Phase transitions induced by severe plastic deformation: steady-state and equifinality

Straumal, Boris B.; Kilmametov, Askar; Ivanisenko, Yulia; Мазилкин, А. А.; Kogtenkova, O. A.; Kurmanaeva, Lilia; Korneva, Anna; Zięba, P.; Baretzky, B.

doi:10.3139/146.111215

Cited by 87 publications

(48 citation statements)

References 76 publications

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“…The processes of dislocation generation, recovery and the interaction of dislocations with precipitation products and the possibility of particle breakage are areas requiring further exploration. Nevertheless, the very weak evolution of hardness upon HPT processing between ½ and 10 turns appears to be due to a steady-state dislocation generation in work hardening and the annihilation or recovery of dislocations as proposed also in another report [75].…”

Section: Hardness Evolutionmentioning

confidence: 55%

Texture and microhardness of Mg-Rare Earth (Nd and Ce) alloys processed by high-pressure torsion

Bourezg

Azzeddine

Baudin

et al. 2018

Materials Science and Engineering: A

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The influence of high-pressure torsion (HPT) processing on the texture and microhardness of two binary Mg-RE (RE=Nd and Ce) alloys was investigated using X-ray diffraction and Vickers microhardness measurements. Disks cut from the alloys were processed by HPT at room temperature for up to 10 turns. The precipitation products of both alloys were identified using synchrotron radiation. The results show that both alloys exhibit a weak basal texture where the c-axis of most grains is shifted 15° from the shear direction. An Mg-1.44Ce (wt. %) alloy showed a continuous decrease in the texture strength which may be due to the effect of second precipitation phases (Mg 17 Ce 2 and MgCe 2). The microhardness of both alloys increased significantly with increasing HPT turns but levelled-off beyond about one HPT turn. Maximum values of ~65 and ~96 Hv were achieved which are significantly higher than the hardness of the undeformed Mg-Ce and Mg-Nd alloys.

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Section: Hardness Evolutionmentioning

confidence: 55%

Texture and microhardness of Mg-Rare Earth (Nd and Ce) alloys processed by high-pressure torsion

Bourezg

Azzeddine

Baudin

et al. 2018

Materials Science and Engineering: A

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“…54)) and its independence of the loading history is confirmed experimentally in Ref. 56) by observed incompletion of various PTs, and by the existence of the stationary state independent of the processing history (equifinality). In turn, existence of the stationary solution with incomplete PT means that p d ¾ < p r ¾ for a given PT and that PT is strongly affected by plastic strain.…”

Section: Thermodynamically Consistent Kinetics Of Plastic Strain Indumentioning

confidence: 62%

High-Pressure Phase Transformations under Severe Plastic Deformation by Torsion in Rotational Anvils

Levitas

2019

Mater. Trans.

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Numerous experiments have documented that combination of severe plastic deformation and high mean pressure during high-pressure torsion in rotational metallic, ceramic, or diamond anvils produces various important mechanochemical effects. We will focus here on four of these: plastic deformation (a) significantly reduces pressure for initiation and completion of phase transformations (PTs), (b) leads to discovery of hidden metastable phases and compounds, (c) reduces PT pressure hysteresis, and (d) substitutes a reversible PT with irreversible PT. The goal of this review is to summarize our current understanding of the underlying phenomena based on multiscale atomistic and continuum theories and computational modeling. Recent atomistic simulations provide conditions for initiation of PTs in a defect-free lattice as a function of the general stress tensor. These conditions (a) allow one to determine stress states that significantly decrease the transformation pressure and (b) determine whether the given phase can, in principle, be preserved at ambient pressure. Nanoscale mechanisms of phase nucleation at plastic-strain-induced defects are studied analytically and by utilizing advanced phase field theory and simulations. It is demonstrated that the concentration of all components of the stress tensor near the tip of the dislocation pileup may decrease nucleation pressure by a factor of ten or more. These results are incorporated into the microscale analytical kinetic equation for strain-induced PTs. The kinetic equation is part of a macroscale geometrically-nonlinear model for combined plastic flow and PT. This model is used for finite-element simulations of plastic deformations and PT in a sample under torsion in a rotational anvil device. Numerous experimentally-observed phenomena are reproduced, and new effects are predicted and then confirmed experimentally. Combination of the results on all four scales suggests novel synthetic routes for new or known high-pressure phases (HPPs), experimental characterization of strain-induced PTs under high-pressure during torsion under elevated pressure.

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“…The method in a revised form of shear or rotational diamond anvil cell was successfully employed for in situ examination of phase transformation . The method still receives significant attention in the SPD community to control the phase transformations in metals and alloys . Our studies on phase transformation of oxides by HPT processing reveal three main findings.…”

Section: Recent Findings On Hpt Processing Of Oxidesmentioning

confidence: 99%

“…In 1988, Ruslan Z. Valiev and his co‐workers in Russia employed the Bridgman method to produce ultrafine‐grained (UFG) metals and alloys with large density of lattice defects and enhanced properties . Since 1988 and particularly within this century, many researchers employed the HPT method or other novel SPD techniques to produce UFG metals and alloys with functional properties and specific phases …”

Section: Introductionmentioning

confidence: 99%

Review on Recent Advancements in Severe Plastic Deformation of Oxides by High‐Pressure Torsion (HPT)

Edalati

2018

Adv Eng Mater

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Severe plastic deformation (SPD) of oxides has been of interest in mineralogy and geology for many decades, but oxides have ionic or covalent bonds with brittle nature and can hardly be deformed at ambient temperature. SPD processing of oxides is first realized in 1930s, when Percy W. Bridgman introduce the principles of high-pressure torsion (HPT) method. Although the method is widely used nowadays to produce ultrafine-grained (UFG) metals, the application of method for SPD processing of oxides is quite limited. This article reviews some of the recent publications on the application of HPT method to oxide ceramics () and summarizes their major findings: powder compaction and partial consolidation, nanograin formation, formation of different kinds of lattice defects such as dislocations and oxygen vacancies, strain and grain size dependence of phase transformations, and improvement of functional properties such as bandgap narrowing, photoluminescence, photocatalytic activity, and dielectricity. Early Studies on HPT Processing of OxidesAs mentioned earlier, SPD processing of oxides has been of interest for many decades in mineralogy and geology. Boeker is

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Phase transitions induced by severe plastic deformation: steady-state and equifinality

Cited by 87 publications

References 76 publications

Texture and microhardness of Mg-Rare Earth (Nd and Ce) alloys processed by high-pressure torsion

Texture and microhardness of Mg-Rare Earth (Nd and Ce) alloys processed by high-pressure torsion

High-Pressure Phase Transformations under Severe Plastic Deformation by Torsion in Rotational Anvils

Review on Recent Advancements in Severe Plastic Deformation of Oxides by High‐Pressure Torsion (HPT)

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