S.K. Balijepalli, G. Barbieri, M. Cesaroni, G. Costanza, L. Ciambella,
S. Kaciulis, G. Maddaluno, A. Mezzi, R. Montanari, A. Varone
S.K. Balijepalli, L. Ciambella, S. Kaciulis, G. Maddaluno, A. Mezzi, R. Montanari
Application of W as armour material in ITER
1- Central solenoid
2- Shield/blanket
3- Active coil
4- Plasma
5- Vacuum vessel shield
6- Plasma exhaust
7- Cryostat
8- Poloidal field coils
9- Toroidal field coils
10- First wall
11- Divertor plates
Owing to its low physical sputtering rate, high
melting point and high thermal conductivity, W is
a candidate material for the divertor armour of
the international thermonuclear experimental
reactor (ITER).
It is expected to resist to the steady state heat flux
of 10 MW/m2, and transient high energy events,
like disruption, edge local modes and vertical
displacement events.
Study on bulk material
The bulk material has a purity of 99.97% and porosity of 5%.
Table - Young’s modulus E and yield stress σY up to 500 °C.
W has been heat treated at 500 °C and 800 °C with increasing soaking time up to 10
hours.
Examined by:
1.
2.
3.
4.
TEM
Light microscopy
X-ray diffraction (XRD)
Micro-hardness tests
TEM
As-received W
Microstructure is
characterized by well
defined grains containing
many dislocations.
The porosity is very low but
in some zones pores of
small size (~ 30 nm) can be
observed.
TEM
Heat treatments at 500°C do not induce remarkable changes of grain size, only a weak
decrease of dislocation density has been observed. No porosity was detected.
500 °C, 4 hours
Light microscopy
1 h 800°C
2 h 800°C
5 h 800°C
10 h 800°C
140
120
Heat treatments at 500 °C do
not induce remarkable changes
of grain size. On the contrary,
grain growth is observed after
heating at 800 °C.
110
100
90
80
70
60
50
0
2
4
6
8
10
Time (hours)
800 °C
480
500 °C
470
Micro-hardness (HV)
Mean grain size (m)
Grain size
800 °C
500 °C
130
460
450
440
430
420
410
Micro-hardness test
0
2
4
6
Time (hours)
8
10
2500
X-Ray Diffraction
110
1200
10 hours at 800 °C
As-received
X-Ray Intensity (a.u.)
2000
110
211
1500
200
As-received
220
310
222
321
1000
500
10 hours at 800 °C
1000
0
X-Ray Intensity (a.u.)
20
40
50
2 deg
800
600
After the heat treatment at increasing
soaking time the peak profile becomes
progressively narrower and the centre shifts
towards lower angles.
400
200
0
17,0
30
17,5
18,0
2(deg)
18,5
19,0
Dislocation density evolution
10
2,0x10
800 °C
500 °C
-2
Dislocation density (cm )
10
1,5x10
The total line broadening T is due to
two contributions, the size of
coherently diffracting domains (D),
i.e. the grains, and the micro-strains
( ):
T   D   
10
1,0x10
9
5,0x10
0
2
4
6
8
Time (hours)
10
K
 2 tan 
D cos 
D = domain size,
 = average micro-strain,
 = Bragg angle,
= wavelength,
K = constant (= 0.89).
Being D very large, i.e. of the order
of some tens of microns, D can be
considered negligible thus T   .
The dislocation density  calculated by the Williamson-Smallman relationship:
 =  ε2 / k0 b2
where  = 16 is a constant, b = 0.274 nm the modulus of Burgers vector and k0  1 a factor
depending on dislocation interaction.
W deposited by Plasma Spraying
W
Deformazioni dovute a tensioni
residue
Interlayer

d Sper  d Calc
d Calc
W su AISI 420
Lega CuCrZr
W
AISI 316L
W + Al-12%Si
W deposited on CuCrZr
Without interlayer
W (110)
7000
6000
4000
Cu (111)
Intensity (a.u.)
5000
3000
2000
1000
25°C
0
16
17
18
19
2 (°)
With interlayer
20
21
W deposited on AISI 316L
W (110)
2000
Intensity (a.u.)
