Generation of extreme grain aspect ratios in severely deformed tantalum at elevated temperatures

Renk, Oliver; Ghosh, Pradipta; Pippan, Reinhard

doi:10.1016/j.scriptamat.2017.04.024

Cited by 26 publications

(26 citation statements)

References 27 publications

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“…While the major grain axis increased by almost a factor of four increasing the deformation temperature to 673 K, the minor axis became only twice as large. 80) Accordingly, the aspect ratio strongly increased with deformation temperature, reaching almost values of ten for deformation temperatures of 673 K. This is in contrast to the common observations that an increase of the deformation temperature causes a reduction of the aspect ratio. 25,37,50,81) Only for temperatures being larger than 673 K, the aspect ratio of the tantalum samples reduced again.…”

Section: Effect Of Deformation Temperature On the Saturationmentioning

confidence: 58%

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Saturation of Grain Refinement during Severe Plastic Deformation of Single Phase Materials: Reconsiderations, Current Status and Open Questions

Renk

Pippan

2019

Mater. Trans.

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Grain refinement of materials by severe plastic deformation, investigation and understanding of their properties and phenomena has been a subject of intensive research over the last three decades. Along with the invention and development of these processes it has been recognized, that grain refinement is not indefinite but stagnates for single phase materials. Accordingly, the minimum grain sizes achievable are in the range between 50 and 500 nm. Motivated to find ways to overcome these limitations, effort has been made to understand the reasons behind. Various processes were suggested to cause saturation of grain fragmentation. While all of these assumptions and models were not based on direct observations, recently in-situ approaches allowed significant progress in understanding microstructural evolution and the principle restoration processes during severe straining. It is the aim of this work to recap important earlier findings, reconsider proposed models and to present our current understanding of the processes limiting grain refinement upon severe straining. Further it will be discussed, that similar processes generally occur during deformation of such fine scaled materials. They do not only govern saturation of grain refinement during severe deformation but more important also the mechanical response and performance of these materials. This motivates an in-depth understanding and therefore open questions as well as discrepancies between various experiments will be deliberately highlighted to stimulate further research and thus progress within this area.

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Section: Effect Of Deformation Temperature On the Saturationmentioning

confidence: 58%

“…This is in line with an earlier study on tantalum having slightly lower purity (99.95%). 80) Interestingly, up to a certain deformation temperature the dimensions of the major grain axis increased more pronounced than the ones of the minor grain axis, compare Fig. 6.…”

Section: Effect Of Deformation Temperature On the Saturationmentioning

confidence: 83%

Saturation of Grain Refinement during Severe Plastic Deformation of Single Phase Materials: Reconsiderations, Current Status and Open Questions

Renk

Pippan

2019

Mater. Trans.

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“…Materials processed by SPD are characterized by high dislocation densities, 3) "non-equilibrium" grain boundaries 11) and high vacancy concentrations. 51,52) All these defects may influence the atomic mobility: dislocations could drag solutes 53) or act as diffusion pipes; 54) GBs are also fast diffusion paths 12) and could drag solute when they move during the deformation, 23,24,42) and at last, strain induced vacancies will directly enhance the atomic diffusion. 27) These respective contributions have been reviewed in Ref.…”

Section: Fundamental Mechanismsmentioning

confidence: 99%

“…This view is supported by recent work on strain induced grain boundary motion which is major phenomena occurring during SPD. 23,24) Thus, like during classical grain growth, 25) the interaction between solutes (or impurities) and GBs might significantly modify their energy and mobility and thus the microstructure resulting from SPD. This effect is of course more pronounced in case of GB segregations which is a frequent feature in metallic alloys processed by SPD as it will be shown in the following section.…”

Section: Introductionmentioning

confidence: 99%

Strain Induced Segregations in Severely Deformed Materials

2019

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Severely deformed materials intrinsically contain a large density of crystalline defects like dislocations or boundaries. The interactions between solute atoms or impurities with these defects play a key role in the grain refinement mechanisms as they affect dynamic recovery. This short review manuscript focusses on grain boundary segregations resulting from severe plastic deformation. The important contribution of atom probe tomography for the quantitative characterization of such segregations in various metallic alloys is at first highlighted. Then, a special emphasis is given on the physical mechanisms leading to strain induced segregations and on the connection that is sometimes observed with dynamic precipitation during severe plastic deformation. The last section is devoted to the influence of such grain boundary segregations in ultrafine grained alloys on the mechanical properties and on the thermal stability. [

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“…For tantalum components, investigations regarding the effect of rolling, high-pressure torsion and equal-channel angular pressing on the microstructural refinement have already been reported [26][27][28][29][30]. In particular, ultrafine and nanostructured tantalum components can be produced by applying severe plastic deformation steps to a conventional coarse-grained structure, achieving nanometre-size grains [28,31].…”

Section: Introductionmentioning

confidence: 99%

Grain refinement in an unalloyed tantalum structure by combining Wire+Arc additive manufacturing and vertical cold rolling

Marinelli

Martina

Ganguly

et al. 2020

Additive Manufacturing

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Components manufactured via Wire + Arc Additive Manufacturing are usually characterised by large columnar grains. This can be mitigated by introducing in-process cold-rolling; in fact, the associated local plastic deformation leads to a reduction of distortion and residual stresses, and to microstructural refinement. In this research, interpass rolling was applied with a load of 50 kN to a tantalum linear structure to assess its effectiveness in changing the grain structure from columnar to equiaxed, as well as in refining the grain size. An average grain size of 650 µm has been obtained after five cycles of inter-pass rolling and deposition. When the deformed layer was reheated during the subsequent deposition, recrystallisation occurred, leading to the growth of new strain-free finer equiaxed grains. The depth of the refined region has been characterised and correlated to the hardness profile developed after rolling. A reduction of porosity was also registered. Furthermore, a random texture was formed after rolling, which should result in isotropic mechanical properties. Wire + Arc Additive Manufacturing process demonstrated the ability to deposit sound refractory metal components and the possibility to improve the microstructure when coupled with cold inter-pass rolling.

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Generation of extreme grain aspect ratios in severely deformed tantalum at elevated temperatures

Cited by 26 publications

References 27 publications

Saturation of Grain Refinement during Severe Plastic Deformation of Single Phase Materials: Reconsiderations, Current Status and Open Questions

Saturation of Grain Refinement during Severe Plastic Deformation of Single Phase Materials: Reconsiderations, Current Status and Open Questions

Strain Induced Segregations in Severely Deformed Materials

Grain refinement in an unalloyed tantalum structure by combining Wire+Arc additive manufacturing and vertical cold rolling

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