Phase Transformations in Pearlitic Steels Induced by Severe Plastic Deformation

2006 ◽  
Vol 114 ◽  
pp. 133-144 ◽  
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.

Stress- and Strain Induced Phase Transformations in Pearlitic Steels

2007 ◽  
Vol 539-543 ◽  
pp. 4681-4686 ◽  
Author(s):  
Julia Ivanisenko ◽  
Witold Łojkowski ◽  
Hans Jorg Fecht
Keyword(s):  
Plastic Deformation ◽  
High Pressure ◽  
Phase Transformations ◽  
Room Temperature ◽  
High Pressures ◽  
High Pressure Torsion ◽  
Carbon Steels ◽  
Coarse Grained ◽  
Cold Plastic Deformation ◽  
Friction Forces

An overview of the mechanically driven phase transformations taking place in nanocrystalline pearlitic steels in conditions of the severe plastic deformation (SPD), i.e. combination of high pressure and strong shear strains will be given. Conditions of the discussed experiments (room temperature and moderate strain rates) exclude any thermal origin of the observed transformations. One of them is strain induced cementite decomposition, which is a well-documented phenomenon taking place at cold plastic deformation of pearlitic steels. We explain this process taking into account friction forces at the interface between the hard cementite and ferrite. Under the high pressures and stresses higher than the ferrite matrix yield stress, the later one behaves like a viscoelastic fluid. The friction at the precipitate/matrix interface leads to two effects. One is to induce high strains on the precipitates. This leads to shift of thermodynamic equilibrium towards dissolution of the cementite. The second is wear of the cementite phase due to friction at the ferrite/cementite interface and mechanically induced drag of carbon atoms by the ferrite. This had been recently confirmed in 3D AP experiments, which demonstrated that the process of cementite decomposition starts with depleting of carbides with carbon and formation of non-stoichiometric cementite. The existing theories of atom drag by moving dislocations (ballistic models) can be regarded as one of the many possible mechanism of wear discussed by the wear theory. In that respect the process can be called athermal, as temperature indirectly influences wear processes but is not their main cause. We observed also another strain driven transformation in nanocrystalline pearlitic steel during room temperature high pressure torsion. This is a stress induced α→γ transformation, which has never been observed at conventional deformation of coarse grained iron and carbon steels. This was concluded to have occurred due to a reverse martensitic transformation.

scholarly journals Plastic Deformation of BaTiO3Ceramics by High-pressure Torsion and Changes in Phase Transformations, Optical and Dielectric Properties

2015 ◽  
Vol 3 (4) ◽  
pp. 216-221 ◽  
Author(s):  
Kaveh Edalati ◽  
Masashi Arimura ◽  
Yoshifumi Ikoma ◽  
Takeshi Daio ◽  
Moriji Miyata ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
High Pressure ◽  
Dielectric Properties ◽  
Phase Transformations ◽  
High Pressure Torsion

scholarly journals DIFFUSIVE AND DISPLACIVE PHASE TRANSFORMATIONS UNDER HIGH PRESSURE TORSION

2019 ◽  
Vol 25 (4) ◽  
pp. 230 ◽  
Author(s):  
Boris Straumal ◽  
Askar Kilmametov ◽  
Andrey Mazilkin ◽  
Olga Kogtenkova ◽  
Brigitte Baretzky ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Plastic Deformation ◽  
Grain Size ◽  
High Pressure ◽  
Phase Composition ◽  
Steady State ◽  
Phase Transformations ◽  
High Pressure Torsion ◽  
Dynamic Equilibrium ◽  
Initial State

<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>

High-pressure torsion of pure cobalt: hcp-fcc phase transformations and twinning during severe plastic deformation

2013 ◽  
Vol 102 (18) ◽  
pp. 181902 ◽  
Author(s):  
Kaveh Edalati ◽  
Shoichi Toh ◽  
Makoto Arita ◽  
Masashi Watanabe ◽  
Zenji Horita
Keyword(s):  
Plastic Deformation ◽  
High Pressure ◽  
Severe Plastic Deformation ◽  
Phase Transformations ◽  
High Pressure Torsion ◽  
Pure Cobalt ◽  
Fcc Phase

TEM Study of Local Disordering: A Structural Phase Change Induced by High-Pressure Torsion

2008 ◽  
Vol 584-586 ◽  
pp. 422-427 ◽  
Author(s):  
Christian Rentenberger ◽  
Clemens Mangler ◽  
Stephan Scheriau ◽  
Reinhard Pippan ◽  
Hans Peter Karnthaler
Keyword(s):  
Plastic Deformation ◽  
High Pressure ◽  
Severe Plastic Deformation ◽  
High Pressure Torsion ◽  
Structural Phase ◽  
Nanocrystalline Structure ◽  
Coarse Grained ◽  
Intermetallic Alloys ◽  
Transmission Electron ◽  
Ordered Intermetallic

Long-range ordered intermetallic alloys with L12 (Ni3Al, Cu3Au) and B2 (FeAl) structures were deformed by high-pressure torsion at room temperature up to high grades of deformation. Transmission electron microscopy shows that disordering caused by the deformation occurs on a very local scale within coarse grains along glide planes (Cu3Au, Ni3Al) and in the form of well defined local regions (Ni3Al, FeAl). The latter leads to a duplex structure consisting of an ordered coarse-grained structure and a disordered nanocrystalline structure. The different mechanisms that can lead to disordering during severe plastic deformation are discussed on the basis of the different ordering energies and on the basis of antiphase boundaries associated with gliding dislocations. The results indicate that in intermetallic alloys the formation of a nanocrystalline structure by severe plastic deformation is facilitated by the loss of order.

GRAIN REFINEMENT AND MICROSTRUCTURE EVOLUTION IN ALUMINUM A2618 ALLOY BY HIGH-PRESSURE TORSION

2016 ◽  
Vol 78 (6-9) ◽  
Author(s):  
Intan Fadhlina Mohamed ◽  
Seungwon Lee ◽  
Kaveh Edalati ◽  
Zenji Horita ◽  
Shahrum Abdullah ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
High Pressure ◽  
Grain Refinement ◽  
Room Temperature ◽  
Rotation Speed ◽  
High Pressure Torsion ◽  
Applied Pressure ◽  
Saturation Level ◽  
Microstructural Refinement ◽  
Average Grain Size

This work presents a study related to the grain refinement of an aluminum A2618 alloy achieved by High-Pressure Torsion (HPT) known as a process of Severe Plastic Deformation (SPD). The HPT is conducted on disks of the alloy under an applied pressure of 6 GPa for 1 and 5 turns with a rotation speed of 1 rpm at room temperature. The HPT processing leads to microstructural refinement with an average grain size of ~250 nm at a saturation level after 5 turns. Gradual increases in hardness are observed from the beginning of straining up to a saturation level. This study thus suggests that hardening due to grain refinement is attained by the HPT processing of the A2618 alloy at room temperature.

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