1. Recent Progress on Ferritic Alloys for Fusion Structural Applications R.J Kurtz 1 & U.S. Fusion Materials Scientists 1 Pacific Northwest National Laboratory Fusion Nuclear Science & Technology Meeting August 18 – 20, 2009 University of California Los Angeles

2. Irradiation Hardening of Eurofer97 at 300 - 336°C Hardening coefficient: Lucon & Vandermeulen / SCKCEN- BLG-1042 Rev.(1) (2007)

3.  The observation of a shape invariant master K Jc (T-T o ) curve (MC) allows efficient fracture testing in the cleavage transition with a limited number of small specimens.  T o =  T irr +  T dyn +  T struc +  t marg  Requires size and geometry adjustments for constraint loss and statistical size effects - new methods are being developed. c. a. Master Curve and Small Specimens

4. Impact of He-Rich Environment on Neutron 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 Schroeder and Batflasky, 1983

5. c. Relation Between  T o and  y for F82H and Effect of High He Yamamoto et al. / Journal of Nuclear Materials 356 (2006) 27.

6. Ductile-to-Brittle Transition Temperature Shifts – Effect of He Ductile Brittle T. Yamamoto, Y. Dai, G.R. Odette, et al, Trans. American Nuclear Society 98 (2008) 1111. Fusion Reactor Conditions

7. Thermal Creep of NFAs: MA957 and 12YWT D.T. Hoelzer, et al 2008 G.R. Odette, et al 2008 NFA = Nanocomposited ferritic alloy Fe – (12-14)Cr – Ti – Y 2 O 3

8. Remarkable thermal stability @ ≥ 1150°C: r(t a,T a ) - r o ≈ r o [2.4x10 27 exp(-880x10 3 /RT) - 1] 1/5 Minor softening 10 4 h @1000°C 11 AE Aged 20nm AE 1000°C, 11 kh Y-Ti-O Nanocluster Thermal Stability

9. No DBTT Shift Observed in 14YWT After Irradiation at 300 o C to ~1.5 dpa D.A. McClintock et al., ICFRM-13C. Petersen et al., 2005

10. He Bubble Distribution in Irradiated F82H mod.3 (500°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 10 23 m -3, avg. size is 1.7 G.R. Odette, P. Miao, T. Yamamoto, et al, Trans. American Nuclear Society 98 (2008) 1148.

11. He Bubble Distribution in Irradiated MA957 CW (500°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 10 23 m -3, avg. size is ~1 nm G.R. Odette, P. Miao, T. Yamamoto, et al, Trans. American Nuclear Society 98 (2008) 1148.

12. Helium Bubble Size and Number Density at 500°C, 380 appm He/9 dpa MA957 F82H Eurofer97

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

14.  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 - I

15.  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 - II