STP995V1

    Creep Crack Growth of Alloy 800H in Controlled-Impurity Helium

    Published: Jan 1988


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    Abstract

    The creep crack growth behavior of Alloy 800H has been characterized at temperatures of 677C (1250F) and 732C (1350F) in controlled-impurity helium. Cold-worked material in various recrystallized conditions, expected to be encountered in elevated-temperature service, was tested in center-cracked tension specimen form under constant load. The tests were conducted under dominantly steady-state conditions where the estimated transition time to steady-state creep for each test is a small fraction of the total test time. The results indicate that the crack-tip field parameter, C*, as was experimentally measured, is a good descriptive parameter for the steady-state creep crack growth rate of this material. In fact, the crack growth rate, da/dt, versus C* data from all five tests spanning three different material conditions, two temperatures, and three orders of magnitude of crack growth rates appeared to consolidate into a single straight line on a logarithmic plot. The metallographic results show that crack extension occurs dominantly by the intergranular creep camage mechanisms anticipated in service.

    Keywords:

    Alloy 800, Alloy 800H, cold working, creep, crack growth, crack propagation, fracture mechanics, high-temperature fracture, Incoloy 800, Incoloy 800H, recrystallization, nonlinear fracture mechanics


    Author Information:

    Foulds, JR
    Staff engineer, Failure Analysis Associates, Palo,


    Paper ID: STP26773S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP26773S


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