Void Formation and Helium Effects in 9Cr-1MoVNb and 12Cr-1MoVW Steels Irradiated in HFIR and FFTF at 400°C

    Published: Jan 1990

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    Martensitic/ferritic 9Cr-1MoVNb and 12Cr-1MoVW steels doped with up to 2 wt% nickel have up to 450 appm helium after High Flux Isotope Reactor (HFIR) irradiation to ̃38 dpa, but only 5 appm helium after 47 dpa in Fast Flux Test Facility (FFTF). No fine helium bubbles and few or no larger voids were observable in any of these steels after FFTF irradiation at 407°C. By contrast, many voids were found in the undoped steels (30 to 90 appm helium) irradiated in HFIR at 400°C, while voids plus many more fine helium bubbles were found in the nickel doped steels (400 to 450 appm helium). Irradiation in both reactors at ̃400°C produced significant changes in the as-tempered lath/subgrain boundary, dislocation, and precipitation structures that were sensitive to alloy composition, including doping with nickel. However, for each specific alloy the irradiation-produced changes were exactly the same comparing samples irradiated in FFTF and HFIR. particularly the nickel-doped steels. Therefore, the increased void formation appears solely due to the increased helium generation found in HFIR. While the levels of void swelling are relatively low after 37 to 39 dpa in HFIR (0.1 to 0.4%), details of the microstructural evolution suggest that void nucleation is still progressing, and swelling could increase with dose. The effect of helium on void swelling remains a valid concern for fusion application that requires higher dose experiments.


    martensitic/ferritic steels, helium, nickel doping, voids, bubbles, precipitation, M, 23, C, 6, M, 6, C, MC, lath/subgrain boundary structure, neutron irradiation, fusion

    Author Information:

    Maziasz, PJ
    Research staff member II and senior staff member, Oak Ridge National Laboratory, Oak Ridge, TN

    Klueh, RL
    Research staff member II and senior staff member, Oak Ridge National Laboratory, Oak Ridge, TN

    Committee/Subcommittee: E10.02

    DOI: 10.1520/STP24631S

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