Recent Progress on Ferritic Alloys Recent Progress on Ferritic Alloys for Fusion Structural Applicationsfor Fusion Structural Applications

R.J Kurtz1 & U.S. Fusion Materials Scientists

1Pacific Northwest National Laboratory

Fusion Nuclear Science & Technology MeetingAugust 18 – 20, 2009University of California Los Angeles

Irradiation Hardening of Eurofer97 at Irradiation Hardening of Eurofer97 at 300 - 336°C300 - 336°C

€

Δσ =Δσys 1−exp−dpadpa0( )[ ]p

€

k=Δσys / dpa0

0

100

200

300

400

500

600

700

0 10 20 30 40 50 60 70 80

E97-1, 300°CE97-2, 300°C325°C330°C332°C336°C

, Dose dpa

300° Fit to C data only

Fit to all data

Hardening coefficient:

Lucon & Vandermeulen / SCK•CEN-BLG-1042 Rev.(1) (2007)

-100

0

100

200

300

400

500

0 100 200 300 400 500 600

Spaetig et al. / ICFRM-13

Rensman, ICFRM-13

Lucon & Vandermeulen

Yamamoto et al. / JNM 2006

Ttest

= Tirr

, °C

Protons

The observation of a shape invariant master KJc(T-To) curve (MC) allows efficient fracture testing in the cleavage transition with a limited number of small specimens.

ΔTo = ΔTirr + ΔTdyn + ΔTstruc + Δtmarg

Requires size and geometry adjustments for constraint loss and statistical size effects - new methods are being developed.

T(ºC)T

o(1) T

o(2)

T-To(ºC)0

Kor

c.

0

100

200

300

400

500

-200 -150 -100 -50 0 50 100 150T - T

o (ºC)

a.

Master Curve and Small SpecimensMaster Curve and Small Specimens

Impact of He-Rich Environment on Impact of He-Rich Environment on Neutron Irradiated MaterialsNeutron Irradiated Materials

A unique aspect of the DT fusion environment is substantial production of gaseous transmutants such as He and H.

Accumulation of He can have major consequences for the integrity of fusion structures such as:

− Loss of high-temperature creep strength.

− Increased swelling and irradiation creep at intermediate temperatures.

− Potential for loss of ductility and fracture toughness at low temperatures.

Grain boundary

1

10

100

1000

Un-implanted 200 appm He

Schroeder and Batflasky, 1983

0

50

100

150

200

250

300

0 100 200 300 400

Δσy ( )MPa

ΔT0 = 0.58 Δσ

y

F82H (IEA)T

irr = 250 ~ 300 ºC

c.

Relation Between Relation Between ΔΔTToo and and ΔσΔσyy for for F82H and Effect of High HeF82H and Effect of High He

Yamamoto et al. / Journal of Nuclear Materials 356 (2006) 27.

Ductile-to-Brittle Transition Ductile-to-Brittle Transition Temperature Shifts – Effect of HeTemperature Shifts – Effect of He

Ductile

Brittle

T. Yamamoto, Y. Dai, G.R. Odette, et al, Trans. American Nuclear Society 98 (2008) 1111.

€

ΔTc

€

ΔTc =CcΔσ y =CcΔσ ys 1− exp −dpa −dpa0( )[ ]1

2

€

Cc = 0.4 He < 500

Cc = 0.4 + 0.0007(He − 500) 500 < He < 1500

Cc =1.1°C/MPa He > 1500

0

200

400

600

800

1000

0 50 100 150 200dpa

neutron only

10 ( / )appmHe dpa

Cc ≤ 1.1

Fusion Reactor Conditions

0

50

100

150

200

250

300

350

400

450

22000 24000 26000 28000 30000 32000 34000 36000

NFA 12YWT

NFA MA957

9Cr-WMoVNb Steel

LMP T(K)[25 + log10t(h)]

Str

ess

(M

Pa)

900°C, 1104h

800°C, 14235h

800°C, 817h

650°C, 13000h

600°C, 17000h

650°C, 1080h650°C16h

650°C>72h

825°C, 39024h(in test)