Fe (110)
W deposited on AISI 420
1500
460 °C
1000
500
25 °C
0
17
18
19
2(°)
20
21
L. Ciambella, R. Montanari
ENEA is the coordinator of an European project called “MATTER” (MATerial Testing &
Rules) based on the characterization of new materials able to work under extreme
conditions for the development of new generation nuclear systems (Generation IV, ADS
etc.).
The aim of this research is the characterization of T91 steel with FIMEC indentation test
in order to determine the principal mechanical properties of this steel like yield stress.
Before the characterization is necessary to optimize and standardize the indentation test
in order to draft a pre-normative for mechanical properties determination.
Introduction to FIMEC
(Flat-top cylinder Indenter for MEchanical Characterization)
The indentation test is one of the most common techniques for the mechanical characterization
of materials.
FIMEC is a flat-ended cylindrical indentation technique which employs a cylindrical punch
made of sintered tungsten carbide. Unlike other indentation tests employing punches of
different shape (pyramid, sphere, cone etc.), the contact area between punch and material is
constant during the test.
yield stress;
elastic modulus E;
ductile to brittle transition temperature (DBTT);
surface creep;
stress relaxation.
FIMEC apparatus
•
Linear actuator: electro-mechanical drive equipped with a
stepping motor. The motor rotation is transmitted to a ball screw
by a precision reduction gear; the ballscrew converts the
rotation at the gear output to translation.
•
Linear Voltage Displacement Transducer (LVDT): measures the
displacement between the sample holder and the indenter .
•
Load cell: located under the sample holder measures the applied
load .
•
Cylindrical punch: made of tungsten carbide (WC), providing
high rigidity and strength.
•
Heating system: Tubular furnace , which guarantees a constant
temperature (±2 °C) in a vertical zone of about 10 cm, where
punch, sample holder and sample are located.
FIMEC PARAMETERS
Advancement speed
(mm/s)
1 · 10-4 - 2 · 10-2
LVDT resolution (mm)
1
Load cell resolution (N)
1
Cylindrical punch diameters
(mm)
Range Temperature (°C)
0,5 ÷ 1
- 196 ÷ 600
The pressure-penetration curves
During a FIMEC test the applied load and the penetration depth are measured; it is possible
to determine pressure (p) vs. penetration depth (h) curves by dividing loads by the punchsurface contact area A.
Elastic stage up to a pressure load pL.
Below pL the curve is fully reversible and
no permanent deformation occurs on the
sample.
The first plastic stage is almost linear
and end at a pressure py : the imprint
shows permanent sharp edges.
The second plastic stage occurs for p >
py and is characterized by a sudden slope
decrease. During this stage the materials
start to protrude around the imprint.
The third plastic stage shows a trend
with an almost constant slope.
Under standardised conditions (penetration rate  0.1 mm/min and deformation rate in
tensile test 10-3 s-1), it is possible to determine the value of the yield stress Y from the pY
value, according to the equation below:
pY  3Y
This equation has been verified to be valid for several metals (steels, Cu alloys, Ti alloys, Al
alloys, metal matrix composites, superalloys etc.).
The Method description: Analysis of LP curves
Owing to the inhomogeneous plastic behaviour in the initial part of punch penetration (1st plastic stage)
is quite difficult to find a relationship suitable to describe this stage and useful for directly identifying
the pressure pY for all the metals. On the contrary, the 2nd and 3rd stages, where the plastic deformation
occurs in a large volume under the punch, can be described by the equation:
p = K (h0 + h)n
The method can be divided in 3 steps.
1- First of all the experimental pressure-penetration curve is filtered to remove possible noise.
2- The values of K, h0 and n are determined which give the best fit of the 2nd and 3rd stages of the
curve.
3- The pressure pY is calculated at a fixed depth
hY = h0 + h = 0.009 mm
by substituting into this equation the values of K and n determined by the best fitting.
Fitting of T91
For T91 steel the values K and n are:
4500
Experimental curve
Fitting
4000
K = 4347 N·mm-(n+2)
n = 0.193
h0 + h = 0.009 mm
Pressure (MPa)
3500
3000
Replacing these values in the previously
described equation:
2500
2000
p = K (h0 + h)n
1500
It is possible to obtain the pressure pY:
1000
500
pY = 1752 MPa
0
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
Penetration depth (mm)
Since the yield stress provided by standard tensile stress is:
FIMEC = pY /3 = 584 MPa
Y =580 MPa
To assess the general validity of the algorithm some materials relevant for nuclear applications have
been tested at increasing temperatures and the results compared with those obtained by tensile tests
with standard probes.
