Crystallographic orientation maps obtained from ion and back scattered electron channeling contrast

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Crystallographic orientation maps obtained from ion and back scattered electron channeling contrast

Cyril Langlois, Clément Lafond, Thierry Douillard, Sébastien Dubail, Sophie Cazottes

To cite this version:

Cyril Langlois, Clément Lafond, Thierry Douillard, Sébastien Dubail, Sophie Cazottes. Crystallo-

graphic orientation maps obtained from ion and back scattered electron channeling contrast. 19th

International Microscopy Congress, Sep 2018, Sydney, Australia. �hal-02138699�

Crystallographic orientation maps obtained from ion and back scattered electron channeling contrast

LANGLOIS, C.

, LAFOND, C.

, DOUILLARD, T.

, DUBAIL, S.

and CAZOTTES, S.

1

MATEIS Laboratory, INSA , University of Lyon – CNRS (France),

Axon Square Ltd. (France)

I NTRODUCTION

For several years now, new directions have been explored to obtain orientation maps by other means than the classical Electron Back Scattered Diffraction (EBSD) setup, or to modify it aiming at improved information. Particularly, the channeling contrast may be used to obtain orientation maps, which is the approach presented here, called CHanneling ORientation Determination (CHORD) [1,2]. The main idea relies on the acquisition of an electron or ion image series when rotating a pre-inclined polycrystalline sample with respect to the beam. Along such image series, each (X,Y) pixel of the region of interest undergoes an intensity variation due to the channeling effect, that can be plotted as a function of the rotation angle. Such intensity profiles can be theoretically predicted for a given orientation of a crystal, as described in the following. The orientation is retrieved by a search in a database of theoretical profiles obtained by simulating intensity profiles for a large set of orientations. The principal issue is to model quantitatively for ions and electrons the channeling effect observed in such image series.

[1] Langlois C. et al., Ultramicroscopy 157 (2015), p. 65 [2] Lafond C. et al., Ultramicroscopy, 186 (2018), p. 146

[3] Newbury D. E.et al., Advanced Scanning Electron Microscopy and X-Ray Microanalysis, Springer (1986) [4] Singh S. & De Graef M., Microscopy and Microanalysis, 23 (2017), p. 1

A CQUISITION

e r

e r

e r

Initial tilt angle aroundex

Starting point: beam perpendicular to the sample surface

•

then tilting the sample 40° for ions ; 10° for electrons

•

then rotation of the sample around the tilted normal one image acquisition every rotation step (automated)

Raw ion image series

Signal detection:

•

e- back scattered electron detector

•

Ga

ion-induced secondary electron detector

-image series

C HANNELING C ONTRAST

P OST - TREATMENTS

From raw image series Alignment

Crop on the region of interest Denoising (eventually)

360°

0°

90°

180°

270°

Intensity

40 80 120 160 200

0 50 100 150 200 250 300 350

Angle (degree)

Grain 1

Intensity

40 80 120 160 200

0 50 100 150 200 250 300 350

Angle (degree)

Grain 2

An experimental intensity profile is obtained for each (X,Y) position.

Generation of theoretical intensity profiles for ions and electrons

•

construction of a database of theoretical intensity profiles

•

pick up an intensity profile at (X,Y) position

•

explore the database to find the closest theoretical one

•

assign the corresponding theoretical orientation to the (X,Y) position

E LECTRON C HANNELING M ODELIZATION

Based on similarities with Electron Channeling Pattern acquisition (ECP) ; diffraction including dynamical effects using M. De Graef EMsoft codes [4].

e r

e r

e r

10° tilt around e_x

10°

26°

ECP simulated using EMsoft codes [3] for a given orientation (ϕ1Φ ϕ2)

Intensity

40 80 120 160 200

0 50 100 150 200 250 300 350

Angle (degree)

I ON C HANNELING M ODELIZATION

Ballistic description ; numerical approach based on the relationship between the « shadow » of the structure and the detected intensity

Grain 2

R EFERENCES

S TRATEGY TO RECOVER THE ORIENTATION

Gathering the intensity along the ECP 10° circle…

For Euler orientation (

) and each rotation angle, the intensity in the profile is the sum of grey

levels in the projection.

