t. hirai, m. batilliot, j. linke, g. pintsuk forschungszentrum jülich, euratom association, jülich
DESCRIPTION
Cracking of a tungsten material exposed to single pulse thermal shock loads at elevated temperatures. T. Hirai, M. Batilliot, J. Linke, G. Pintsuk Forschungszentrum Jülich, Euratom Association, Jülich. Outline (1) Motivation (2) Thermal shock tests in electron beam facility JUDITH - PowerPoint PPT PresentationTRANSCRIPT
Mem
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Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ
Cracking of a tungsten material exposed to single pulse thermal shock loads at elevated temperaturesT. Hirai, M. Batilliot, J. Linke, G. PintsukForschungszentrum Jülich, Euratom Association, Jülich
Outline(1) Motivation(2) Thermal shock tests in electron beam facility JUDITH(3) Results: Cracking of tungsten(4) Summary
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 2
1 mm1 mm
T0 = RT weight loss = 0.5 mg T0 = 650 - 700°C weight loss = 4.0 mg
Einc = 2.3 MJm-2, t = 1.8 ms, (Pins = 1.3 GW/m2) 10 shots at JEBIS
J. Linke et al., presented in ICFRM-10, Baden Baden Germany 2001.
Cracking and melting of W under thermal shock loads
Thermal shock response of W
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 3
Cracking
Power density
Melting boiling
Thermal load
Cra
ckin
g th
resh
old
Mel
ting
thre
shol
d
Safe operation Crack propagationRe-crystallization
Melting, re-solidification, Irregular shape, Melt-layer loss,boiling
• Melting threshold: related to thermal properties (e.g. Dthermal), melting point (Tm)• Cracking threshold: related to thermal properties (e.g. Dthermal, ), mechanical properties, loading conditions (strain rate ~ T./t)
Dthermal: thermal diffusivity,: thermal expansion, t: pulse duration
Thermal shock loads on metals
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 4
Cracking
Power density
Melting
Thermal load(120 keV e-beam)
W: c
a. 5
um
Cra
ckin
g th
resh
old
Mel
ting
thre
shol
d
Safe operation Crack propagationThermal fatigue
Melting, re-solidification
T_(thermal/yield>1)
normalized stress (thermal stress/yield stress) >
1bulk temp. Max surface temp.
Tsurf in thermal shock loadsTm= 3400 oC
DBTT (300 ~ 600 oC depending on strain rate)
bulk temp. Max surface temp.
bulk temp. Max surface temp.bulk temp. Max surface temp.
Thermal shock loads on W materials
Recrystallization
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 5
Aims:• Examine W cracking failure under single pulse by using (i) power density (T) and (ii) bulk temperature (T0) as the parameters• Find safe operation range of the W grade under this condition
Cracking of W materials is important • Cracking threshold is lower than melting threshold• Cracking may cause fatal destruction of brittle materials
Single pulse is advantageous for understanding • Single shot tests: simple to model by original & heat treated material parameters • Multiple shot tests: need to consider dynamic material modification, hardening
W has 4 characteristic temperatures• DBTT; 300 - 600 oC, depending on strain rate• At temperature, thermal stress/yield stress > 1 • Recrystallization temperature ~ 1300 oC• Melting point; 3400 oC
Aims of the work
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 6
Outline
(1) Introduction/Motivation
(2) Thermal shock tests in electron beam facility
(3) Results: Cracking of tungsten
(4) Summary
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 7
Activated samples, Be samplesT <100 GBq as gas, <250 GBq in bulk
HV (<150 kV)
diagnostics:infrared camerapyrometervideo
cathodeElectron gun
x-y deflectioncoils
clampingholder
actively cooled sample
vacuum system:TMP, 2200 l/s
HV (<150 kV)
diagnostics:infrared camerapyrometervideo
cathodeElectron gun
x-y deflectioncoils
clampingholder
actively cooled sample
vacuum system:TMP, 2200 l/s
Electron beam facility, JUDITH, FZJ
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 8
200 8006004000.00
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0.60
0.70
0.80
0.90
0 100 300 500 700 900
Bulk temperature (°C)
Po
wer
den
sity
(G
W.m
-2)
DBTT
T=1697 oC
T= 1131 oC
T= 606 oC
T = 2P.t0.5/(..c.)0.5
A
B
C
