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Hug E.,CNRS Crystallography and Material Science Laboratory | Prasath Babu R.,University of Manchester | Prasath Babu R.,CNRS Material Physics Group | Monnet I.,French Atomic Energy Commission | And 7 more authors.
Applied Surface Science | Year: 2017

The influence of grain size and irradiation defects on the mechanical behavior and the corrosion resistance of a 316 stainless steel have been investigated. Nanostructured samples were obtained by severe plastic deformation using high pressure torsion. Both coarse grain and nanostructured samples were irradiated with 10 MeV 56Fe5+ ions. Microstructures were characterized using transmission electron microscopy and atom probe tomography. Surface mechanical properties were evaluated thanks to hardness measurements and the corrosion resistance was studied in chloride environment. Nanostructuration by high pressure torsion followed by annealing leads to enrichment in chromium at grain boundaries. However, irradiation of nanostructured samples implies a chromium depletion of the same order than depicted in coarse grain specimens but without metallurgical damage like segregated dislocation loops or clusters. Potentiodynamic polarization tests highlight a definitive deterioration of the corrosion resistance of coarse grain steel with irradiation. Downsizing the grain to a few hundred of nanometers enhances the corrosion resistance of irradiated samples, despite the fact that the hardness of nanocrystalline austenitic steel is only weakly affected by irradiation. These new experimental results are discussed in the basis of couplings between mechanical and electrical properties of the passivated layer thanks to impedance spectroscopy measurements, hardness properties of the surfaces and local microstructure evolutions. © 2016 Elsevier B.V.


Zinovev A.V.,Belgian Institute for Nuclear Sciences | Zinovev A.V.,Catholic University of Leuven | Bapanina M.G.,RAS Institute for Metals Superplasticity Problems | Babicheva R.I.,Nanyang Technological University | And 3 more authors.
Physics of Metals and Metallography | Year: 2017

The influence of the temperature and sort of alloying element on the deformation of the nanocrystalline (NC) binary Al alloys with segregation of 10.2 at % Ti, Co, or Mg over grain boundaries has been studied using the molecular dynamics. The deformation behavior of the materials has been studied in detail by the simulation of the shear deformation of various Al bicrystals with the grain-boundary segregation of impurity atoms, namely, Ti, Co, or Mg. The deformation of bicrystals with different grain orientation has been studied. It has been found that Co introduction into grain boundaries of NC Al has a strengthening effect due to the deceleration of the grain-boundary migration (GBM) and difficulty in the grain-boundary sliding (GBS). The Mg segregation at the boundaries greatly impedes the GBM, but stimulates the development of the GBS. In the NC alloy of Al–Ti, the GBM occurs actively, and the flow-stress values are close to the values characteristic of pure Al. © 2017, Pleiades Publishing, Ltd.


Valiev R.R.,Institute of Physics of Advanced Materials | Smirnov I.V.,Saint Petersburg State University
IOP Conference Series: Materials Science and Engineering | Year: 2014

Cycling of the compression pressure during high pressure torsion (HPT) of the titanium Ti-6Al-4V alloy significantly improves the grain refinement process, and also results in a more uniform microstructure along the sample diameter. © Published under licence by IOP Publishing Ltd.


Zrnik J.,Comtes Fht | Lapovok R.,Monash University | Raab G.I.,Institute of Physics of Advanced Materials
IOP Conference Series: Materials Science and Engineering | Year: 2014

The article focuses on the severe plastic deformation (SPD) of low carbon steel AISI 1010 performed at increased temperature. The grain refinement of ferrite structure is monitored and described with respect to different initial steel structure modified by thermal and thermomechanical (TM) treatment (TM) prior severe plastic deformation. The refinement of coarse initial ferrite structure with grain size in range of 30-50 gm resulted from solutioning was conducted then in two steps. Preliminary structure refinement has been achieved due to multistep open die forging process and quite uniform ferrite structure with grain size of the order of gm was obtained. The further grain refinement steel structure was then accomplished during warm Equal Channel Angular Pressing (ECAP φ 120°) at 300°C, introducing different strain in range of ef 2.6 -4. The change of microstructure in dependence of the effective strain was evaluated by SEM and TEM study of thin foils. The high straining of steel resulted in extensive deformation of ferrite grains and formation of mixture of submicron grains structure in banded deformed structure with dense dislocation network and subgrains. The dynamic polygonization process, due to increased ECAP temperature, modified the submicrocrystalline structure formation. There was only indistinctive difference observed in structure refinement when considering different initial structure of steel. The tensile behaviour was characterized by strength increase followed by softening. None work hardening phenomenon appeared at tensile deformation of deformed bars. © Published under licence by IOP Publishing Ltd.


