STP1372

    Mean Stress and Environmental Effects on Near-Threshold Fatigue Crack Propagation on a Ti6246 Alloy at Room Temperature and 500°C

    Published: Jan 2000


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    Abstract

    The cracking behavior of a Ti6246 alloy under cyclic loading superimposed to different levels of mean stress is studied, with special attention to the near-threshold fatigue crack propagation regime, and to possible coupled effects of corrosion and creep. Tests were conducted at room temperature and 500°C in selected environmental conditions (high vacuum, controlled atmospheric leak low pressure, controlled partial pressure of water vapor in pure argon) and at different frequencies. The near-threshold crack propagation at low Kmax (i.e. low R ratio) is shown to be highly sensitive to the environment, and a predominant detrimental influence of water vapor is observed, even under very low partial pressure. Conditions for the occurrence of an abnormal behavior consisting in the disappearance of the threshold for sufficiently high Kmax level, are discussed from tests performed at various constant Kmax levels in ambient air, high vacuum and humidified argon. This effect is observed in air and in vacuum for Kmax higher than 52 MPa√m, and is related to an intrinsic creep damage process which appears more efficient at room temperature than at 500°C and more accentuated in air than in vacuum. The origin of this abnormal near-threshold behavior is discussed in comparison with a similar behavior described in the literature at room temperature on another type of Ti6246 alloy and at 120°C on an IMI834. Additional experiments conducted at 500°C in humidified argon have shown a critical Kmax level reduced to 22 MPa√m. This behavior is suspected to be related to a contribution of stress corrosion cracking induced by water vapor when some conditions favoring a localization of the deformation and the attainment of a critical embrittlement are fulfilled.

    Keywords:

    fatigue, titanium alloys, environment, corrosion, temperature, mean stress crack propagation threshold


    Author Information:

    Sarrazin-Baudoux, C
    Chargée de Recherche CNRS, Research scientist, Directeur de Recherche CNRS, Laboratoire de Mécanique et de Physique des Matériaux — UMR CNRS n° 6617 ENSMA, Chasseneuil de Poitou,

    Chabanne, Y
    Chargée de Recherche CNRS, Research scientist, Directeur de Recherche CNRS, Laboratoire de Mécanique et de Physique des Matériaux — UMR CNRS n° 6617 ENSMA, Chasseneuil de Poitou,

    Petit, J
    Chargée de Recherche CNRS, Research scientist, Directeur de Recherche CNRS, Laboratoire de Mécanique et de Physique des Matériaux — UMR CNRS n° 6617 ENSMA, Chasseneuil de Poitou,


    Paper ID: STP13442S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP13442S


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