STP1186: Modeling of Thermomechanical Fatigue Damage in Coated Alloys

    Kadioglu, Y
    Research associate and professordirector, National Science FoundationUniversity of Illinois, WashingtonUrbana, DCIL

    Sehitoglu, H
    Research associate and professordirector, National Science FoundationUniversity of Illinois, WashingtonUrbana, DCIL

    Pages: 18    Published: Jan 1993


    Abstract

    A life prediction model that determines the contribution of fatigue, creep and environmental damage to failure was developed for an aluminide coated nickel-based superalloy, Mar-M247. In the first phase of the study, isothermal (IF) and thermomechanical fatigue (TMF) experiments were conducted to investigate the experimental damage mechanisms. In the second phase, an analytical technique was advanced to compute the stress fields due to a surface inclusion in a half-space where the inclusion simulates the oxide spike. The technique is based on Eshelby's equivalent inclusion method and elucidates the mismatch in elastic moduli and thermal expansion coefficients of the matrix and the oxide spike on local strain fields. The fatigue life results of several experiments, along with the local stress-strain field in the vicinity of an oxide spike, were employed to define the model constants. Life prediction bounds are established corresponding to short-time coating protection, where the coating provides inconsiderable protection to substrate, and long-time coating protection, where the coating provides appreciable protection to the substrate. For in-phase loading, since the failure is governed by creep damage, the nature of coating protection did not influence the fatigue lives. The out-of-phase predictions corresponding to short-time coating protection and the experimental data coincided as the maximum temperature increased in the experiments, confirming that the coating provides unsubstantial protection at higher temperatures.

    Keywords:

    thermomechanical fatigue, high temperature, oxidation, nickel-based superalloy, coating, life-prediction, surface inclusion


    Paper ID: STP24247S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP24247S


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