Bom Claves EBSD

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  • 7/27/2019 Bom Claves EBSD


    Microstructural CharacterizationUsing EBSD

    Steven R. Claves

    Electron Backscatter Diffraction Sometimes referred to as

    Backscattered Kikuchi Diffraction (BKD)

    A diffraction technique for obtaining microtexturalinformation from small areas of bulk samples in thescanning electron microscope (SEM)

    Advantages Imaging & Crystallography Orientation of individual grains Simple sample preparation

    Disadvantages Crystalline samples Free of excessive

    plastic strain

    Components of an EBSD system

    SEM source High current High brightness

    Sample ~70 tilt

    BSE yield Forward scattered Detector position

    resolution Tilt correction Dynamic focus


    Components of an EBSD system

    Phosphor Screen Size Position

    # polesDetail

    Camera TV rate (speed/cost) CCD (quality)

    OIM* Computer scan control Data analysis

    *Sometimes referred to as ACOM(automated crystallographicorientation measurement)


    OIM* - (orientation imaging microscopy)

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    How the Pattern is Formed

    high energy electrons are elastically scattered byatomic planes in a crystallographic sample


    EBSP - Electron Backscatter Diffraction Patterns

    Si single crystal

    Map of the angular relationships between the atomic planes Orientation determined by indexing the EBSPs

    Three Euler Angles

    EBSP - Electron Backscatter Diffraction Patterns

    Si single crystal

    As the sample is rotated, the pattern changes toreflect the new orientaion

    0 5

    10 15 20 25 30

    35 40 45 50 55

    EBSD Samples BSE yield depends upon elements

    Lateral resolution & depth as well

    EBSD is a surface sensitive technique Flat surface (irregularities ok for non-mapping applications) High dislocation densities mar pattern quality

    Mechanical polishing, 0.05 m colloidal silica Light etch to remove surface deformation Alternative final steps

    Lapping Electropolish / electroetch (non-anodizing) Chemical polish

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    Step 1: Loading the Sample Orientation data (i.e. angles) with respect to what?

    Sample must be aligned properly in microscope


    Crystallographic orientationrelated to sample orientation

    System geometry



    Step 2: Acquire a Background Use fast scan at low mag. to acquire an average

    pattern from many differently oriented grains Flat, even intensity

    Step 3: Single Grain EBSP Fix beam position (spot mode) within a grain Raw pattern will have weak contrast

    Step 4: Subtract Background Remove constant bkg to increase contrast (bkgs may also be divided or other manipulations)

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    History EBSP first observed in 1954 (Alam

    Venables & Harland 1973 SEM with video rate camera

    Background correction / flat fielding Eventually high gain CCD cameras

    Burns algorithm for edge detection (Wrights,Adams92)

    Hough Transform(Krieger Lassen, Jensen 92)

    Orientation Imaging: The Emergence of a New Microscopy B.L. Adams, S.I. Wright, K. Kunze Met Trans 24A 1993

    Hough Transform Sum up pixel intensities along line

    Move the position and angle of the line Convert Kikuchi bands (2D) to a point (1D)

    Hough Transform


    d i s t a n c e

    start with vertical linemove counterclockwise

    Step 5: Load Phase Information

    Phase page fromTSL software

    Calculated positionof poles from:

    Point group

    lattice parameters


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    EBSPs Poles are identified by their inter-relationships

    based upon known interplanar angles Can identify poles by eye using crystal symmetry

    3D cube showing the symmetryof the m( -3)m space group.



    Interplanar Angles Lattice parameter and space group will determine the

    interplanar angles (measured by distance on the pattern)


    FCC - Aluminum

    F m3m a = 4

    Step 6: Calibration & Indexing Distances between poles are fixed for system setup

    Calibration based upon screen position & WD Location of the poles on the pattern determines the


    EBSD Mapping

    Incidente- beam



    phosphor screen

    Diffracted patternsappear on screen

    Fiber-optic cableto video camera

    e- beam rasters across sample generating EBSPs Computer instantaneously indexes each point Records orientation data for each beam position

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    Microtexture A population of orientations measured on a

    grain-by-grain basis

    6xxx Al Alloy

    x,y 1, , 2 CI IQ phase

    Grain Mapping Computer determines point-to-point misorientations

    When angle exceeds a certain threshold a newgrain is declared

    Large Areas Capability to perform

    large area scans as well Stage scan Stage/beam scan combo.

