Phase transformations in a Cu Cr alloy induced by high pressure torsion

<p class="AMSmaintext"><span lang="EN-GB">Severe plastic deformation (SPD) can induce various phase transformations. After a certain strain, the dynamic equilibrium establishes between defects production by an external force and their relaxation (annihilation). The grain size, hardness, phase composition etc. in this steady-state does not depend on the initial state of a material and is, therefore, equifinal. In this review we discuss the competition between precipitation and dissolution of precipitates, amorphization and (nano)crystallization, SPD-induced accelerated mass-transfer, allotropic and martensitic transitions and formation of grain boundary phases.</span></p>

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High-Pressure Torsion Deformation Induced Phase Transformations and Formations: New Material Combinations and Advanced Properties

MATERIALS TRANSACTIONS ◽

10.2320/matertrans.mf201930 ◽

2019 ◽

Vol 60 (7) ◽

pp. 1256-1269 ◽

Cited By ~ 20

Author(s):

Andrea Bachmaier ◽

Reinhard Pippan

Keyword(s):

High Pressure ◽

Phase Transformations ◽

High Pressure Torsion ◽

New Material ◽

Torsion Deformation

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The α→ω and β→ω phase transformations in Ti–Fe alloys under high-pressure torsion

Acta Materialia ◽

10.1016/j.actamat.2017.10.051 ◽

2018 ◽

Vol 144 ◽

pp. 337-351 ◽

Cited By ~ 60

Author(s):

A.R. Kilmametov ◽

Yu. Ivanisenko ◽

A.A. Mazilkin ◽

B.B. Straumal ◽

A.S. Gornakova ◽

...

Keyword(s):

High Pressure ◽

Phase Transformations ◽

High Pressure Torsion ◽

Ω Phase ◽

Fe Alloys

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Phase Transformations in Pearlitic Steels Induced by Severe Plastic Deformation

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.114.133 ◽

2006 ◽

Vol 114 ◽

pp. 133-144 ◽

Cited By ~ 14

Author(s):

Julia Ivanisenko ◽

Ian MacLaren ◽

Xavier Sauvage ◽

Ruslan Valiev ◽

Hans Jorg Fecht

Keyword(s):

Plastic Deformation ◽

High Pressure ◽

Phase Transformations ◽

High Pressure Torsion ◽

Pearlitic Steel ◽

Carbon Steels ◽

Coarse Grained ◽

Cold Plastic Deformation ◽

The Stability ◽

Nanocrystalline Ferrite

The paper presents an overview of a number of unusual phase transformations which take place in pearlitic steels in conditions of the severe deformation, i.e. combination of high pressure and strong shear strain. Strain-induced cementite dissolution is a well-documented phenomenon, which occurs during cold plastic deformation of pearlitic steels. Recently new results which can shed additional light on the mechanisms of this process were obtained thanks to 3DAP and HRTEM investigations of pearlitic steel deformed by high pressure torsion (HPT). It was shown that the process of cementite decomposition starts by carbon depletion from the carbides, which indicates that the deviation of cementite’s chemical composition from the stoichiometric is the main reason for thermodynamic destabilisation of cementite during plastic deformation. Important results were obtained regarding the distribution of released carbon atoms in ferrite. It was experimentally confirmed that carbon segregates to the dislocations and grain boundaries of nanocrystalline ferrite. Another unusual phase transformation taking place in nanocrystalline pearlitic steel during room temperature HPT is a stress induced α→γ transformation, which never occurs during conventional deformation of coarse grained iron and carbon steels. It was concluded that this occurred due to a reverse martensitic transformation. The atomistic mechanism and the thermodynamics of the transformation, as well as issues related to the stability of the reverted austenite will be discussed.

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Omega Phase Formation in Ti–3wt.%Nb Alloy Induced by High-Pressure Torsion

Materials ◽

10.3390/ma14092262 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2262

Author(s):

Anna Korneva ◽

Boris Straumal ◽

Askar Kilmametov ◽

Alena Gornakova ◽

Anna Wierzbicka-Miernik ◽

...

Keyword(s):

Electron Microscopy ◽

High Pressure ◽

Phase Transformations ◽

Grain Refinement ◽

High Pressure Torsion ◽

Β Phase ◽

Ω Phase ◽

Α Phase ◽

Transmission Electron ◽

Different Temperatures

It is well known that severe plastic deformation not only leads to strong grain refinement and material strengthening but also can drive phase transformations. A study of the fundamentals of α → ω phase transformations induced by high-pressure torsion (HPT) in Ti–Nb-based alloys is presented in the current work. Before HPT, a Ti–3wt.%Nb alloy was annealed at two different temperatures in order to obtain the α-phase state with different amounts of niobium. X-ray diffraction analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied for the characterisation of phase transitions and evolution of the microstructure. A small amount of the β-phase was found in the initial states, which completely transformed into the ω-phase during the HPT process. During HPT, strong grain refinement in the α-phase took place, as did partial transformation of the α- into the ω-phase. Therefore, two kinds of ω-phase, each with different chemical composition, were obtained after HPT. The first one was formed from the β-phase, enriched in Nb, and the second one from the α-phase. It was also found that the transformation of the α-phase into the ω-phase depended on the Nb concentration in the α-Ti phase. The less Nb there was in the α-phase, the more of the α-phase was transformed into the ω-phase.

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