Material T [°C]
Manet-II
The Table reports for each
material the parameters K,
h0 and n giving the best
fit, the value FIMEC
determined through the
algorithm, the yield stress
Y from standard tensile
test and the relative
difference .
The Y values of tensile
tests have been taken from
the literature.
20
200
300
400
500
F82H mod. 20
100
200
300
400
500
Eurofer-97 20
100
200
300
400
500
EM-10
20
250
500
K
5575
4842
4573
4407
3945
4402
3925
3768
3476
3252
3021
4737
4251
3891
3775
3507
3133
4639
4036
3505
h0 [mm]
-0,05211
-0,03397
-0,04587
-0,04114
-0,03743
-0,03354
-0,03977
-0,03953
-0,03728
-0,03371
-0,04029
-0,03113
-0,03345
-0,03363
-0,03196
-0,03187
-0,02515
-0,05155
-0,03755
-0,02596
n
FIMEC
Y
 = (Y – FIMEC) / Y
0,218
0,212
0,210
0,210
0,209
0,213
0,209
0,207
0,203
0,187
0,185
0,222
0,218
0,208
0,206
0,205
0,204
0,248
0,246
0,239
[MPa]
664
594
566
546
489
537
488
474
445
448
421
555
507
486
476
445
399
481
422
379
[MPa]
655
607
602
548
465
544
501
478
469
452
407
546
507
484
470
447
396
491
433
361
-0,01
0,02
0,06
0,003
-0,05
0,01
0,03
0,01
0,05
0,01
-0,03
-0,02
-0,001
-0,005
-0,01
0,005
-0,01
0,02
0,03
-0,05
Why PbBi?
Liquid Pb–Bi eutectic (LBE) alloy has been selected as a coolant and neutron spallation
source for the development of MYRRHA, an accelerator driven system (ADS).
Low melting temperature (~125°C)
 high boiling point (~1670°C)
 excellent chemical stability
 It is also possible to eliminate secondary heat transport
loops and associated intermediate heat exchangers because
LBE does not exothermically react with water and air.

The ADS technology however requires special
operating conditions: the materials need to resist
temperatures ranging between 200-550°C under a high
energy neutron flux and in contact with the LBE: the
limitation of ADS life is due to the relatively low corrosion
resistance of structural materials in the LBE environment
The compatibility of structural materials with liquid LBE
at high temperature is one of the key issues for the
commercialization of such fast reactors.

Material and experimental
The structural evolution of LBE has been
investigated by :
• Internal friction
• Dynamic modulus measurements
• High-temperature X-ray diffraction
After quenching the samples have been investigated by:
•Standard XPS
•Scanning photoemission microscopy (SPEM)
IF and dynamic modulus measurements
Experiments were carried out by employing the mechanical analyser VRA 1604.
NEW METHOD : Metal is cast inside hollow reed (stainless steel AISI 316), closed to one
end. After filling the reed is sealed.
Experimental data must be corrected from the contribution of the container measured in the
same conditions using not filled reeds.
0,010
Empty reed
0,008
E/E0
1,0
0,9
0,8
0,004
0,002
0,000
m2h
f 
2 12L2
E
0,7
Q-1
100
200
300
400
500
600
700
Temperature (°C)

R. Montanari, A. Varone
0,6
E/E0
Q
-1
0,006
IF and dynamic modulus measurements
0,010
Melting
Transformation start
1,0
0,008
0,9
0,006
0,8
0,004
0,002
0,000
E/E0
Q
-1
Transformation finish
0,7
100
200
300
400
500
600
Temperature (°C)
After melting the modulus of eutectic alloy decreases with nearly constant slope up
to 350 °C where drops and finally, above 520 °C, continues to decrease with a slope
very close to the initial one. In correspondence of the modulus drop two IF maxima
are observed.
