Significance of strain rate in severe plastic deformation on steady-state microstructure and strength

Edalati, Kaveh; Wang, Qing; Enikeev, Nariman A.; Peters, Laura-Jean; Zehetbauer, M.; Schafler, Erhard

doi:10.1016/j.msea.2022.144231

Cited by 14 publications

(2 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1(c) and 1(d) (bright-field and dark-field images, respectively). It is clearly seen that after HPT, the grain size, as in many other studies, 4,5,10) decreased by 23 orders of magnitude. No visual traces of martensite plates are left either.…”

Section: Hpt Of ¡¤ Martensitesupporting

confidence: 84%

Review - Phase Transitions in Ti Alloys Driven by the High Pressure Torsion

et al. 2023

View full text Add to dashboard Cite

The high pressure torsion (HPT) of various binary Ti alloys with ¢-stabilizers (Fe, Co, Ni, Mo, Nb) was studied. Before HPT, the samples were annealed and contained (i) pure ¢-phase, (ii) ¡+¢ mixture with different portion of phases, (iii) ¡A or ¡AA martensites, (iv) the mixture of ¡-Ti and respective intermetallic phase. The microstructure of Ti alloys before and after HPT was studied by scanning and transmission electron microscopy (also high resolution one), X-rays diffraction (including the high-temperature in situ one), differential scanning calorimetry, atomic probe tomography, synchrotron irradiation. During HPT the (usual) strong grain refinement took place. Also, it was observed that HPT can lead to various phase transitions in the Ti alloys. In particular, the metastable high-pressure ½-phase and ¡A martensite can form. The composition of phases (similar to their grain size) reached the steady-state value after about 1.5 plunger revolutions. In some cases, the equifinality of the HPT-driven phase transitions was observed. Equifinality means that the composition and portion of phases after HPT do not depend on the composition and portion of phases before HPT.The HPT-driven phase transitions can be martensitic (i.e. without or almost without mass transfer) or diffusional (i.e. with mass transfer). In case of martensitic ¢-to-½ or ¡-to-½ phase transitions, the certain orientation relations between ¢ and ½ or ¡ and ½ phases were observed. The thermal stability of the ½-phase obtained by HPT has been studied by the in-situ X-rays diffraction at high temperatures. The ½-phase in the HPT-treated Ti alloys with ¢-stabilizers can remain in the samples up to 500600°C. It is much higher than in pure titanium (³180°C). Thus, the HPT-driven phase transitions open the new way for tailoring of grain size and phase composition of Ti-based alloys. In turn, it gives the new instrument in hands of engineers to improvement of the technologically important properties of Ti-based alloys. It is especially important for the medical application like the teeth or bone prosthesis.

show abstract

Section: Hpt Of ¡¤ Martensitesupporting

confidence: 84%

Review - Phase Transitions in Ti Alloys Driven by the High Pressure Torsion

et al. 2023

View full text Add to dashboard Cite

show abstract

“…179) Since both rates of grain refinement and dynamic recrystallization are proportional to the strain rate, the steady-state grain size is independent of the strain rate. 179) Making dual-phase alloys and composites can result in more significant grain refinement, provided that the strain is high enough to mix phases or distribute nanoparticles in the matrix. 135) These nanoparticles pin grain boundaries and dislocations.…”

Section: Grain Refinementmentioning

confidence: 99%

Severe Plastic Deformation of Light Metals (Magnesium, Aluminum and Titanium) and Alloys by High-Pressure Torsion: Review of Fundamentals and Mechanical/Functional Properties

Edalati

2024

Mater. Trans.

Self Cite

View full text Add to dashboard Cite

Light metals and alloys based on magnesium, aluminum, and titanium are of significance in daily life and industrial applications due to their low density and superior mechanical and functional properties. The formation of nanostructures and ultrafine grains can further improve the properties of these materials. High-pressure torsion (HPT), as a severe plastic deformation (SPD) method, is one of the most effective processes for nanostructuring these materials. Various modifications of HPT such as conventional HPT with discs, HPT with rings, and continuous HPT with strips and wires are currently applied to light metals and their alloys, composites, intermetallics, and metallic glasses. The HPT processing of these materials is effective for grain refinement, hardening through the Hall-Petch mechanism, lattice defect generation, phase transformations, and solid-state reactions through fast diffusion with reasonable time/thermal stability. This article after discussing these fundamental issues, reviews some mechanical and functional properties of nanostructured lightweight materials such as tensile, compression, and bending properties, superplasticity including room-temperature superplasticity, wear resistance, electrical conductivity, superconductivity, biocompatibility, hydrogen production, and hydrogen storage.

show abstract

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

Renk,

Hohenwarter,

Edalati

et al. 2024

Adv Eng Mater

View full text Add to dashboard Cite

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.

show abstract

Significance of strain rate in severe plastic deformation on steady-state microstructure and strength

Cited by 14 publications

References 39 publications

Review - Phase Transitions in Ti Alloys Driven by the High Pressure Torsion

Review - Phase Transitions in Ti Alloys Driven by the High Pressure Torsion

Severe Plastic Deformation of Light Metals (Magnesium, Aluminum and Titanium) and Alloys by High-Pressure Torsion: Review of Fundamentals and Mechanical/Functional Properties

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

Contact Info

Product

Resources

About