progress on low activation structural steels recent results on nanostructured ferritic alloys...
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PROGRESS ON LOW ACTIVATION STRUCTURAL STEELS
RECENT RESULTS ON NANOSTRUCTURED FERRITIC ALLOYS
A.F.ROWCLIFFE (ORNL)
ARIES PROJECT MEETINGU.C.S.D.
Jan 22nd. – Jan 23rd 2013
Nanograin structure & high density of nanoclusters. High energy mechanical alloying plus high power consolidation Very large interfacial area (NC-matrix and grain boundaries) enhances
recombination of point defects as well as accommodation of helium atoms or bubbles in irradiation.
In ferritic phase, the nanograins & NCs are exceptionally stable up to very high temperatures.
Nanostructured Ferritic Alloys (NFAs)
<Grain size> = 136 (+/- 14) nm
BF-TEM of 14YWT SM10 HeatNv = 1-7 x 1023 m-3 <r> = 1.8 (+/- 0.4) nm
HR-TEM
2
NFAs have outstanding strength and creep properties
M.A.Sokolov, D.T.Hoelzer, L.Tan (ORNL)
12YWT: First discovery of NC by 3DAP in 1999 (ORNL)
MA957: Patented by INCO (1978); NC discovered by 3-DAP in 2003 (ORNL)
14YWT: Developed at ORNL; initial project started in 2001
• MA957 and 12YWT are not commercially available- 12YWT was produced only
once as a small heat by Kobe Steel, Ltd.
- Production of MA957 was discontinued by INCO
Temperature, oC
0 100 200 300 400 500 600 700 800 900
Yie
ld S
tren
gth
, M
Pa
0
300
600
900
1200
1500
1800
12YWT9Cr-2WVTa14YWT-SM614YWT-SM10PM2000MA95714YWT-SM7F82H
FRACTURE TOUGHNESS-STRENGTH PROPERTIES
• UNIQUE NANO-SCALE MICROSTRUCTURE OF THE LOW ACTIVATION NFA 14YWT CHALLENGES THE HIGH STRENGTH-LOW TOUGHNESS PARADIGM FOR STRUCTURAL ALLOYS
D.T.Hoelzer ORNL, unpublished work
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 400 800 1200 1600 2000 2400
14YWT
7000 Series Al Alloy
Multi-phase Nb Alloy
Zr BMG
Super Bainite Steel
AF1410
Fra
ctu
re T
ou
ghn
ess /
T
(MP
am
1/2/K
)
max
(MPa)
Neutron irradiation of 14YWT and 14WT at 300oC, 580oC, and 670oC to ~1.5 dpa (HFIR Rabbit capsules)
-200 -100 0 100 200 300 400 500 600 700
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
14YWT (unirradiated) 14WT (unirradiated)
14YWT (Tirr
=300oC) 14WT (Tirr
=300oC)
14YWT (Tirr
=580oC) 14WT (Tirr
=580oC)
14YWT (Tirr
=670oC) 14WT (Tirr
=670oC)
Str
ess
[MP
a]
Temperature [C]
Irradiated Yield Stress
D.A. McClintock et al., JNM 386-388 (2009)
No DBTT shift was observed in 14YWT after irradiation at 300oC to ~ 1.5 dpa compared to 85oC
shift in Eurofer-ODS
-250 -200 -150 -100 -50 0 50 100 150 200 250 30025
50
75
100
125
150
175
200
14YWT [KJc(1T)
] (unirradiated)
14YWT [KJIc
] (unirradiated)
14YWT [KJc(1T)
] (Tirr
= 300oC)
14YWT [KJIc
] (Tirr
= 300oC)Fra
ctur
e T
ough
ness
[M
Pa
m]
Temperature [C]
Irradiated 14YWT Fracture Toughness
D.A. McClintock, et al., JNM 392 (2009)
Eurofer-ODS
HELIUM MANAGEMENT IN ADVANCED STRUCTURAL ALLOYS
• TEM images of Eurofer 97 (TMS), (a, b), and MA957 (NFA) (c,d)• Neutron irradiated to 25dpa at 500C and simultaneously implanted with
~1450 appm He• G.R.Odette et al., Fusion Materials Semi-Annual Report, DOE/ER-0313/51
HELIUM MANAGEMENT IN ADVANCED STRUCTURAL ALLOYS
• High helium content (1450appm) promotes the formation of a large population of voids in neutron irradiated Eurofer 97
• Same quantity of helium is trapped by ~2nm clusters/particles in MA957 with no void formation
• Swelling rate theory extrapolations indicate that NFA will remain damage-tolerant to much higher levels of dpa and helium
• Extrapolations for the TMS indicate continuing growth of voids with eventual transition to a linear (with dose) swelling regime
NFAs WITH IMPROVED FRACTURE RESISTANCE
• NFAs based on 12-14% Cr tend to exhibit reduced grain boundary fracture resistance with increasing temperature > 400C
• New approaches to NFA fabrication involve controlled phase transformation during high temperature rolling to strengthen grain boundaries while retaining the nano-scale microstructure for high strength and radiation damage resistance
• New compositions are based on Fe-9Cr-2W-0.4Ti-0.2V- 0.3 Y2O3
• Initial results from a joint ORNL-KAERI project funded by Office of Nuclear Science and Technology show promise.
MICROSTRUCTURE OF NEW NFAs
T.S.Byun,D.T.Hoelzer (ORNL), J.H.Koon (KAERI); unpublished work10
9YWTV-PM2Fe-9Cr-2W-0.4Ti-0.2V-0.05C+0.3Y2O3
9YWTV-PM1Fe-9Cr-2W-0.4Ti-0.2V-0.12C-0.3Y2O3
PM1PM2
Strength & Ductility of 9Cr NFAs
• New base NFAs retain YS higher than 500 MPa at 700°C.• Improved ductility for both new NFAs compared to 14YWT
T.S.Byun, D.T.Hoelzer (ORNL), J.H.Koon (KAERI); unpublished work 11
12
Effect of Controlled Rolling 9YWTV-PM on High Temperature Fracture Resistance
T.S.Byun, D.T.Hoelzer ( ORNL ), J.H.Koon (KAERI); unpublished work
• Improvement of fracture toughness in controlled rolled 9YWTV-PM2 is significant.
• The 9YWTV-PM2 controlled rolled at 900°C for 50% reduction resulted in the best fracture toughness among NFAs, which is as high as those of non-ODS F/M steels.
• Potential avenue for NFAs based on 9Cr with improved high temperature fracture resistance
0
50
100
150
200
250
300
350
400
450
22000 24000 26000 28000 30000 32000 34000 36000
NFA 12YWTNFA MA9579Cr-WMoVNb SteelNFA 14YWT
LMP T(K)[25 + log10t(h)]
Str
ess
(MP
a)
900°C, 1104h
800°C, 14235h
800°C, 817h
650°C, 13000h
600°C, 17000h
650°C, 1080h650°C
16h
650°C>72h
825°C, 57600h(in test)
800°C, 38555h
800°C, 16584h(in test)
Creep performance of NFAs
• Creep test on ruptured MA957 started in Oct., 2003 (INE
• Creep test on 14YWT-SM10 started in April, 2008
• Klueh et al, J. Nucl. Mat., (2005)• I-NERI FY01-04
-1.000
0.000
1.000
2.000
3.000
4.000
5.000
6.000
7.000
0 10000 20000 30000 40000 50000
CR
EE
P S
TR
AIN
(%
)
TIME (HOURS)
Ruptured after ~38,555 h