STP770: Cumulation of High-Temperature Low-Cycle Fatigue Damage in Two-Temperature Tests

    Reuchet, J
    Centre des Matériaux de l'Ecole des Mines de Paris, Evry,

    Réger, M.
    Centre des Matériaux de l'Ecole des Mines de Paris, Evry,

    Rezai-Aria, F
    Centre des Matériaux de l'Ecole des Mines de Paris, Evry,

    Rémy, L
    Centre des Matériaux de l'Ecole des Mines de Paris, Evry,

    Pages: 18    Published: Jan 1982


    Abstract

    The cumulation of damage in high-temperature low-cycle fatigue is investigated for a cast cobalt-base superalloy MarM509, by using two-temperature testing. The two temperature levels [600 and 900°C (873 and 1173 K)] are taken as representative of low and high temperature behavior. At low temperatures crack initiation is crystallographic, while at high temperatures MC carbides are preferentially oxidized, giving rise to early initiation. Testing is conducted at a constant plastic strain range (Δεp/2 = 0.2 percent), and the remaining fatigue life is determined at one temperature after cycling at the other temperature for a definite amount of the expected life. The fatigue lives so obtained exhibit a large deviation from Miner's rule, particularly when the first cycling is carried out at the higher temperature. A detailed metallographic study using a replication technique shows that this deviation was related to the differences in the microcracking process at each temperature. More quantitatively, an estimate of the life to initiation is defined using a potential drop technique, which has shown that conservative predictions can be made from the application of Miner's rule to the initiation period.

    Keywords:

    high-temperature low-cycle fatigue, cobalt-base superalloy, cumulative damage rules, crack initiation


    Paper ID: STP32429S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP32429S


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