Abstract: Room-temperature (RT) creep may happen below yield stress in titanium alloys, while the creep asymmetry remains pending under various stress states. The creep behavior and plastic damage were investigated during the early-stage RT-creep up to 60 h in a titanium alloy. The investigated TC4 ELI Ti-alloy is a high-purity (“Extra-Low-Interstitial”) version of Ti-6Al-4V with a near-α type microstructure after thermomechanical treatment. Three kinds of creep testing were conducted, including axial tension, compression, and torsion, respectively. The microstructure and especially, dislocation behaviors were analyzed in detail by using electron backscattered diffraction, transmission electron microscopy, and X-ray diffraction after an interrupted and terminated creep testing. The creep strain differs, which is 5 %, 1 %, and 0.5 % under tension, compression, and torsion, respectively. It undoubtedly indicates the presence of creep asymmetry. To clarify the creep mechanism, the slip system was then analyzed. It is shown that the prismatic slip is dominant during tensile creep, while the pyramidal slip appears most during compressive creep. The limited slip transmission and immobile dislocations result in lower creep strain. The reason behind the creep asymmetry is attributed to the stress state, producing the activation of various slip systems, along with the evolution of true stress. Finally, the mechanistic origins are also discussed as to the distinctive creep rate under various stress states.

Key words: TC4 ELI alloy, Creep, Stress state, Microstructure, Dislocation slip