Creep-Fatigue Interaction Mechanisms in a near-alpha Titanium Alloy at Room Temperature

For over three decades, aeroengine manufacturers are confronted to the phenomenon of room temperature dwell-effect consisting in a decrease in structure life due to the introduction of hold periods at the maximum stress of the pure cyclic loading waveform. Many studies have been conducted to analyze the parameters responsible of this life decrease. The present paper focused on both definition and characterization of internal damage occurring during pure cyclic, dwell fatigue and creep test conducted on a β-forged Ti-6242 alloy. The internal damage consists in small cavities which nucleate along sharing bands at the α/β interfaces. The mechanism, much intense under both dwell-fatigue and creep loading than under pure cyclic loading, is progressive and localized. The EBSD analyses performed on the sheared colonies shows that the shear occurs on pyramidal slip plan, what was confirmed by TEM analyses.