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Severe Plastic Deformation
Laszlo S. TothLaboratoire d’Etude des Microstructure et de Mécanique des MatériauxLaboratoire d’Etude des Microstructure et de Mécanique des Matériaux
Université de Metz, France
Laboratoire d’Excellence Design des Alliages Métalliques pour Allègement des Structures, DAMAS
Action Nationale de Formation métallurgie fondamentale.Aussois 22-25 octobre 2012
Content
• For Introduction: Keywords and objectives• Strain modes in SPD• Strain hardening • Microstructure features• Texture evolution • Texture evolution • A model of grain refinement• Effect of strain path on grain refinement and
texture• Strong points and future key issues
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Keywords and objectives
Keywords:
SPD: Severe Plastic Deformation, Hyperdéformation
UFG: Ultra Fine Grain
BNM: Bulk Nanostructured Materials
NanoSPD: Nanostructured Materials by SPD
NanoSPD6: Metz, 2014, June 30-July 4
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Objectives:
To apply SPD for reducing the grain size.
Modern SPD techniques: obtain large strains without changing the shape!
SPD transforms the microstructure, introduces very large amount of new GB.
Grain boundary engineering
Explore the properties between nano and conventional grain structures, in the UFG regime.
Publication activity in SPD
Number of publications Number of citations
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Paradox of strength vs ductility
The paradox of strength vs ductility; the nano-Ti and nano-Cu
has superior propertiesRZ Valiev, IV Alexandrov, TC Lowe, et al., J Mater Res 17 (2002) 5
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NANO
Palladium, HREM
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Static Model (steel balls)
For microstructure teaching
5 nm
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For microstructure teaching-dislocation
b
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SPD processes
ECAP (ECAE), NECAP, ARB, HPT, HPTT
fixed anvil
twisting anvil
before after
1 2
3
4
Next pass
before HPTT
after HPTT
Equal Channel Angular Extrusion Non-Equal Channel Angular Extrusion High pressure torsion High Pressure Tube Twisting
Accumulated roll-bonding
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SPD in LEM3, Metz
ECAE
Twisting Mandrel
Fixe Mandrel
Sample
Compression
HPTTAction Nationale de Formation
métallurgie fondamentale. Aussois 22-25 octobre 2012
Experimental evidence for grain fragmentation in SPD
100 mµ 100 mµ
5 mµ Shear, γ = 4
Al, CP, defomed by HPTT – Arzaghi, thesisAction Nationale de Formation
métallurgie fondamentale. Aussois 22-25 octobre 2012
Acta Materialia 60 (2012), pp. 4393-4408
The strain mode in SPD
Strain field in ECAE(simple shear model)
yx’
:velocity gradient
:
1 1 01
1 1 02
0 0 0
velocity gradient
− −
x
y’0 1 0
0 0 0
0 0 0
−
0 0 0
Deformation state:compression, tension+ rigid body rotation
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Experiment, Segal, 1999
Gholinia, Bate, Prangnell, 2002 Beyerlein, Tome, 2004
0
2
4
6
0 2 4 6
Toth, 2003
Gholinia, Bate, Prangnell, 2002
αα
Φ
β α
Φ
Central fanLow deformation
Rotating region
Beyerlein, Tome, 2004
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Strain mode in HPTT et HPT
HPTHPTT
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Strain heterogeneity in HPTT
4
6
8
10 Tube wall
γ
Experimental Simulated
Local strain
r = ar = b IF steel
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6.4 6.6 6.8 7.0 7.2 7.4 7.60
2
4
Transition zone
Radius [mm]
Pougis et al. Scripta Materialia, 66 (2012) 773-776
Average strain:( )b
a
rdr
r
γθ = ∫ ln( / )b a
θγ =
Strain hardening in SPD
HPTT
During HPTTECAE ( )
( )2 2
lnT b a
b a hτ
π=
−
model
Arzaghi et al. Acta Materialia 60 (2012), pp. 4393-4408L. Toth, Computational Materials Science 32 (2005) 568–576
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0
50
100
150
200
250
300
350
0 2 4 6 8 10 12 14 16 18
Yσ [MPa]
Compression Test
Ring Hoop Tension Test
( )HPTTγ
After HPTT
(a) (b)
Compression disks
Tube θ
8 mm
1
5 mm
3 mm
Tube with Rout = 8mm
Reduced section
D-blocks
Pin
60°
Al 1050Ring-hoop tensile test
compression
Microstructure features
Toth et al., Acta Materialia, 58 (2010) 6706-67163-pass ECAECu
0 5 10 15 20 25 30 35 40 45 50 55 60 650.00
0.01
0.02
0.03
0.04
0.05
In grain interior
At grain boundary
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int int( ) ( ) ( )total OBG OBGf fυ θ υ θ υ θ= +new grain in interior of old grain
Microstructure in ARB
B. Beausir, T.U. DresdenAction Nationale de Formation
métallurgie fondamentale. Aussois 22-25 octobre 2012
Al pure + Al 1050
Texture evolution
measured simulated
pass 1
pass 2
ECAE, Route A, Copper
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A new quantitative grain fragmentation model
A new model is proposed for grain fragmentation that is based on lattice curvature. The lattice curvature is produced by the grain boundaries where lattice rotation is slowed down.