Zhu Y.,North Carolina State University | Valiev R.Z.,Institute of Physics of Advanced Materials | Langdon T.G.,University of Southern California | Tsuji N.,Kyoto University | Lu K.,CAS Shenyang Institute of Metal Research
MRS Bulletin | Year: 2010

Plastic deformation can effectively produce nanostructured metals and alloys in bulk or surface-layer forms that are suitable for practical structural or functional applications. Such nanostructured materials are porosity-free and contamination-free, and therefore they are ideal for studying fundamental mechanisms and mechanical properties. In this article, we first give an overview of the principles of grain refinement by plastic deformation and an introduction to the reported processing techniques. Then the four most-developed and promising techniques will be described in detail: equal-channel angular pressing, high-pressure torsion, accumulative roll bonding for bulk nanostructured metals, and surface mechanical attrition treatment for nanostructured surface layers.


Zrnik J.,Comtes Fht | Dobatkin S.V.,RAS Institute of Metallurgy | Raab G.I.,Institute of Physics of Advanced Materials | Kraus L.,Comtes Fht
Kovove Materialy | Year: 2013

The present work deals with grain refinement of medium carbon steel AISI 1045 (0.45 wt.% C) having different initial ferrite-pearlite microstructure resulted from thermal and thermomechanical (TM) treatment. The purpose of prior TM steel processing was to refine grains of ferrite phase and to modify coarse lamellae pearlite structure. The final grain refinement of steel structure was then accomplished during warm Equal Channel Angular Pressing (ECAP) deformation at 400°C. Employment of this processing route, in dependence of the applied effective strain εef, resulted in extensive deformation of ferrite grains and cementite lamellae fragmentation. When applying higher shear stress, the mixed structure of subgrains and ultrafine grains was formed within ferrite phase, regardless the initial steel modification. In pearlite grains modification of cementite lamellae due to shearing, bending, twisting and breaking was found efficient as straining increased. Processes of dynamic polygonization and recrystallization in deformed structure also contributed to submicrocrystalline grains structure formation in intensively deformed structure. Comparing results of coarse lamellae cementite spheroidization it was then more efficient when prior TM treatment of steel was introduced. The tensile deformation results confirmed the strength increase, however, deformation behaviour and strain hardening, generally for different initial structural conditions of steel, showed diversity across deformed bars.


Zrnik J.,Comtes Fht | Dobatkin S.,Russian Academy of Sciences | Raab G.,Institute of Physics of Advanced Materials | Kraus L.,Comtes Fht | Fujda M.,Technical University of Košice
TMS Annual Meeting | Year: 2011

The present work, likewise, deals with grain refinement of medium carbon steel AISI 1045 having different initial microstructure resulting from thermal and/or thermomechanical treatment (TM) applied prior severe plastic deformation. In case of TM treated steel, structure refinement was conducted in two steps. Preliminary structure refinement has been achieved due to multistep open die forging process which provided total strain εef ∼ 3. Uniform and fine recrystallized ferrite structure with grain size of the order of 2-5 μm and with nest-like pearlite colonies was obtained. The further grain refinement of steel samples having different initial structure was accomplished during warm Equal Channel Angular Pressing (ECAP) at 400°C. The microstructure development was analyzed in dependence of effective strain introduced (εef ∼ 2.5 - 4). Employment of this processing route resulted in extensive deformation of ferrite grains where mixture of subgrains and ultrafine grain was found regardless the preliminary treatment of steel. As straining increases the dynamic polygonization and recrystallization became active to form mixture of polygonized subgrains and submicrocrystalline grains having high angle boundaries. The intensive straining and moderate ECAP temperature caused the partial cementite lamellae fragmentation and spheroidization as straining increased. The lamellae cementite spheroidization was more extensive in TM treated steel samples. The deformation behavior of for both steel structural state confirm the strength increase; however the work hardening behavior was modified with respect to initial structure of steel prior SPD processing.