R. Montanari, A. Varone
HT-XRD measurements
RDF  2r e UC Z m  
2
Q max
0
20
719°C
560°C(fine trasformazione)
350°C (inizio trasformazione)
125°C
15
Qi (Q)e
 2Q 2
sin rQdQ
3,45
3,40
Transformation finish
3,35
5
r (Å)
differential RDF
10
0
Transformation start
3,30
-5
3,25
-10
3,20
-15
100
2
3
4
5
6
7
8
200
300
400
500
600
700
Temperatura (°C)
r (Å )
The analyses of XRD patterns show that positions and shapes of RDF peaks progressively
change as temperature increases: in particular r1 slowly decreases whereas r2 increases.
R. Montanari, A. Varone
HT-XRD measurements
For describing the liquid structure the ratio between average distance r between
the 1st (central position of the 1st RDF peak) and 2nd (central position of the 2nd
RDF peak) nearest neighbour atoms is of particular relevance and .
1,65
P1 (Ǻ)
P2(Ǻ)
P2/P1
1,60
126
3.38
4.76
1.41
1,55
350
3.41
5.17
1.52
560
3.26
5.00
1.53
r2 / r1
T(°C)
1,50
1,45
1,40
719
3.24
5.18
1.61
100
200
300
400
500
Temperatura (°C)
P2/P1
1.41
R. Montanari, A. Varone
1.61
600
700
800
Model
Icosahedron and cuboctahedron are related polyhedra that can be built up from the
octahedron that has 12 edges.
If atoms occupy the central position of each edge they form the vertexes of a
cuboctahedron, if atoms occupy the positions dividing the edge in the golden ratio,
i.e. (1/1.618)a = 0.61a , they form the vertexes of an icosahedron. Therefore, if they
are arranged in intermediate positions between 0.5a e (1/1.618)a a intermediate
configuration is obtained.
R. Montanari, A. Varone
Surface Analysis : ELETTRA synchrotron (Trieste)
XPS and SPEM measurements
The SPEM experiments were financially
supported by ELETTRA synchrotron project n.
20120196 and n. 20130335.
The SPEM technique was employed because of
its high lateral resolution (below 50 nm)
Study if the transformations occurring in the
liquid state involve the clustering of alloying
elements.
S. K. Balijepalli, S. Kaciulis, A. Mezzi, R. Montanari, A. Varone, M. Amati
Surface Analysis :
SPEM measurements
Maps (13 × 13 μm2) of Pb/Bi
intensity ratio for the alloy quenched
at 401 °C.
Pb and Bi are strongly clustered after melting, and the size and composition of the clusters
evolve as temperature increases.
The cluster evolution could be due to diffusion processes between clusters and matrix, leading
to the progressive disgregation of clusters and to the homogenization of the liquid alloy
S. K. Balijepalli, S. Kaciulis, A. Mezzi, R. Montanari, A. Varone, M. Amati
G. Barbieri, M. Cesaroni
Summary
Main proprieties of 9 Cr 1 Mo V, Nb modified steel (P91)
Greater strength, that permits increased safety margins in existing units
Significant longer component life under given creep and fatigue loads
Reduced wall thickness for components for the same condition that permit to reduce thermal
stress.
Welding aspects
2/ 3 different chemical compositions of material:
Base Material, filler material, Fused zone in function of the dilution ratio.
Correct time and Temperature for PWHT , pre heating and interpass Temperature
Comparison with Standard Manual practices GTAW+SMAW
Main welding aspects investigated
Influence of low and high speed of welding;
Influence of ratio and mode of deposition;
Influence of PWHT in terms of holding Time and tempering Temperature;
Target
Review of the RCC-MR specifications for welding consumables, welding
processes and related base metal.
Base & Filler Materials
BASE MATERIAL
 Samples to weld come from INDUSTEEL plate
(140 mm thickness)
 Austenitizing (1071°C / 4h08), water cooling,
tempered (757°C / 5h31)
 Hardness measurement (207 HV1)
The thinner 9Cr1MoVNb plate was not originally design
for nuclear and its then not fully compliant with RCCMR(x) recommendation (Ni content).
