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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. Recent Progress on Ferritic Alloys for Fusion Structural Applications.

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Recent Progress on Ferritic Alloys for Fusion Structural Applications

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  1. R.J Kurtz1 & U.S. Fusion Materials Scientists 1Pacific Northwest National Laboratory Fusion Nuclear Science & Technology Meeting August 18 – 20, 2009 University of California Los Angeles Recent Progress on Ferritic Alloys for Fusion Structural Applications

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

  3. a. c. Master Curve and Small Specimens • 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. DTo = DTirr + DTdyn + DTstruc + Dtmarg • Requires size and geometry adjustments for constraint loss and statistical size effects - new methods are being developed.

  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. Schroeder and Batflasky, 1983 Grain boundary

  5. c. Relation Between To 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 T. Yamamoto, Y. Dai, G.R. Odette, et al, Trans. American Nuclear Society 98 (2008) 1111. Fusion Reactor Conditions Ductile Brittle

  7. Thermal Creep of NFAs: MA957 and 12YWT NFA = Nanocomposited ferritic alloy Fe – (12-14)Cr – Ti – Y2O3 D.T. Hoelzer, et al 2008 G.R. Odette, et al 2008

  8. Aged AE 1m Aged AE 20nm Y-Ti-O Nanocluster Thermal Stability • Remarkable thermal stability @ ≥ 1150°C: r(ta,Ta) - ro ≈ ro[2.4x1027exp(-880x103/RT) - 1]1/5 • Minor softening 104 h @1000°C 1000°C, 11 kh

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

  10. He Bubble Distribution in Irradiated F82H mod.3 (500°C, 9 dpa, 380 appm He) G.R. Odette, P. Miao, T. Yamamoto, et al, Trans. American Nuclear Society 98 (2008) 1148. • 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

  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 1023 m-3, avg. size is ~1 nm G.R. Odette, P. Miao, T. Yamamoto, et al, Trans. American Nuclear Society 98 (2008) 1148.

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

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

  14. Critical Issus for NFA - I • 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.

  15. Critical Issus for NFA - II • 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.

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