    Limited by size of chamber and system geometry

    Stage / beam scanStage / beam scan

    Small Area Maps Unique Grain Map Each grain given specific color

    2.5 m step size

    EBSD limited by spatialresolution of SEM

    ! W ~ 0.5 m step size! Schottky ~ 5 nm

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    Orientation Maps

    Inverse pole figure grain map

    Grains of similar orientations are given like colors

    Note poor pattern quality atgrain boundaries

    Applications of EBSD

    [Micro]Texture Analysis Misorientation Angles & Special Grain

    Boundaries Grain Size (Pseudo) Strain Mapping via IQ index Phase Identification

    (phase determination)

    PF, IPF, & ODF

    Discrete -Pole Figure

    Contour - InversePole Figure

    Intensity - OrientationDistribution Function

    Pole Figures Display orientations of

    highest probability

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    Inverse Pole Figure Maps Orientation given with respect to a

    specific direction (ND, TD, RD)

    Extruded Al -fiber texture along RD

    EBSD Comparison

    Individual grains are given unique colors Good Agreement between the simulated

    grain map and the backscattered electronimage



    Grain Size Maps

    (Can also use linear intercept method)

    Misorientation Angle

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    Special Grain Boundaries Coincident Site Lattices (CSL)

    Grain boundary engineered Cu = 3,9,27

    Special Grain Boundaries Coincident Site Lattices (CSL)

    Grain boundary engineered Cu = 3,9,27 65% 3 twins

    Strain Measurements Wilkinson & Dingley(91)

    Plastic Strain Sharpness of band edges

    Wilkinson(96/97) Increase distance to camera Small (mrad) shifts in location of zone axes


    Phase IdentificationPhase determination

    Known phasesdifferent crystallographic properties

    Phase Identification Unknown phases In combination with EDS Searchable databases

    Phase Identification in a Scanning Electron Microscope Using

    Backscattered Electron Kikuchi Patterns R.P. Goehner & J.R. Michael J. Res. Natl. Inst. Stand. Technol., 101 , 301 (1996)

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    -Al8Fe2Si -Al9Fe2Si2

    Varying SEM Conditions Spot size / beam current, (nm / nA) Accelerating voltage, kV Working Distance, WD (mm) Tilt Angle, degrees ()

    Effect of Beam Size Greater beam sizes = more current

    Spot size / C1 current Gun bias

    Lower acquisition times Better quality patterns (increased accuracy)

    Largest possible beam size depends upon Grain size Desired step size

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    [ Cast 6xxx Al Sample ]2x2 binning (650 x 525)

    Spot size = 3 (35 nm) Current = ~ 0.1 nA

    Acquire time = 8s

    Spot size = 7 (0.58 m) Current = ~ 14 nA

    Acquire time = 0.2 s

    Effect of kV Changes width of bands

    Poles stay in same positions

    5 kV

    10 kV

    15 kV

    20 kV

    25 kV

    30 kV

    Effect of Working Distance

    Moves pattern center (Changes the area of

    maximum BSE intensity) Calibration is very






    16 mm 20 mm 24 mm 28 mm

    Effect of Tilt Angle Modifies BSE yield Changes the distance angle

    conversion Calibration is very important










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    EBSD 2 Metal Forming Examples

    Microtexture Variation

    X [100] ND{hkl}

    Z [001] RD

    S ur f a c e

    s ur f a c e

    Pole Figures

    Small, Equiaxed Cube texture


    Large, Elongated FCC shear texture


    Macro Photographs I Dead Metal Zone(DMZ)

    II Shear Intensive Zone(SIZ)

    III Transition Zone(SIZ 2)

    IVa Main DeformationZone (MDZ)

    IVb - Negative Flow Angle(MDZ 2)









    10 mm

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    Etched in BarkersReagent Grain contrast under

    polarized light Boundaries appear


    Record angle withrespect to extrusiondirection

    extrusion direction

    BILLETcenterline surface

    49 III


    Record metal flow direction (angle)

    c e n t e r

    c e n t e r

    s ur f a c


    PoleFigures Microstructural Detail

    Small step size