FILLER MATERIAL
 Böhler welding,Thermanit MTS3,Stick Electrode,
filler wire ( 1,2 mm)
C
Si
Mn
Industeel
0.099
0.216
0.405
BM
RCC-MR
2007
(RM2431.31)
0.0800.120
0.200.50
0.300.60
FM
Böhler
0.109
0.22
0.77
P
S
0.00 0.00
7
2
Cr
Mo
Ni
Al
Nb
V
N
Cu
0.05
4
8.305
0.951 0.13 0.011 0.075
0.201
0.034
Max Max
0.02 0.00
0
5
8.009.50
Max
0.85- Max
0.04
1.05 0.20
0
0.060.10
0.180.25
0.0300.070
Max
0.10
0.00 0.00
6
2
9.03
0.98
0.059
0.196
0.041
0.03
0.46
-
Welding of P91
Were made test provided on the site about manual practices and mechanized TIG
with 60 ° and 75 ° V angle to face Butt Join 12 mm (horizontal position) ;
•Standard Manual procedure (1st pas TIG + filling SMAW);
 Welding of 4 coupons (2 with 60 ° chamfer and 2 with 75° chamfer)
 Influence of 2 PWHT
 Qualification specimens
• GTAW process:
It has been defined the first test matrix for optimizing the welding speed and wire speed for string or
weave beads for automated TIG
 Welding of 4 coupons (4 with 60 ° chamfer and 4 with 75° chamfer an different Deposition Ratio)
 Influence of 2 PWHT
 Qualification specimens
Qualification tests planned after PWHT:
Transverse tensile tests at room temperature
Longitudinal tensile tests at room temperature and 550°C.
Charpy tests for DBTT on FZ;
Metallurgical examination.
Fimec
PWHT time and temperature and
deposition mode
Typical thermal cycle for welding P91
The weave deposition techniques seams
to guaranty better toughness than
stringer beads;
Courtesy of Bhöler
SMAW
Welding SMAW parameter
String beads 160-260
Average SMAW
 Ws=165 cm/min
 DR1=1,27 g/cm
 HI=1,18 KJ/cm
Average GTAW
 Ws= 75 cm/min
 DR= 1,15 g/min
 HI=1,66 KJ/cm
Weave beads 175-275
Average SMAW
 Ws=137 cm/min
 DR2=1,83 g/cm
 HI=1,48 KJ/cm
Average GTAW
 WS= 63 cm/min
 DR= 1,12 g/min
 HI=1,90 KJ/cm
Mechanized GTAW
MB
Mode
LDR
I
V
Ws
[mm/min]
Wfs
HI
DR
[mm/min] [kJ/mm] [g/cm]
230
12
120
660
1,38
0,34
230
13
120
660
1,50
0,34
230
11,3
120
1750
1,30
0,89
230
12,4
120
1750
1,43
0,89
250
13,5
144
1980
1,41
0,84
250
13
144
1980
1,35
0,84
250
12
120
1980
1,50
1,01
250
12,5
120
1980
1,56
1,01
Transizione
FZ
LDR
2h
LDR
4h
TDR
HDR
Welding GTAW parameter
TRD
2h
TRD
4h
V 75 gap 1 TDR
V 60 gap 1 TDR
The as-tempered microstructure consists of a fine prior
austenite grains containing a lath-like tempered
martensite structure with a high dislocation density that is
stabilized by M23C6 carbides and MX(Nb,V) carbonitrides.
Dimensions of the re-affected and not re-affected µsctruttures increase with the deposition rate
SMAW
RCC
RCC
The 4 h PWTH reduce RM in FZ
No sample meets the
requirements (RCC-MR)
4500
BM
ZTA
Saldatura
4000
3500
Pressione (MPa)
The 4 h PWTH reduce HV in FZ
3000
2500
2000
1500
Rp (MPa)
1000
BM (PWHT2)
545
ZTA
580
Saldatura
617
500
RCC
0
0,0
DR2_FZ 275 > 60 J (RCC-MR)
0,1
0,2
0,3
0,4
Profondità di penetrazione (mm)
Corrispondence beetween
Fimec and Tensile Test
0,5
0,6
GTAW
Problem of Cracking IV
Coupling “Target”
Influence of PWHT
The holding time of the PWHT influence the
Hardness of the welds:
The hardness increase from the cap to the rood due to the different dilution ratio
and filler material (Electrode /wire Thermanit MTS3);
The hardness is reduced by increasing of the PWHT holding time ( 2h4)
Mechanical Features
The tensile strength in BM decrease with PWHT;
The RP0,2 & RM on FZ decrease if the holding time of PWHT is increased;
The A% on FZ is less of the 20 %, The V60 with low DR and Low HI allow to
obtain the higher value
THANK YOU