László S. Toth, Yuri Estrin, Rimma Lapovok, Chengfan GuActa Materialia 58 (2010) 1782-1794
The new model predicts:
Grain size evolution and distribution
Misorientation distribution of grains
Misorientation of cell walls
Texture development
Strain hardening
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Lattice curvature in a grain
Uniformlattice rotation
Grain
Initial lattice plane
Distorded lattice plane
zone affected by GB
zone not affected by GB
Al-Si alloy, Skjervold, 1995
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Experimental evidence
Ti rolled to 2% -Fundenberger-Beausir
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Lattice curvature in experiments
EBSD map of GND density, Cu ECAP 1 passC.F. Gu, L.S. Tóth, B. Beausir, Scripta Materialia, 2012.
1GND ij ijb
ρ α α=
(2 ) 2 2 2 2 212 13 21 23 33
1Dρ α α α α α= + + + +
:ijα Nye’s dislocation density tensor
12 13 21 23 33GND bρ α α α α α= + + + +
(3 ) (2 )3 5GND GND
D Dρ ρ=
Assuming isotropy:
) 14 2(3 4.38 10 mGND
Dρ −= ×
x1015m-2
0.33 0.7 1.3 2.0 2.7 3.35
BC
0
Lattice curvature in a grain
OR
µ
A
B
C
d
Initial
Rotated-curved1
Curvature-induced dislocation density:
D/2
Lattice rotation
Rotated-curved1CIDb
Rκ ρ= =
( )( ) ( )2
12sin, 1, 2, or 3.
cos cos 8CID k k
bD
µρ
µ µ
Ω= =
− Ω + Ω +
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Grain fragmentation procedure
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Grain fragmentation
GBSG G SGΩ = Ω + Ω& & &
Sugbrain rotations:
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Application to ECAP of copper
Measured:Simulated with grain refinement:
Passs-1
Simulated without grain refinement:
Taylor model, µµµµ=0.5, 500 initial grains 6 million grains
Passs-2, Route Bc
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Grain size
10
20
30
gra
in s
ize
[mik
ro m
]
Measured
Simulated 0 1 2 3 4 5D (micron)
0.0
0.5
1.0
1.5
2.0
2.5
Freq
uenc
y de
nsity
0.0 0.5 1.0 1.5 2.0 2.5von Mises strain
0
10
Ave
rage
Simulated
D (micron)
0 1 2 3 4 5D (micron)
0.0
0.5
1.0
1.5
2.0
2.5
Freq
uenc
y de
nsity
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Misorientation distribution (NNMD)
0.025
0.03
0.035
0.04
experiment
M. Arzaghi, Ph.D. thesis, Metz, France, 2010
Al 1050 HPTTArzaghi et al. Acta Materialia 60 (2012), pp. 4393-4408
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0
0.005
0.01
0.015
0.02
0 10 20 30 40 50 60
Next-grain misorientation distribution Al 1050 HPTT, shear = 4
experiment
simulation
The dislocation-cell based hardening model
Cell wall:
12 /3
1 2 00
3 * (1 )6 * (1 )(1 ) (1 )
n
r ws wg wrws r ws
ffk
bdf fb
β γ ρ ρ γβ γρ ξ ξ γ ργ
−− + −= − + − −
& &&& &
&
2/3
1 2
3 * (1 )6 * (1 ) r ws wgrwg
ff
bdf fb
β γ ρ ρβ γρ ξ ξ− +−= +
&&&
Y. Estrin, L.S. Toth, A. Molinari, Y. Bréchet, Acta materialia, 46, 5509-5522, 1998, cited 182 timesL.S. Toth, A. Molinari, Y. Estrin, J. Eng. Mat. Techn. 124, 71-77, 2002, cited 70 times.