800°C, 38555h(failed recently)

Thermal Creep of NFAs: MA957 and Thermal Creep of NFAs: MA957 and 12YWT12YWT

D.T. Hoelzer, et al 2008

G.R. Odette, et al 2008

NFA = Nanocomposited ferritic alloy

Fe – (12-14)Cr – Ti – Y2O3

• Remarkable thermal stability @ ≥ 1150°C:

r(ta,Ta) - ro ≈ ro[2.4x1027exp(-880x103/RT) - 1]1/5

• Minor softening 104 h @1000°C

0

1

2

3

4

5

6

7

1100 1150 1200 1250 1300 1350 1400 1450

Temperature (oC)

9 Hour MA957 Anneal

1

AE Aged

Aged

20nm

AE

0

50

100

150

200

250

300

350

0 2000 4000 6000 8000 1 104 1.2 104

800°C850°C900°C950°C1000°C

Aging Time (h)

1000°C, 11 kh

Y-Ti-O Nanocluster Thermal StabilityY-Ti-O Nanocluster Thermal Stability

No DBTT Shift Observed in 14YWT No DBTT Shift Observed in 14YWT After Irradiation at 300After Irradiation at 300ooC to ~1.5 dpaC to ~1.5 dpa

D.A. McClintock et al., ICFRM-13C. Petersen et al., 2005

He Bubble Distribution in Irradiated He Bubble Distribution in Irradiated F82H mod.3 (500F82H mod.3 (500°C, 9 dpa, 380 appm He)°C, 9 dpa, 380 appm He)

He bubbles observed throughout foil, found on low angle boundaries and precipitate interfaces

Slightly broader size range, from 0.5 to ~7 nm Density is ~1.0 x 1023 m-3, avg. size is 1.7

G.R. Odette, P. Miao, T. Yamamoto, et al, Trans. American Nuclear Society 98 (2008) 1148.

He Bubble Distribution in Irradiated He Bubble Distribution in Irradiated MA957 CW (500MA957 CW (500°C, 9 dpa, 380 appm He)°C, 9 dpa, 380 appm He)

He bubbles observed throughout foil, narrow size distribution of small bubbles forming on Y-Ti-O nano-features.

Boundaries appear to be protected from bubble formation Density is ~3 x 1023 m-3, avg. size is ~1 nm

G.R. Odette, P. Miao, T. Yamamoto, et al, Trans. American Nuclear Society 98 (2008) 1148.

Helium Bubble Size and Number Helium Bubble Size and Number Density at 500°C, 380 appm He/9 dpaDensity at 500°C, 380 appm He/9 dpa

MA957

F82H Eurofer97

•Grain aspect ratio ranges from 5:1 to 10:1•Extrusion direction strong but brittle.

0

50

100

150

-200 -100 0 100 200

LR

LR(ductile)

CL

CL(ductile)

T (ºC)

Grain Aspect RatioGrain Aspect Ratio

Low-temperature fracture toughness• ODS alloys are known to have high DBTT and low upper shelf energy – strengthening by

nanoclusters may exacerbate this problem.• Reduce anisotropic properties associated with high texture or GAR.

Joining• Historically a significant problem with ODS alloys, but maybe more difficult due to the

structure of the nanoclusters.• Friction stir welding shows potential.

• Stability of nanoclusters during irradiation (nuclear applications)• Most studies are based on ODS ferritic alloys containing coarser oxide phases, not

nanoclusters.• Little or no information on structural stability of nanoclusters (creep properties, enhancing

recombination of point defects, or He management.

Critical Issus for NFA - ICritical Issus for NFA - I

Scale-up technology• Current knowledge of processing conditions and reproducibility of several small

heats of 14YWT favor scale-up to larger heats.• Must partner with industry.• Fabrication experience for NFA is not extensive.

Cost• Modifications in the mechanical alloying approach.• Alternative processing to mechanical alloying – thermo-mechanical treatment

approaches preferable.

Critical Issus for NFA - IICritical Issus for NFA - II