Nonequilibrium grain boundaries in bulk nanostructured metals and their recovery under the influences of heating and cyclic deformation. Review

Назаров, А. А.

doi:10.22226/2410-3535-2018-3-372-381

Cited by 30 publications

(9 citation statements)

References 30 publications

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“…30,31) For detail on non-equilibrium grain boundaries, please see the recent review by Nazarov. 32) Non-equilibrium grain boundaries, or alternatively grain boundaries of nonequilibrium configuration, 33) may impact the corrosion behavior of severely deformed materials. Indeed, there are cases in which corrosion behavior of SPD materials cannot be predicted by extrapolating from the conventional processing regime where the microstructure typically consists of dislocation substructures.…”

Section: Introductionmentioning

confidence: 99%

Corrosion Behavior of Severely Deformed Pure and Single-Phase Materials

et al. 2019

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The significant and complex effect of plastic deformation on corrosion behavior involves changes in not only dislocation density but also other metallurgical factors such as grain size, texture, chemical inhomogeneity, phase transformation and residual stress. With the advent of severe plastic deformation (SPD), the effect of plastic deformation on corrosion in the ultrahigh strain range is becoming an important issue. However, our understanding of corrosion properties of SPD materials lags far behind than that of their other properties, e.g. their mechanical properties. In this review, the role of dislocations and grain boundaries generated by SPD was highlighted in pure metals and single-phase materials, where plastic deformation and grain refinement proceed mainly by dislocation activity. Accordingly, the complicated effect of chemical inhomogeneity arising from impurity segregation and precipitation was excluded from discussion, while other implicit effects were included. It is essential to elucidate the effect of so-called ultrafine-grained (UFG) structures which develop progressively to a saturation over a very wide strain range. Unfortunately, the literature mainly compares the corrosion behavior of UFG and coarse-grained (CG) materials, and the degree of perfection of UFG formation and the resultant effects on corrosion vary between studies. The limited number of studies that examines corrosion behavior systematically over a wide strain range suggests that, in most cases, the effect of plastic deformation on corrosion extends into the SPD region gradually, with no anomalous change. That is, SPD improves the corrosion resistance to further degree in a passive environment, whereas it increases the dissolution rate in a non-passive environment. However, several works reported an abrupt change in corrosion resistance, which could be attributed to UFG formation. A marked improvement is observed in FeCr alloys, where passivation becomes more protective owing to UFG formation induced by SPD. In severely deformed materials, structural alterations in dislocations and grain boundaries have a very high impact on the corrosion kinetics because of their closely spaced configuration.

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Section: Introductionmentioning

confidence: 99%

Corrosion Behavior of Severely Deformed Pure and Single-Phase Materials

et al. 2019

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“…Accordingly, qualitative changes in energy dissipation were observed during the cyclic loading of the UFG and CG Ti-45Nb alloys. It has been proved elsewhere [ 51 , 52 ] that CG and UFG aluminum alloys subjected to dynamic compression are characterized by different energy dissipation, which is associated with their different grain sizes and defect micro-structures.…”

Section: Resultsmentioning

confidence: 99%

Characteristic Features of Ultrafine-Grained Ti-45 wt.% Nb Alloy under High Cycle Fatigue

et al. 2021

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The paper presents the results of fatigue-testing ultrafine-grained and coarse-grained Ti-45 wt.% Nb alloy samples under very high cycle fatigue (gigacycle regime), with the stress ratio R = −1. The ultrafine-grained (UFG) structure in the investigated alloy was formed by the two-stage SPD method, which included multidirectional forging (abc–forging) and multipass rolling in grooved rollers, with further recrystallization annealing. The UFG structure of the Ti-45 wt.% Nb alloy samples increased the fatigue limit under the high-cycle fatigue conditions up to 1.5 times compared with that of the coarse-grained (CG) samples. The infrared thermography method was applied to investigate the evolution of temperature fields in the samples under cyclic loading. Based on numerical morphology analysis, the scale invariance (the Hurst exponent) and qualitative differences for UFG and CG structures were determined. The latter resulted from the initiation and propagation of fatigue cracks in both ultra-fine grained and coarse-grained alloy samples under very high-cycle fatigue loading.

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“…"Relaxing" general grain boundaries into lower energy states can be achieved through various mechanisms. Conventional thermally activated relaxation mechanisms include the annealing out of excess boundary dislocations, rearranging atoms in the grainboundary region to effect a more uniform free volume distribution, 48,125 the formation of facets on specific low-energy planes, or the generation of local structural units with lower energies separated by junctions. Dissociation of grain boundaries through interaction with partial dislocations provides an alternative mechanism for their relaxation.…”

Section: Promoting Low-energy Grain-boundary Crystallographiesmentioning

confidence: 99%

Stability of nanocrystalline metals: The role of grain-boundary chemistry and structure

Schuh

2021

MRS Bulletin

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Nanocrystalline metals are transitioning from laboratory curiosities to engineering materials, in large part due to advances in improving their stability, making their exceptional properties more predictable and accessible. Nanoscale grains typically have a very strong innate tendency to coarsen, but the grain-boundary structure can be designed and tuned to lower its excess energy, reducing both the driving force for coarsening and the grain-boundary mobility. This article reviews two major strategies for achieving low-energy grain boundaries in nanocrystalline structures. First, grain-boundary alloying is discussed, including grainboundary segregation and its energetic competition with the formation of second phases; with sufficient grain-boundary segregation tendency it is possible to stabilize nanostructures to high temperatures. Second, methods of achieving low-energy crystallographic grainboundary structures are discussed, including the formation of nanotwinned structures and relaxing grain boundaries into low-energy structures through their interactions with partial dislocations. Both of these strategies have led to effective and implementable stable nanocrystalline materials, and point to many directions for future advancements.

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Nonequilibrium grain boundaries in bulk nanostructured metals and their recovery under the influences of heating and cyclic deformation. Review

Cited by 30 publications

References 30 publications

Corrosion Behavior of Severely Deformed Pure and Single-Phase Materials

Corrosion Behavior of Severely Deformed Pure and Single-Phase Materials

Characteristic Features of Ultrafine-Grained Ti-45 wt.% Nb Alloy under High Cycle Fatigue

Stability of nanocrystalline metals: The role of grain-boundary chemistry and structure

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