Percolating network of ultrafast transport channels in severely deformed nanocrystalline metals

Divinski, Sergiy V.; Ribbe, Jens; Reglitz, Gerrit; Estrin, Yuri; Wilde, Gerhard

doi:10.1063/1.3211966

Cited by 37 publications

(30 citation statements)

References 41 publications

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“…The extremely fast tracer penetration in severely deformed pure Ni is consistent with the previous results of radiotracer diffusion measurements on ultra-fast transport in SPDprocessed pure Cu [122][123][124] and Cu-based alloys [125][126] Such an observation substantiates the complexity of "non-equilibrium GBs". We have to admit that in addition to common parameters required to specify a relaxed high-angle grain boundary (i.e.…”

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confidence: 79%

Grain boundaries in ultrafine grained materials processed by severe plastic deformation and related phenomena

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Wilde

Divinski

et al. 2012

Materials Science and Engineering: A

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Grain boundaries in ultrafine grained (UFG) materials processed by severe plastic deformation (SPD) are often called "non-equilibrium" grain boundaries. Such boundaries are characterized by excess grain boundary energy, presence of long range elastic stresses and enhanced free volumes. These features and related phenomena (diffusion, segregation, etc.) have been the object of intense studies and the obtained results provide convincing evidence of the importance of a non-equilibrium state of high angle grain boundaries for UFG materials with unusual properties. The aims of the present paper are first to give a short overview of this research field and then to consider tangled, yet unclear issues and outline the ways of oncoming studies. A special emphasis is given on the specific structure of grain boundaries in ultrafine grained materials processed by SPD, on grain boundary segregation, on interfacial mixing linked to heterophase boundaries and on grain boundary diffusion. The connection between these unique features and the mechanical properties or the thermal stability of the ultrafine grained alloys is also discussed.

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supporting

confidence: 79%

Grain boundaries in ultrafine grained materials processed by severe plastic deformation and related phenomena

Sauvage

Wilde

Divinski

et al. 2012

Materials Science and Engineering: A

488

219

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“…But, even faster paths are observed in SPD processed metals with a hierarchy of internal interfaces with respect to their diffusion rates [32]. The most important and intriguing finding of these studies is the presence of (percolating) porosity, which is formed even in such highly ductile metals like ECAP-deformed pure copper [29]. This percolating internal porosity, which is reported in certain well-documented cases such as room-temperature ECAP-deformed pure Cu [34] and Cu-based alloys [35] or HPT processed pure Cu [36] at room temperature, represents the fastest diffusion paths in an otherwise dense nanostructured material.…”

Section: Introductionmentioning

confidence: 89%

“…According to Nazarov et al [27], the large concentration of extrinsic non-equilibrium defects in "non-equilibrium" GBs enhances the GB diffusivity by increasing the accumulated free volume and GB excess free energy. The ultrafast diffusivity along some paths in SPD-processed materials is well documented [28,29].…”

Section: Introductionmentioning

confidence: 99%

“…However, more recent studies, from our and other groups [29][30][31][32], have revealed an unexpected feature -a strong heterogeneity of the diffusion rates of general high-angle GBs in ECAPdeformed Cu and Cu-rich alloys [30,31]. In well-annealed polycrystalline metals, the general high-angle GBs represent typically the fastest short-circuit diffusion paths [33].…”

Section: Introductionmentioning

confidence: 99%

“…As this limiting grain size is approached, crack initiation, propagation and fracture result. Using this concept, quantitative guidance can be extracted In addition, this theoretical investigation provides a basis for some of our earlier experimental findings [29][30][31][32]38] and addresses the following questions:…”

Section: Introductionmentioning

confidence: 99%

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Microstructure evolution during severe plastic deformation

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Plasticity and Grain Boundary Diffusion at Small Grain Sizes

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Severe plastic deformation (SPD) processes have attracted considerable attention due to their potential for fabricating large quantities of material with an overall small grain size. [1,2] In the last decade, various SPD processes have been proposed for ultragrain refinement, such as high pressure torsion (HPT), [1] equal channel angular pressing (ECAP) [3] accumulative roll bonding (ARB) [4] or-for achieving the smallest grain sizes for pure metals through SPD-repeated cold rolling (RCR) [5,6] as attractive routes for fabricating bulk nanoand submicron-grained materials. With these approaches, high densities of lattice defects are introduced into the material, which, according to the general view, can then rearrange to attain a minimum energy configuration by forming a submicron cell/sub-grain structure that can evolve to a fine grained microstructure with large fractions of high angle grain boundaries (HAGBs) upon continued straining. It has been observed that materials with fine grain sizes that had been synthesized by such a severe deformation route, exhibit spectacular properties and property combinations, such as, e.g., a very high yield strength and high ductility at the same time, enhanced hydrogen storage capacity and enhanced hydrogen permeation velocity or combinations of high mechanical strength and high electrical conductivity, see, e.g., the recent overview in ref. [7] Along with the modification of the grain structure towards finer grains, the high number of lattice defects that are created led to the postulation of modifications of the grain boundary structure to explain the unusual (mechanical) properties that were observed. In the simplest description, high numberBulk nanostructured-or ultrafine-grained materials are often fabricated by severe plastic deformation to break down the grain size by dislocation accumulation. Underlying the often spectacular property enhancement that forms the basis for a wide range of potential applications is a modification of the volume fraction of the grain boundaries. Yet, along with the property enhancements, several important questions arise concerning the accommodation of external stresses if dislocation-based processes are not longer dominant at small grain sizes. One question concerns so-called ''non-equilibrium'' grain boundaries that have been postulated to form during severe deformation and that might be of importance not only for the property enhancement known already today, but also for spectacular applications in the context of, e.g., gas permeation or fast matter transport for self-repairing structures. This contribution addresses the underlying issues by combining quantitative microstructure analysis at high resolution with grain boundary diffusion measurements.758

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Percolating network of ultrafast transport channels in severely deformed nanocrystalline metals

Cited by 37 publications

References 41 publications

Grain boundaries in ultrafine grained materials processed by severe plastic deformation and related phenomena

Grain boundaries in ultrafine grained materials processed by severe plastic deformation and related phenomena

Microstructure evolution during severe plastic deformation

Plasticity and Grain Boundary Diffusion at Small Grain Sizes

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