Materials and Loading conditions
Loading conditions: Pulse duration 5 ms, single shot, loading area 16 mm2
Materials: ITER-reference W grade, deformed tungsten from PlanseeФ12 mm, 5 mm thickGrain diameter: ~20 µm
ΔT
T0
200 um Hea
t flu
xcross section
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 9
A 0.43 GW/m2, 5ms at 200 oC
W cracking; major cracks, micro-crack network
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 10
B 0.7 GW/m2, 5 ms at 200 oC
W cracking: major cracks, discontinuing cracks
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 11
C 0.43 GW/m2, 5 ms at 600 oC
W cracking: No major cracks, micro-crack network
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 12
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0 200 400 600 800 1000
Starting temperature (°C)
Ab
sorb
ed p
ow
er d
ensi
ty (
GW
.m-2
)
400 µm400 µm400 µm
400 µm400 µm400 µm
400 µm400 µm400 µm400 µm400 µm400 µm
400 µm400 µm400 µm
400 µm400 µm400 µm
200 µm200 µm200 µm
200 µm200 µm200 µm
200 µm200 µm200 µm
200 µm200 µm200 µm
200 µm200 µm200 µm 200 µm200 µm200 µm
200 µm200 µm200 µm
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t)
(MW
.m-2
.s1/2
)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine) Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t)
(MW
.m-2
.s1/2
)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px
sqrt
(t) (
MW
.m-2
.s1/
2)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px
sqrt
(t) (
MW
.m-2
.s1/
2)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px
sqrt
(t) (
MW
.m-2
.s1/
2)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px
sqrt
(t) (
MW
.m-2
.s1/
2)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t)
(MW
.m-2
.s1/2
)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t)
(MW
.m-2
.s1/2
)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t) (M
W.m
-2.s
1/2)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t) (M
W.m
-2.s
1/2)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t)
(MW
.m-2
.s1/2
)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t)
(MW
.m-2
.s1/2
)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
0
10
20
30
40
50
60
70
0 200 400 600 800 1000
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0 200 400 600 800 1000
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70
0 200 400 600 800 1000
0
10
20
30
40
50
60
70
0 200 400 600 800 1000
T= 606 oC
T= 1131 oC
T=1697 oC
Bulk temperature (oC)
Major cracks, microcracks and surface modification
ΔT
T0
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 13
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
0 200 400 600 800 1000
Starting temperature (°C)
Ab
sorb
ed p
ow
er d
ensi
ty (
GW
.m-2
)
400 µm400 µm400 µm
400 µm400 µm400 µm
400 µm400 µm400 µm400 µm400 µm400 µm
400 µm400 µm400 µm
400 µm400 µm400 µm
200 µm200 µm200 µm
200 µm200 µm200 µm
200 µm200 µm200 µm
200 µm200 µm200 µm
200 µm200 µm200 µm 200 µm200 µm200 µm
200 µm200 µm200 µm
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t)
(MW
.m-2
.s1/2
)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine) Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t)
(MW
.m-2
.s1/2
)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px
sqrt
(t) (
MW
.m-2
.s1/
2)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px
sqrt
(t) (
MW
.m-2
.s1/
2)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px
sqrt
(t) (
MW
.m-2
.s1/
2)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px
sqrt
(t) (
MW
.m-2
.s1/
2)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t)
(MW
.m-2
.s1/2
)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t)
(MW
.m-2
.s1/2
)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t) (M
W.m
-2.s
1/2)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t) (M
W.m
-2.s
1/2)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t)
(MW
.m-2
.s1/2
)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
Discontinuing cracks
Low density
High density
Cracks network
No microcracks
Cracks network (wide and fine)
Microcracks
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Temperature (°C)
Px sq
rt(t)
(MW
.m-2
.s1/2
)
Random microcracks
Low density
High density
Grain bondary cracks
No microcracks
