Untangling dislocation and grain boundary mediated plasticity in nanocrystalline nickel

Lohmiller, Jochen; Grewer, Manuel; Braun, Christian; Kobler, Aaron; Kübel, Christian; Schüler, Kerstin; Honkimäki, V.; Hahn, Horst; Kraft, O.; Birringer, R.; Gruber, Patric A.

doi:10.1016/j.actamat.2013.10.071

Cited by 60 publications

(22 citation statements)

References 44 publications

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“…Overall, the diverse evolution of the respective deformation shares appears as being just a consequence of a complex hierarchical order of onset/nucleation and upholding stresses of different deformation mechanisms, the presence and degree of activity of which strongly depends on grain size. For example, in a recent study of NC Ni with a grain size of 30 nm, a strain share of about 40 % could be assigned to dislocation activity [31]. We finally conjecture that the state of the GB core structure, whether in relaxed (low-excess-energy) or as-prepared (high-excess-energy) configuration, should also have a decisive effect on the share and onset stresses of the above discussed deformation modes.…”

Section: Discussionmentioning

confidence: 74%

“…To analyze the microstrain and grain size evolution, we make use of the single line method, introduced by de Keijser et al [39], which allows to extract separate values of grain size and microstrain for each {hkl}-reflection. The widely used Williamson-Hall approach led to poorly conditioned results, certainly due to the elastic anisotropy of PdAu but also related to the fact that the diffracted intensity has been recorded in transmission geometry, implying a slight variation of the orientation of the scattering vector with the diffraction angle which renders the Williamson-Hall approach intractable; further technical details can be found in [31]. Using the single line method, deconvolution of size and microstrain contributions results in the following equations for the volume averaged grain size D vol and the microstrain e…”

Section: Integral Peak Width: Microstrain and Grain Size Evolutionmentioning

confidence: 99%

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Anatomizing deformation mechanisms in nanocrystalline Pd 90 Au 10

Grewer

Braun

Deckarm

et al. 2017

Mechanics of Materials

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We utilized synchrotron-based in-situ diffraction and dominant shear deformation to identify, dissect, and quantify the relevant deformation mechanisms in nanocrystalline Pd 90 Au 10 in the limiting case of grain sizes at or below 10 nm. We could identify lattice and grain boundary elasticity, shear shuffling operating in the core region of grain boundaries, stress driven grain boundary migration, and dislocation shear along lattice planes to contribute, however, with significantly different and nontrivial stress-dependent shares to overall deformation. Regarding lattice elasticity, we find that Hookean linear elasticity prevailed up to the maximal stress value of ≈ 1.6 GPa. Shear shuffling that propagates strain at/along grain boundaries increases progressively with increasing load to carry about two thirds of the overall strain in the regime of macroplasticity. Stress driven grain boundary migration requires overcoming a threshold stress slightly below the yield stress of ≈ 1.4 GPa and contributes a share of ≈ 10 % to overall strain. Appreciable dislocation activity begins at a stress value of ≈ 0.9 GPa to then increase and eventually propagate a maximal share of ≈ 15 % to overall strain. In the stress regime below 0.9 GPa, which is characterized by a markedly decreasing tangent modulus, shear shuffling and lattice-and grain boundary elasticity operate exclusively. The material response in this regime seems indicative of nonlinear viscous behavior rather than being correlated with work-or strain hardening as observed in conventional fcc metals.

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Section: Discussionmentioning

confidence: 74%

Section: Integral Peak Width: Microstrain and Grain Size Evolutionmentioning

confidence: 99%

Anatomizing deformation mechanisms in nanocrystalline Pd 90 Au 10

Grewer

Braun

Deckarm

et al. 2017

Mechanics of Materials

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“…The texture consists of six-fold symmetries with maxima intensities for (111), (200), (311), and (222) reflections in the tensile direction and minima in intensity for the (220) reflection. The development of texture in this region is indicative of dislocation-mediated plasticity [11][12][13] and in this case is likely formed by rotation of the columnar grains into directions of preferred slip. [13][14][15] Cross-sectional FIB micrographs at the corresponding locations in Region I are shown in Figures 2(a2) and 2(b2).…”

mentioning

confidence: 92%

Temperature-dependent strain localization and texture evolution of highly nanotwinned Cu

Furnish

Lohmiller

Gruber

et al. 2013

Applied Physics Letters

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Strong differences in the plastic strain and texture development in high purity nanotwinned copper foils deformed to failure in tension at ambient and liquid nitrogen (LN) temperatures have been observed. High energy microdiffraction patterns for the room temperature (RT) sample showed two distinct deformation regions relative to its fracture surface: d < 500 μm and d > 500 μm; while for the sample deformed at 77 K, three distinct regions were observed: d < 120 μm, 120 μm < d < 1550 μm, and d > 1550 μm. The localized plastic deformation in the RT tensile test and the increased ductile deformation at LN temperature are discussed in terms of the dualistic nanotwins plus micro-scale columnar grain structure.

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“…Deformation mechanisms operating in nanocrystalline metals sensitively depend on the average grain size and grain size distribution [1]. In contrast to coarse-grained polycrystalline metals, where plastic strain is predominantly carried by dislocations, grain-boundary-mediated deformation processes (including sliding and shuffling mechanisms) become increasingly relevant with decreasing grain size.…”

Section: Introductionmentioning

confidence: 99%

From metallic glasses to nanocrystals: Molecular dynamics simulations on the crossover from glass-like to grain-boundary-mediated deformation behaviour

Brink

Albe

2018

Acta Materialia

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Nanocrystalline metals contain a large fraction of high-energy grain boundaries, which may be considered as glassy phases. Consequently, with decreasing grain size, a crossover in the deformation behaviour of nanocrystals to that of metallic glasses has been proposed. Here, we study this crossover using molecular dynamics simulations on bulk glasses, glass-crystal nanocomposites, and nanocrystals of Cu 64 Zr 36 with varying crystalline volume fractions induced by long-time thermal annealing. We find that the grain boundary phase behaves like a metallic glass under constraint from the abutting crystallites. The transition from glass-like to grain-boundary-mediated plasticity can be classified into three regimes: (1) For low crystalline volume fractions, the system resembles a glass-crystal composite and plastic flow is localised in the amorphous phase; (2) with increasing crystalline volume fraction, clusters of crystallites become jammed and the mechanical response depends critically on the relaxation state of the glassy grain boundaries; (3) at grain sizes ≥ 10 nm, the system is jammed completely, prohibiting pure grain-boundary plasticity and instead leading to co-deformation. We observe an inverse Hall-Petch effect only in the second regime when the grain boundary is not deeply relaxed. Experimental results with different grain boundary states are therefore not directly comparable in this regime.

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Untangling dislocation and grain boundary mediated plasticity in nanocrystalline nickel

Cited by 60 publications

References 44 publications

Anatomizing deformation mechanisms in nanocrystalline Pd 90 Au 10

Anatomizing deformation mechanisms in nanocrystalline Pd 90 Au 10

Temperature-dependent strain localization and texture evolution of highly nanotwinned Cu

From metallic glasses to nanocrystals: Molecular dynamics simulations on the crossover from glass-like to grain-boundary-mediated deformation behaviour

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