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slip from the cells
FR sources for dislocations coming from the cell
annihilation (cross slip)
Cell interior:( )
1
013 0
61* *
3 1
n
w c cc w c ck
b bd f
ρ γ γρ α γ β γ ργ
−
= − − −
& && & &
&
by FR sources from the walls
flux to the walls
Hardening
400
600
ress
[MP
a]
Predicted strain hardening curve
pass 1 pass 2
0.0 0.5 1.0 1.5 2.0 2.5von Mises strain
0
200
Equ
ival
ent s
tr
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Dislocation densities
2E+16
3E+16
4E+16
ion
dens
ity [1
/m]
rtotal
rwall
pass 1
pass 2
0.0 0.5 1.0 1.5 2.0 2.5von Mises strain
0E+0
1E+16
disl
ocat
i
rGND
rcell
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Cell-wall misorientation
2
3
4
rient
atio
n [°] pass 2pass 1
wgbdθ ρ=
0.0 0.5 1.0 1.5 2.0 2.5von Mises strain
0
1
2
Cel
l-wal
l dis
or
pass 1
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Strain path effect on grain refinement
Simulated (continuous lines) and experimental (symbols) development of average grain size obtained in ECAE and rolling
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C.F. Gu, L.S. Toth, M. Arzaghi, C.H.J. Davies,Scripta Materialia, 64 (2011) 284–287
Strain reversal effect on texture and grain refinement
Route C two-pass measured texture
Route C ECAEC.F. Gu and L.S. Tóth,Acta Materialia, 59 (2011) 5749-5757
Route C two-pass measured texture
Simulated texture by traditionalVPSC model
Simulated texture by the new grain refinement model
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0 1 2 3 4 5Grain size (micron)
0.0
0.5
1.0
1.5
Fre
quen
cy
0 1 2 3 4 5Grain size (micron)
0.0
0.5
1.0
1.5
Freq
uenc
y
Pass 1 Pass 2
Grain size
C.F. Gu, L.S. Toth, C.H.J. Davies,Scripta Materialia, 65 (2011), 167-170
Strong points and future key issues
Strong points:
- SPD deformation techniques can produce ultra fine grain microstructures with enhanced mechanical properties in bulk form.
- Grain sizes are in the range of sub-micron, in between the minimum grain sizes by DRX et nano-structures, readily feasible
- BNM materials are excellent candidates for biomechanics applications and micro-parts.
Future keys issues:
- Up-scaling from laboratory to industrial processes.
- Mastering of microstructure variations grand potential in metallurgy
- Understanding the grain subdivision process
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Fundamental publications in SPD
Bulk nanostructured materials from severe plastic deformation, Valiev, RZ; Islamgaliev, RK; Alexandrov, IV, PROGRESS IN MATERIALS SCIENCE 45, 2000, 103-189, 2622citations
Principles of equal-channel angular pressing as a processing tool for grain refinement, Valiev, Ruslan Z.; Langdon, Terence G. PROGRESS IN MATERIALS SCIENCE 51 2006 881-981, 972citations
STRUCTURE AND PROPERTIES OF ULTRAFINE-GRAINED MATERIALS PRODUCED BY SEVERE PLASTIC-DEFORMATION, VALIEV, RZ; KORZNIKOV, AV; MULYUKOV, RR, MATERIALS SCIENCE AND ENGINEERING 168 1993141-148, 779citations
Ultra-fine grained bulk aluminum produced by accumulative roll-bonding (ARB) process, Saito, Y; Tsuji, N; Utsunomiya, H; et
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Ultra-fine grained bulk aluminum produced by accumulative roll-bonding (ARB) process, Saito, Y; Tsuji, N; Utsunomiya, H; et al. SCRIPTA MATERIALIA 39 19981221-1227,462citations
Producing bulk ultrafine-grained materials by severe plastic deformation, Valiev, RZ; Estrin, Y; Horita, Z; et al., JOM 58 200633-39, 407citations
Nanostructuring of metals by severe plastic deformation for advanced properties, Valiev, R, NATURE MATERIALS 3 2004511-516, 355citations
Analysis of texture evolution in equal channel angular extrusion of copper using a new flow field, Toth, LS; Massion, RA; Germain, L; et al., ACTA MATERIALIA 52 20041885-1898, 109citations
Texture evolution in equal-channel angular extrusion, Beyerlein, Irene J.; Toth, Laszlo S., PROGRESS IN MATERIALS SCIENCE 54 2009, 427-510, 60citations
Acknowledgements
S. Suwas (Bangalore), W. Skrotzki (Dresden), M. Zehetbauer (Vienna),
I. Beyerlein (Los Alamos), C. Tomé (Los Alamos), C.F. Gu (Melbourne),
Y. Estrin(Melbourne), R. Lapovok(Melbourne), O. Bouaziz (ArcelorMittal), Y. Estrin(Melbourne), R. Lapovok(Melbourne), O. Bouaziz (ArcelorMittal), A. Hasani (Iran), A. Eberhardt (ENIM-LEM3), J.J. Fundenberger (LEM3),
L. Germain (LEM3), M. Arzaghi (LEM3), R. Arruffat (LEM3), B. Beausir (LEM3), A. Molinari (LEM3) , A. Pougis (LEM3)
ANR HYPERTUBE
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