Deformation twinning during nanoindentation of nanocrystalline Ta

Wang, Y. M.; Hodge, Andrea M.; Biener, Juergen; Hamza, A. V.; Barnes, David; Liu, Kai; Nieh, T.G.

doi:10.1063/1.1883335

Cited by 84 publications

(68 citation statements)

References 22 publications

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“…With the help of Eqs. (19)- (21) in Section 4.2, which describe the dislocation reactions of Da, the aD reactions for transmission across the twin boundary can be described by:…”

Section: Leading 90°partial Ad Transmits Across the Twin Boundarymentioning

confidence: 99%

“…Since deformation twinning usually occurs simultaneously with the slip of perfect and partial dislocations, interactions between twins and gliding dislocations inevitably occur at twin boundaries. Nanocrystalline fcc metals have been found to deform via twinning more readily than their coarse grained counterparts [11][12][13][14][15][16][17][18][19][20][21][22]. This increases the probability of interactions between dislocations and twins in nanocrystalline fcc metals.…”

Section: Introductionmentioning

confidence: 99%

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Dislocation–twin interactions in nanocrystalline fcc metals

et al. 2011

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Dislocation interaction with and accumulation at twin boundaries have been reported to significantly improve the strength and ductility of nanostructured face-centered cubic (fcc) metals and alloys. Here we systematically describe plausible dislocation interactions at twin boundaries. Depending on the characteristics of the dislocations and the driving stress, possible dislocation reactions at twin boundaries include cross-slip into the twinning plane to cause twin growth or de-twinning, formation of a sessile stair-rod dislocation at the twin boundary, and transmission across the twin boundary. The energy barriers for these dislocation reactions are described and compared.

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“…With the help of Eqs. (19)- (21) in Section 4.2, which describe the dislocation reactions of Da, the aD reactions for transmission across the twin boundary can be described by:…”

Section: Leading 90°partial Ad Transmits Across the Twin Boundarymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dislocation–twin interactions in nanocrystalline fcc metals

et al. 2011

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“…The mechanical properties of nanocrystalline ͑nc͒ materials are controlled by their deformation mechanisms, 1 which include partial dislocation emission from grain boundaries ͑GBs͒, 2-10 deformation twinning, [9][10][11][12][13][14][15][16][17][18][19][20] full dislocations, 3,5,7 GB sliding, 3,11-13 and grain rotation. 11,14 Basing on generalized planar fault energy ͑GPFE͒ curves, molecular dynamics ͑MD͒ simulations predicted that nc Ni prefers to deform by extended partials, rather than twinning.…”

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confidence: 99%

Partial-dislocation-mediated processes in nanocrystalline Ni with nonequilibrium grain boundaries

Zhu

2006

Applied Physics Letters

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The partial-dislocation-mediated processes have so far eluded high-resolution transmission electron microscopy studies in nanocrystalline ͑nc͒ Ni with nonequilibrium grain boundaries. It is revealed that the nc Ni deformed largely by twinning instead of extended partials. The underlying mechanisms including dissociated dislocations, high residual stresses, and stress concentrations near stacking faults are demonstrated and discussed. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2227639͔The mechanical properties of nanocrystalline ͑nc͒ materials are controlled by their deformation mechanisms, 1 which include partial dislocation emission from grain boundaries ͑GBs͒, 2-10 deformation twinning, 9-20 full dislocations, 3,5,7 GB sliding, 3,11-13 and grain rotation. 11,14 Basing on generalized planar fault energy ͑GPFE͒ curves, molecular dynamics ͑MD͒ simulations predicted that nc Ni prefers to deform by extended partials, rather than twinning. 5 The two energies on the GPFE curves, the unstable stacking fault energy ͑SFE͒ ␥ usf and the unstable twin fault energy ␥ utf , are believed to play critical roles in the activation of extended partials and twining. 5 However, a recent study indicates that the ␥ usf and ␥ utf values obtained from GPFE curves vary significantly with the models used for their calculation and it is not clear if these values even qualitatively agree with the real values, 21 which so far cannot be experimentally measured. A recent experimental study 22 revealed the formation of both stacking faults and deformation twins in electrodeposited Ni, which has GBs not far from equilibrium and those used in MD simulations.Nanomaterials often have nonequilibrium GBs with high densities of extrinsic ͑extra͒ dislocations. [23][24][25] This is especially true for those nc metals and alloys produced by severe plastic deformation. 26 It has been claimed that the GPFE curves are not applicable to these nc metals and alloys because partial dislocations already exist at/near nonequilibrium GBs and therefore do not need to be nucleated. 27,28 In other words, since the ␥ usf and ␥ utf only affect the nucleation process of the extended partial and the first twin partial, they should not affect the nc metals and alloys with nonequilibrium GBs. However, experimental evidence is still lacking to support such a claim.The objective of this work is to study the partialdislocation-mediated processes in nanomaterials with nonequilibrium GBs. We chose to use nc Ni produced by surface mechanical attrition treatment ͑SMAT͒ ͑Ref. 29͒ in this study because Ni has been extensively studied by MD simulations and experiments, and SMAT can produce nc Ni with impurity-free nonequilibrium GBs.A Ni plate with a purity of 99.998% was subjected to SMAT at room temperature to produce a layer of nc Ni. 30 Extensive high-resolution electron microscopy ͑HREM͒ observations revealed that at the depth of 27 m from the surface, the nc Ni has grain sizes in the range of 20-100 nm. The grain size is found to affect twinning propensity: twin...

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“…[1][2][3][4][5][6][7] Deformation twins and stacking faults, indicating the presence of dislocation activities in nc grains and especially the operation of partial dislocation mediated processes, were observed in Al, [1][2][3] Cu, 4 Pd, 5,6 and Ta. 7 The nc-Al and nc-Pd cases are especially interesting, as these fcc metals have high stacking fault energies and little or no chance of undergoing deformation twinning in their coarse-grained form ͑conventional fcc Cu, in comparison, is known to twin when deformed at low temperatures and/or high strain rates͒. However, there appears to be a glaring contradicting example: recent in situ x-ray diffraction studies of fcc nc-Ni subjected to tensile deformation showed no irreversible peak broadening.…”

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confidence: 99%

Deformation twinning mechanisms in nanocrystalline Ni

2006

Applied Physics Letters

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Extensive transmission electron microscopy examinations confirm that twinning does occur upon large plastic deformation in nanocrystalline Ni, for which no sign of deformation twinning was found in previous tensile tests. Compelling evidence has been obtained for several twinning mechanisms that operate in nanocrystalline grains, with the grain boundary emission of partial dislocations determined as the most proficient.

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Deformation twinning during nanoindentation of nanocrystalline Ta

Cited by 84 publications

References 22 publications

Dislocation–twin interactions in nanocrystalline fcc metals

Dislocation–twin interactions in nanocrystalline fcc metals

Partial-dislocation-mediated processes in nanocrystalline Ni with nonequilibrium grain boundaries

Deformation twinning mechanisms in nanocrystalline Ni

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