STP683

    Fracture Toughness of Irradiated Nimonic PE16 at High Temperatures

    Published: Jan 1979


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    Abstract

    Fracture toughness results are presented for the nickel-base austenitic alloy Nimonic PE16 following hot tension tests on irradiated compact-tension specimens 6.5 mm thick and data analysis using linear elastic and post-yield techniques.

    Postirradiation fracture toughness values decreasing from ∼70 to 10 MNm-3/2 were found between 550 and 800°C for specimens with yield strengths of 380 to 517 MNm-2 after irradiation at ∼500 and 700°C to 4.5 to 10.2 × 1020 (thermal) neutrons (n)/cm-2 and 17- to 24-ppm helium. Below 550°C the specimens failed with gross plastic deformation.

    The deterioration in fracture toughness was attributed to helium bubble growth and coalescence on stressed grain boundaries. This conclusion was supported by the detection of small closely spaced helium bubbles in grain boundaries of an irradiated PE16 tension specimen fractured at 700°C and by estimates of the growth stress, growth kinetics, and fracture strain for the observed bubble morphology.

    The fracture toughness values have been used to calculate critical defect sizes in representative defect geometries comprising a notch in a round bar or a semi-elliptical defect in a plate. For low-toughness material, small critical defect sizes of ∼0.5 mm were found at stress levels between 0.2 and 0.6 of the ultimate tensile strength. These results emphasize the close attention required to proper design, manufacture, and inspection in order to avoid such small defects together with possible limitations to the operation of components in the low-toughness region.

    Keywords:

    neutron irradiation, austenitic alloy, fracture toughness, high temperature, irradiation embrittlement, mechanical properties


    Author Information:

    Nicholson, RD
    Research officer and section leader, Central Electricity Generating Board, Berkeley Nuclear LaboratoriesCentral Electricity Generating Board, Marchwood Engineering Laboratories, BerkeleySouthampton, Gloucestershire

    Jones, RB
    Research officer and section leader, Central Electricity Generating Board, Berkeley Nuclear LaboratoriesCentral Electricity Generating Board, Marchwood Engineering Laboratories, BerkeleySouthampton, Gloucestershire


    Paper ID: STP38186S

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP38186S


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