• with an electron beam, the intensity received by the detector is monitored by back scattered diffraction including dynamical effects.

The channeling of the incident beam by crystallographic planes is responsible for the grey level difference between differently oriented grains in a polycrystalline material.

• if the ion beam is parallel to low index planes, the secondary electron are generated far under the surface. A low intensity is then detected.

More details on the channeling effect available in ref [3]

Crystallographic orientation maps obtained from ion and back scattered electron channeling contrast

LANGLOIS, C.

, LAFOND, C.

, DOUILLARD, T.

, DUBAIL, S.

and CAZOTTES, S.

1

MATEIS Laboratory, INSA , University of Lyon – CNRS (France),

Axon Square Ltd. (France)

10°

0°

eCHORD map (raw)

EBSD map (denoised)

Disorientation map eCHORD / EBSD BSE image series

50 µm

Tension 15 kV / WD : 7 mm Profile database: 1 million

theoretical profiles

200µm

E CHORD: EXAMPLES

10°

0°

eCHORD map (raw)

EBSD map

Disorientation map eCHORD / EBSD BSE image series

Tension 15 kV / WD : 7 mm Profile database: 1 million

theoretical profiles

230µm

Aluminium Nickel

I CHORD: EXAMPLES

iCHORD [001] IPF map EBSD [001] IPF map

(noise corrected)

S LIGHTLY DEFORMED COPPER SAMPLE

EBSD [010] IPF map (noise corrected) iCHORD [010] IPF map

C OBALT S UPERALLOY S AMPLE

A NGULAR RESOLUTION OF I CHORD MAPS – EXAMPLE ON I NCONEL SAMPLE

Disorientation distribution 6.5° ± 0.6°

with 500k profile database

0 3000 6000 9000 12000

4,2 5 5,8 6,6 7,4 8,29

Frequency

Disorientation (°) 30 µm

0°

10°

Original 6° apart Disorientation map

The idea: circular permutation of 6 frames in the image series Peak shift of 6° in the intensity profiles // Disorientation of 6°

between the two maps

Circular permutation of 6 images new image series

6° disorientation

0 100 200

0 60 120 180 240 300 360

Intensity

Rotation angle (°)

Original image series 6° image series

I

CHORD

0.6°

S AME EXPERIMENT WITH 4° DISORIENTATION FOR ELECTRONS E CHORD ANGULAR RESOLUTION

ESTIMATED TO 0.1°

P ERSPECTIVES

P

– eCHORD on duplex steel

Tension 15 kV / WD : 6.5 mm

• two different cubic structures

• close averageatomicnumber yellow: ferrite ; green: austénite ferrite(bcc) / austenite(fcc)

EBSD eCHORD

F AST CHORD

1. Reducing number of images in the series 2. Reducing dwell time per pixel Aluminium

360 images 45 images

eCHORD reference map

eCHORD map with 45 images 150 µm

10°

0°

Point-to-point disorientation map Tension 5 kV / WD: 7 mm

C ONCLUSION

The CHORD approach for orientation mapping is an interesting compromise between angular //spatial resolution and acquisition speed.

• More on phase discrimination capability oral presentation from C. Lafond on Monday 14:45, Meeting Room C4.1

• For a focus on acquisition and image treatments, oral presentation from C. Langlois on Tuesday 16:00, Meeting Room C4.11

Mixing iCHORD orientation mapping with secondary ion images for γ-γ’

phases discrimination

Secondary ion images iCHORD Orientation map

45 µm

P

– iCHORD on Ni superalloy

Easy superimposition of

both information

150 µm

Total acquisition time

• 12 seconds for 45 images

• 28 seconds of latency between images

(to be optimized) 45 images of size 200 x 150 pixels

200 ms per image

eCHORD reference map

eCHORD fast map (45 images)