic driving force for grain growth. Moreover, grain boundary migration can be hindered by sluggish kinetics. Although nanocrystalline metals can exhibit superior properties such as high strength and hardness [1][2][3][4], their applications are often hindered by the extreme susceptibility to grain growth. For example, nanocrystalline Al, Sn, Pb, and Mg are subjected to grain growth even at room temperature [5][6][7]. There are two general approaches to stabilize nanocrystalline materials against grain growth [8][9][10][11]. First, kinetic stabilization by the solute-drag effects and/or Zener (particle) pinning can slow down grain boundary (GB) migration [12][13][14], which become less effective at high temperatures. Second, thermodynamic stabilization can be achieved by reducing the GB energy (γ GB ) via solute segregation (a.k.a. GB adsorption) to reduce the thermodynamic driving force for grain growth. Specifically, Weismuller originally proposed that an "equilibrium" grain size can be reached when the effective γ GB vanishes [15,16]. Yet, Kirchheim [17] showed that the equilibriumgrain-size binary nanocrystalline alloys generally represent metastable states in supersaturated regions if (and only if) the precipitation is hindered kinetically. In such cases, the kinetic inhibition of the precipitation also becomes more difficult with increasing temperature, triggering abrupt grain growth. These challenges motivate the present study to develop and test new theories and strategies to enhance the thermal stability of nanocrystalline alloys at high temperatures via utilizing highentropy GB complexions (where the term "complexion" refers to an interfacial "phase" that is thermodynamically two-dimensional [18] The Gibbs adsorption theory states:where S XS (entropy) and Γ i (adsorption) are the GB excess quantities, T is temperature, and μ i is the chemical potential of the i-th element. Eq.(1) implies that the GB energy (γ GB ) can be reduced by segregation at a constant T and this effect can be enhanced for multicomponent (high-entropy) GBs under certain conditions. We should note that generally (∂γ GB /∂ T) P , X i N 0 for a specimen of a constant bulk composition (X Bulk i ) due to thermally-induced desorption. In a recent article [26], we proposed that a high-entropy GB effect can be achieved for a saturated specimen (in equilibrium with precipitates), when the bulk composition moves long the solvus line, where the solutes' bulk chemical potentials are pinned by the precipitates so that (∂ γ GB / ∂ T) P , X Bulk i on solvus ≈ (∂ γ GB /∂ T) P , μ i = − S XS ; thus, γ GB can be reduced with increasing temperature for a high-entropy GB with positive and

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“…[8] Fundamental changes in deformation mechanisms are also known to cause many other intriguing and unexpected physical responses of NC metals, including altered strain rate and pressure dependence of deformation, [9] superplasticity, [10] and lowtemperature creep, [11] to name a few. [12] Generally, these unique deviations in behavior are solely attributed to a continual reduction in grain size and an increase in the fraction of grain boundaries and triple junctions, which leads to experimentally reported mechanisms of deformation twinning, GB rotation/sliding and viscous flow. [13][14][15] Plastic instability [2,3,16,17] due to loss in the strain hardening behavior and grain growth (under both monotonic and cyclic loading) [18][19][20] have also been observed in various pure NC materials at small grain sizes.…”

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confidence: 99%