STP1297

    Environmentally Enhanced Crack Growth in Nickel-Based Alloys at Elevated Temperatures

    Published: Jan 1997


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    Abstract

    A recent understanding of environmentally enhanced sustained-load crack growth in nickel-based superalloys at elevated temperatures is presented. This understanding is based on the results of coordinated studies of crack growth kinetics, surface chemistry, and microstructure in a commercial Inconel 718. The results suggest that environmental enhancement of sustained-load crack growth in Inconel 718 is associated with the formation and rupture of niobium oxides at grain boundary surfaces and is controlled mainly by the rate of oxidation and decomposition of niobium carbides at the grain boundaries. Data on other nickel-based alloys in the literature appear to support this suggested role of niobium. Initial results from a study of a niobium-free Ni-18Cr-18Fe alloy (its base composition is identical to Inconel 718) confirm the possible influence of niobium and the proposed mechanism. Some open issues for further investigation are discussed.

    Keywords:

    environmentally enhanced crack growth, elevated temperature crack growth, sustained-load crack growth, environmental effect, effect of oxygen, effect of water vapor, oxidation, role of niobium


    Author Information:

    Gao, M
    Principal research scientist, graduate student, research scientist, and professor, Lehigh University, Bethlehem, PA

    Chen, S-F
    Principal research scientist, graduate student, research scientist, and professor, Lehigh University, Bethlehem, PA

    Chen, GS
    Principal research scientist, graduate student, research scientist, and professor, Lehigh University, Bethlehem, PA

    Wei, RP
    Principal research scientist, graduate student, research scientist, and professor, Lehigh University, Bethlehem, PA


    Paper ID: STP16318S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP16318S


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