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What do we expect from DAFS ?
DIFFABS beamline setup
Perspectives
Simultaneous DAFS and XAFS analyses to evidence the Y- and Ti- species in nano-structured ODS steels
Direction de l’Energie NucléaireDirection déléguée aux Activités Nucléaires de SaclayDépartement des Matériaux pour le NucléaireService de Recherches Métallurgiques Appliquées
10th SOLEIL USERS’ MEETING – January 22nd – 23rd 2015
Denis Menut1, Jean-Luc Béchade1, Dominique Thiaudière2
1CEA, DEN, Service de Recherches Métallurgiques Appliquées, 91191 Gif-sur-Yvette, France2Synchrotron SOLEIL, Ligne de lumière DIFFABS, L’Orme des Merisiers, Saint Aubin BP48, 91192 Gif-sur-Yvette, France
4-elements SiliconDrift DetectorStandard XAFS
measurements in fluorescence
1-element Silicon Drift Detector
Ti Ka and Y Ka-edgeDAFS measurements
Sample keept in Bragg diffraction condition Vs
energy
To characterize the microstructure of neutron irradiated materials, various experimental tools are available at the present time in nuclear environment: SEM, TEM, APT, RBS and NRA… However, these techniques are local probes and bring information for an extremely limited sample volume which could be not representative of the whole volume. Therefore, a good statistic can only be obtained by performing many examinations which are very time consuming.
Information from other techniques such as APT, TEM and XRD may be useful to help in analyzing the XAFS data.
However, the interpretation of XAFS data for industrial material where the absorbing atom studied is located in various secondary phases (showing different compositions, structures, densities, and grain sizes down to few nanometers), even in the matrix, is more challenging than for a quite homogeneous and “pure” material, where target species are clearly located in a specific phase.
To address this issue, Diffraction and Absorption analyses using synchrotron sources are of utmost interest: X-Ray Diffraction (XRD) patterns allow us to identify the precipitates structural changes from line-profile analyses of diffraction peaks,X-ray Absorption Fine Structure (XAFS) spectroscopy is particularly useful for studying, at the atomic scale, the local structure around a specific absorbing atom within the material that possess short-range (up to about 6 Å) or no translational order (amorphous structure).
It has enhanced capabilities compared to the separate techniques:DAFS provides EXAFS- and XANES- like information for the specific
subset of atoms selected by the diffraction condition.
DAFS combines into a single technique:
with
by measuring the elastic Bragg reflection intensities versus photon energy.
The long-range order and crystallographic sensitivities of XRD
The spectroscopic and short-range order sensitivities of XAFS
ODS steel grade : DYElaborated by mechanical alloying with the nominal composition (in Wt%):
Fe-13Cr-1.5Mo-2.2Ti-0.5Y2O3
Material supplied as 9 mm diameter extruded rod. After a 15 min thermal treatment at 1050°C, a final full day treatment was performed at 800°C
to induce the -phase precipitation (Fe36Cr12Mo3Ti7)
Enhanced mechanical properties due to reinforcement by homogeneous dispersion of nano-sized Y-Ti-O hard particles (~0.2 to 0.6 Wt%) that precipitate from the Fe-Y-Ti-O solid solution during the consolidation
Their composition and structures are still not well understood
P. Dubuisson et al.,ASTM STP 1325 (1999)
882-898I. MONNET et al., JNM 335
(2004) 311-321
Massiveintergranular
-phaseprecipitates
Oxides
Mean particle radius: ~10 nm (< 25nm) larger oxides ranging 25 – 500 nmMean particle spacing: ~90 nm
0
50
100
150
200
250
300
350
400
1.98 2.48 2.98 3.48 3.98
Inte
nsity
(Sqr
t) (a
.u.)
d-spacing (Å)
at 4.9 keVat 16.9 keV
-Fe(110)
*
* *
-phase(120)
(111)(120)
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
0.017
0.018
0.019
0.020
0.021
0.022
0.023
0.024
0.025
0.026
0.027
4.90 5.00 5.10 5.20
-F
e DA
FS ra
tio (a
.u.)
-ph
ase
DAFS
ratio
(a.u
.)
Energy (keV)
0.0000
0.0002
0.0004
0.0006
0.0008
0.0010
0.0012
0.117
0.118
0.119
0.12
0.121
0.122
0.123
0.124
0.125
0.126
0.127
4.9 5 5.1 5.2
XAFS
ratio
(a.u
.)
DAFS
ratio
(a.u
.)
Energy (a.u.)
0.0015
0.0025
0.0035
0.0045
0.0055
0.0065
0.0075
0.0085
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
16.95 17.15 17.35 17.55 17.75
XAFS
ratio
(a.u
.)
DAFS
ratio
(a.u
.)
Energy (keV)
XRD analyses
y = 3.48x2 - 51.65x + 244.07R² = 1
69
70
71
72
73
74
75
4.85 4.9 4.95 5 5.05 5.1 5.15 5.2 5.25
-ph
ase
(120
) diff
racti
on ll
ine
Max
imum
inte
nsity
pos
ition
in 2
(°)
X-ray energy (keV)
Energy Scan from
(keV)
To energy (keV)
Exposure time (s)
Energy step (eV)
4.9000 4.9640 20 2 4.9645 4.9900 20 0.5 4.9910 5.2000 20 1
Energy Scan from
(keV)
To energy (keV)
Exposure time (s)
Energy step (eV)
16.950 17.058 30 2 17.060 17.200 30 1 17.202 17.800 30 2
Elastic Bragg intensities Vs photon energy calibration for DAFSat Ti K-edge ( E0: 4.964 keV)
(the same procedure was used at Y K-edge (E0: 17.036 keV)
-phase simultaneous XAFS/DAFS analyses
Comparison of DAFS analyses at Ti K-edge between the -Fe
matrix and -phase precipitates
DAFS evidences:
That a significant part of Ti atoms are located in the -Fe BCC matrix [S. Liu et al., J. Nucl. Mater. 445, 50-56 (2014); P. He et al., J. Mat. Chem.
Phys. 136, 990-998 (2012)].
Both Ti and Y atoms (in a lower proportion) are observed in the intermetallic -phase(1 µm width and 10 µm length with a volume fraction estimated around 17%), thaught to be a quaternary phase of composition Fe36Cr12Mo3Ti7 [C. Zakine et Al., J. Nucl. Mater. 230, 78-83 (1996)].
However, DAFS measurements on Y-Ti-O nano-oxides were not possible due to their weak and broadened diffraction peaks.
Preliminary resultsData reduction and analyses
under progress
0
2000
4000
6000
8000
10000
12000
14000
68 70 72 74 76
-ph
ase
(120
) diff
racti
on ll
ine
Inte
nsity
(a.u
.)
2 (°)
at 4.9 keV at 5.0 keVat 5.1 keV at 5.2 keV
(SCK.CEN-Mol; 1975-1980)
DY has been neutron irradiated in Phénix as fuel pin claddings