Grain boundary cracks(wide and fine)
0
10
20
30
40
50
60
70
0 200 400 600 800 1000
0
10
20
30
40
50
60
70
0 200 400 600 800 1000
0
10
20
30
40
50
60
70
0 200 400 600 800 1000
0
10
20
30
40
50
60
70
0 200 400 600 800 1000
T= 606 oC
T= 1131 oC
T=1697 oC
Bulk temperature (oC)
Major cracks, microcracks and surface modification
No cracks, surface modification
Majo
r cracks
Microcracks
ΔT
T0
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 14
2. Microcracks
1. Major cracks
3. Surface modification
W cracking under single pulse
0.8
0.4
0.6
0.2
0
P [
GW
/m2 ]
T0 [oC]0 200 400 600 800
No cracks, Surface modification
Majo
r cracks
Microcracks
Threshold temperature brittleness of the material below DBTT
Threshold power density thermal stress > yield strength
Only at high temperature recrystallization of surface layer
4. Surface elevation
Safe operation of the W grade
5 ms
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 15
No clear dependence on power density related material constant such as grain size
Crack distance
Mean crack distance
0
50
100
150
200
250
300
0.0 0.2 0.4 0.6 0.8 1.0Absorbed power density (GW.m-2)
Mea
n cr
ack
dist
ance
[µm
]
Power density [MW/m2]
Microcracks at 200 oCMicrocracks at 400 oCMicrocracks at 600 oC
Microcrack networks
No cracks
Discontinuing networks
Thermal expansionCompressive stresses Plastic deformation
ShrinkageGrain boundary opening
heating Cooling
Thermal expansionCompressive stresses Plastic deformation
ShrinkageGrain boundary opening
heating Cooling
No cracksThermal expansionCompressive stresses Plastic deformation
ShrinkageGrain boundary opening
heating Cooling
Thermal expansionCompressive stresses Plastic deformation
ShrinkageGrain boundary opening
heating Cooling
Tensile stresses rupture at G.B.
Microcrack formation1. Plastic deformation at heating phase2. Generation of tensile stress in cooling phase3. Rupture at grain boundary due to the tensile stress
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 16
Mean microcrack width ~ 1 um
Maximum major crack width at 0.4 GW/m2 at 200 oC
Crack width
Mean crack width
0
1
2
3
4
5
6
7
8
0.0 0.2 0.4 0.6 0.8 1.0
Absorbed power density (GW.m-2)
Cra
ck w
idth
[µm
]
Power density [MW/m2]
Major cracks at 200 °C Microcracks at 200 °CMicrocracks at 400 °CMicrocracks at 600 °C
0.4 GW/m2 5 ms 200oC
Major cracks
Microcracks
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 17
Maximum elevation at 0.4 GW/m2 at 200 oC; same tendency as the crack widthContribution plastic deformation, extending to the free surface
Maximum at 200oC and decease at higher temperatures Contribution from thermal vacancies is not dominant
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.00 0.20 0.40 0.60 0.80 1.00Absorbed power density (GW.m-2)
Hei
gh
t (µ
m)
200 °C 400 °C 600 °C 800 °C
Height
Surface elevation height
0.4 GW/m2 5 ms 200oC
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 18
Outline
(1) Motivation
(2) Thermal shock tests in electron beam facility JUDITH
(3) Results: Cracking of tungsten
(4) Summary
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 19
By using deformed W grade, crack appearance under single pulse thermal shock tests were studied in the electron beam facility JUDITH.
Two kinds of cracks: (i) major cracks, i.e. large macroscopic cracks running over the loaded area with a low crack density; (ii) microcracks, i.e. cracks appearing between major cracks and often creating a network
Major cracks were caused by brittleness of the material at the temperature
Microcracks were formed by: (1) Plastic deformation at heating phase; (2) Generation of tensile stress in cooling phase; (3) Rupture at grain boundary due to the tensile stress. The less developed micro-crack at high power density due to reduction of elastic modulus at the peak temperature.
Safe operation condition of the grade under 5 ms loads: >200oC, < 0.28 GW/m2
as far as crack initiation is concered
Crack growth rates of those cracks are important and need to be studied (multiple shot thermal shock loads).
Summary
Takeshi Hirai | Institute of Energy Research | Association EURATOM – FZJ26 May 2008 No 20
Thank you for your attention