Severe Plastic Deformation Laszlo S. Toth - .Severe Plastic Deformation Laszlo S. Toth ... BNM: Bulk

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  • Severe Plastic Deformation

    Laszlo S. TothLaboratoire dEtude des Microstructure et de Mcanique des MatriauxLaboratoire dEtude des Microstructure et de Mcanique des Matriaux

    Universit de Metz, France

    Laboratoire dExcellence Design des Alliages Mtalliques pour Allgement des Structures, DAMAS

    Action Nationale de Formation mtallurgie 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

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • Keywords and objectives

    Keywords:

    SPD: Severe Plastic Deformation, Hyperdformation

    UFG: Ultra Fine Grain

    BNM: Bulk Nanostructured Materials

    NanoSPD: Nanostructured Materials by SPD

    NanoSPD6: Metz, 2014, June 30-July 4

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

    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

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • 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

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • NANO

    Palladium, HREM

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • Static Model (steel balls)

    For microstructure teaching

    5 nm

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • Model for plastic deformation of nanocrystals

  • For microstructure teaching-dislocation

    b

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • 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

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • SPD in LEM3, Metz

    ECAE

    Twisting Mandrel

    Fixe Mandrel

    Sample

    Compression

    HPTTAction Nationale de Formation

    mtallurgie fondamentale. Aussois 22-25 octobre 2012

  • Experimental evidence for grain fragmentation in SPD

    100 m 100 m

    5 m Shear, = 4

    Al, CP, defomed by HPTT Arzaghi, thesisAction Nationale de Formation

    mtallurgie 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

    y0 1 0

    0 0 0

    0 0 0

    0 0 0

    Deformation state:compression, tension+ rigid body rotation

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • Experiment, Segal, 1999

    Gholinia, Bate, Prangnell, 2002 Beyerlein, Tome, 2004

    0

    2

    4

    6

    0 2 4 6

    Toth, 2003

    Gholinia, Bate, Prangnell, 2002

    Central fanLow deformation

    Rotating region

    Beyerlein, Tome, 2004

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • Strain mode in HPTT et HPT

    HPTHPTT

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • Strain heterogeneity in HPTT

    4

    6

    8

    10 Tube wall

    Experimental Simulated

    Local strain

    r = ar = b IF steel

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

    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

    = ln( / )b a =

  • Strain hardening in SPD

    HPTT

    During HPTTECAE ( )

    ( )2 2lnT b a

    b a h

    =

    model

    Arzaghi et al. Acta Materialia 60 (2012), pp. 4393-4408L. Toth, Computational Materials Science 32 (2005) 568576

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

    0

    50

    100

    150

    200

    250

    300

    350

    0 2 4 6 8 10 12 14 16 18

    Y [MPa]

    Compression Test

    Ring Hoop Tension Test

    ( )HPTT

    After HPTT

    (a) (b)

    Compression disks

    Tube

    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

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

    int int( ) ( ) ( )total OBG OBGf f = +new grain in interior of old grain

  • Microstructure in ARB

    B. Beausir, T.U. DresdenAction Nationale de Formation

    mtallurgie fondamentale. Aussois 22-25 octobre 2012

    Al pure + Al 1050

  • Texture evolution

    measured simulated

    pass 1

    pass 2

    ECAE, Route A, Copper

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • 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.

    Lszl 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

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • 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

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • Experimental evidence

    Ti rolled to 2% -Fundenberger-Beausir

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • Lattice curvature in experiments

    EBSD map of GND density, Cu ECAP 1 passC.F. Gu, L.S. Tth, B. Beausir, Scripta Materialia, 2012.

    1GND ij ijb

    =

    (2 ) 2 2 2 2 212 13 21 23 33

    1D = + + + +

    :ij Nyes dislocation density tensor

    12 13 21 23 33GND b = + + + +

    (3 ) (2 )3 5GND GND

    D D =

    Assuming isotropy:

    ) 14 2(3 4.38 10 mGND

    D =

    x1015m-2

    0.33 0.7 1.3 2.0 2.7 3.35

    BC

    0

  • Lattice curvature in a grain

    OR

    A

    B

    C

    d

    Initial

    Rotated-curved1

    Curvature-induced dislocation density:

    D/2

    Lattice rotation

    Rotated-curved1CIDbR

    = =

    ( )( ) ( )212sin

    , 1, 2, or 3.cos cos 8

    CID k kbD

    = =

    + +

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • Grain fragmentation procedure

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • Grain fragmentation

    GBSG G SG = + & & &

    Sugbrain rotations:

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • Application to ECAP of copper

    Measured:Simulated with grain refinement:

    Passs-1

    Simulated without grain refinement:

    Taylor model, =0.5, 500 initial grains 6 million grains

    Passs-2, Route Bc

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • 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

    Action Nationale de Formation mtallurgie fondamentale. Aussois

    22-25 octobre 2012

  • Misorientation distribution (NNMD)

    0.025

    0.03

    0.035