How grain boundary characteristics influence plasticity close to and above the critical temperature of ultra-fine grained bcc Ta2.5W

Kappacher, Johann; Renk, Oliver; Kiener, Daniel; Clemens, Helmut; Maier–Kiener, Verena

doi:10.1016/j.actamat.2021.117110

Cited by 13 publications

(1 citation statement)

References 77 publications

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“…A straight forward comparison of different lamellae spacings by micro compression experiments emphasized the importance of dislocation confinement for strengthening [45]. This is further supported, when considering that deformation mechanisms in these nanostructures rely on emission and accommodation of dislocation within the interfaces [67][68][69], followed by movement of half loops through the lamellar channel in elongated grains. The latter is known as confined layer slip and is a well-studied feature in multilayers [17,[70][71][72][73][74][75] causing an exceptional strain hardening capacity [76] and therefore ductility [38] in such architectures.…”

Section: Strengthening Mechanisms In Lamellar Architecturesmentioning

confidence: 65%

SPD Deformation of Pearlitic, Bainitic and Martensitic Steels

et al. 2023

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The deformation behavior of nearly fully pearlitic, bainitic and martensitic steels during severe plastic deformation is summarized in this paper. Despite their significantly different yield stresses and their microstructures, their hardening behavior during SPD is similar. Due to the enormous hardening capacity the SPD deformation is limited by the strength of the tool materials. The microstructure at the obtainable limit of strain are quite similar, which is a nanocrystalline structure in the order of 10 nm, dependent on the obtainable strain. The nanograins are partially supersaturated with carbon and the grain boundaries are stabilized by carbon. Another characteristic feature is the anisotropy in grain shape which results in an anisotropy of strength, ductility and fracture toughness. The results are important for the development of ultra-strong materials and essential for this type of steels which are frequently used for application where the behavior under rolling contact and sliding contact is important.

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Section: Strengthening Mechanisms In Lamellar Architecturesmentioning

confidence: 65%

SPD Deformation of Pearlitic, Bainitic and Martensitic Steels

et al. 2023

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Saturation of Grain Fragmentation upon Severe Plastic Deformation: Fact or Fiction?

Renk,

Hohenwarter,

Edalati

et al. 2024

Adv Eng Mater

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There has been general agreement that grain refinement upon severe plastic deformation (SPD) saturates at equivalent strains of 10–20, as a dynamic equilibrium between refinement and coarsening is established. Meanwhile, few reports question such steady state, but suggest another strain hardening regime might be entered for strains >1000. So far, neither an in‐depth analysis nor a general theory for such ultra‐SPD strain hardening has been established. The present work provides clear evidence for additional strain hardening at ultra‐severe strains. Although at this stage the strain hardening rate is awfully weak (≈0.03 MPa), it manifests in noticeable grain refinement and hardness increase. Texture and the existence of subgrains still support dislocation‐based plasticity. Specimens deformed to ultra‐severe strains possess improved thermal stability. Although an unambiguous conclusion regarding the origin of the ultra‐SPD strain hardening is currently not possible, the potential mechanisms are being discussed. While continuous impurity uptake from the anvils could explain the hardening and improved thermal stability, estimation of grain boundary migration rates suggests that a slight but continuous net refinement is also plausible. Together with structural transformations of grain boundaries, this offers an alternative, intrinsic source for ultra‐SPD hardening. It is hoped that this thought‐provoking conclusion stimulates further research into this subject.

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Interface Engineering at the Nanoscale: Synthesis of Low‐Energy Boundaries

Kapp,

Eckert,

Renk

2024

Adv Eng Mater

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The low toughness and structural stability of nanostructured materials are strongly related to the numerous grain boundaries and interfaces. Among other design stratgies, the use of low‐energy boundaries has turned out to provide the most comprehensive improvement of the property spectrum targeting on ductility, toughness, as well as thermal and microstructural stability upon mechanical loading. Cyclic high‐pressure torsion (CHPT) is one prosperous technique to synthesize low‐angle boundaries (LAGB) at the nanoscale, enabling the production of high‐strength materials. It is presented here with an in‐depth analysis of the structural evolution focusing on the effect of different strain amplitudes and accumulated strains as well as crystal structure to understand how these parameters need to be adjusted to optimize the fraction of LAGBs. Different than expected from classical fatigue testing, the crystal structure seems to play a minor role for the cell structure evolution at comparably large strain amplitudes. It is, therefore, a strong asset that CHPT is feasible to produce nanostructures LAGB boundaries in both FCC and BCC structures. Furthermore, by optimizing the geometry of the anvils, it enables homogenous structural sizes in the entire sample as in contrast to other techniques the strain gradient impact on LAGB formation can be overcome.

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How grain boundary characteristics influence plasticity close to and above the critical temperature of ultra-fine grained bcc Ta2.5W

Cited by 13 publications

References 77 publications

SPD Deformation of Pearlitic, Bainitic and Martensitic Steels

SPD Deformation of Pearlitic, Bainitic and Martensitic Steels

Saturation of Grain Fragmentation upon Severe Plastic Deformation: Fact or Fiction?

Interface Engineering at the Nanoscale: Synthesis of Low‐Energy Boundaries

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