STP945

    Elevated Temperature Fatigue Crack Growth of Single Crystal René N4 Superalloy

    Published: Jan 1988


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    Abstract

    Constant-load-amplitude fatigue crack growth tests were conducted at 0.33 Hz over a temperature range of 538 to 871°C for single crystal René N4 nickel base superalloy. Crack growth behavior was found to be similar in the Paris law regime for the entire temperature range tested except for a slight increase in growth rate at 871°C at higher levels of the stress intensity range. Mainly, two distinct modes of fatigue fracture were observed, namely, a flat, featureless, Stage II fracture morphology and a faceted, crystallographic, Stage I cracking mode. The Stage II fatigue fracture occurred over the entire range of ΔK at the three highest temperatures. At 538°C, however, a transition from Stage II to Stage I fatigue fracture occurred with increase in ΔK. The higher crack growth rates at higher temperatures in the high-stress-intensity range were attributed to casting defects present in the material.

    Keywords:

    fatigue crack growth, single crystal, nickel base superalloy, elevated temperature, fractography, fracture mechanism


    Author Information:

    Venkataraman, S
    Resident NRC research associate and senior scientist, AFWAL MLLN, Wright-Patterson Air Force Base, OH

    Nicolas, T
    Resident NRC research associate and senior scientist, AFWAL MLLN, Wright-Patterson Air Force Base, OH

    Khobaib, M
    Research scientist, University of Dayton Research Institute, Dayton, OH


    Paper ID: STP23274S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP23274S


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