Zrnik J.,Comtes Fht | Dobatkin S.V.,RAS Institute of Metallurgy | Kraus L.,Comtes Fht | Raab G.,Institute of Physics of Advanced Materials
Steel Research International | Year: 2013

The present work, deals with grain refinement of medium carbon steel AISI 1045 (0.45% C), having different initial ferrite-pearlite microstructure resulted from thermal and thermomechanical treatment (TM). The purpose of TM steel processing was to refine ferrite and modify pearlite lamellae structure. The final grain refinement of steel structure was then accomplished during warm Equal Channel Angular Pressing (ECAP) at 400°C. Employment of this processing route, in dependence of the applied effective strain Ïμef, resulted in extensive deformation of ferrite grains and cementite lamellae fragmentation. When applying higher shear stress (Ïμef = 4) the mixed structure of subgrains and ultrafine grains was formed within ferrite phase, regardless the initial steel structure morphology. In pearlite grains, modification of cementite lamellae due to shearing, bending, twisting, and breaking was found efficient as straining increased. Processes of dynamic polygonization and recrystallization in deformed structure also contributed to submicrocrystalline grains formation in deformed structure. Comparing results the course of lamellae cementite spheroidization was then more efficient in prior TM treated steel. The tensile deformation results confirmed the strength increase, however deformation behavior and strain hardening generally for different initial structural conditions of steel, showed diversity. In order to modify initial microstructure of medium carbon steel AISI 1045 the thermal and thermomechanical (TM) treatments are applied. The final grain refinement of both steel structural states is thereafter completed during ECAP severe plastic deformation (SPD) applying different strain Ïμef. SPD processing resulted in extensive deformation of ferrite grains and cementite lamellae modification. Evaluating results, the course of grains refinement and lamellae modification is more effective in steel, which was preliminary modified by TM. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Jozef Z.,Comtes Fht | Jozef Z.,Technical University of Košice | Sergey D.V.,RAS Institute of Metallurgy | George R.,Institute of Physics of Advanced Materials | And 2 more authors.
Revista Materia | Year: 2010

The present work deals with grain refinement of medium carbon steel, having different initial microstructure, modified by either thermal and/or thermomechanical treatment (TM) prior severe plastic deformation. In case of TM treated steel, structure refinement was conducted in two steps. Preliminary structure refinement has been achieved due to multistep open die forging process which provided total strain of 3. Uniform and fine recrystallized ferrite structure with grain size of the order of 2-5 μm and with nest-like pearlite colonies was obtained. The further grain refinement of steel samples having different initial structure was accomplished during warm Equal Channel Angular Pressing (ECAP) at 400°C. The microstructure development was analyzed in dependence of effective strain introduced (εef ~2.5 - 4). Employment of this processing route resulted in extensive deformation of ferrite grains where mixture of subgrains and ultrafine grain was found regardless the preliminary treatment of steel. The straining and moderate ECAP temperature caused the partial cementite lamellae fragmentation and spheroidization as straining increased. The cementite lamellae spheroidization was more extensive in TM treated steel samples. The tensile behavior was characterized by strength increase for both structural steel states; however the work hardening behavior was modified in steel where preliminary TM treatment was introduced to modified coarse ferrite-pearlite structure.


Zrnik J.,Comtes Fht | Dobatkin S.,RAS Institute of Metallurgy | Raab G.,Institute of Physics of Advanced Materials
Materials Science Forum | Year: 2014

The work presents the results on grains refinement of steel containing 0.45 wt pct carbon resulted from severe plastic deformation (SPD). Different steel structures from prior solutioning and/or thermomechanical treatment were prepared for deformation experiments. A coarse grain ferrite-pearlite structure was achieved applying solutioning. By application of thermomechanical (TM) controlled forging process, performing multistep open die forging, the refined ferrite-pearlite mixture was prepared. Final structure refinement of steel, having different initial structure, was then accomplished applying warm Equal Channel Angular Pressing (ECAP) at 400°C. Employment of this processing route resulted in extensive deformation of ferrite grains and cementite lamellae fragmentation. Applying the highest shear stress (εef - 4) the mixed structure of subgrains and ultrafine grains was present within the ferrite phase. In pearlite grains, modification of cementite lamellae due to shearing, bending, twisting and breaking was found. The coarse cementite lamellae spheroidization was more efficient in prior TM treated steel. The tensile deformation records confirmed strength increase and diversity in strain hardening behaviour. © (2014) Trans Tech Publications, Switzerland.

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