Nucleation of cracks from shear-induced cavities in an α/β titanium alloy in fatigue, room-temperature creep and dwell-fatigue

• Published in: Acta materialia 2008-09, Vol.56 (16), p.4450-4457
• Main Authors: Lefranc, P., Doquet, V., Gerland, M., Sarrazin-Baudoux, C.
• Format: Article
• Language: English
• Subjects: Applied sciences; Cavity nucleation; Creep; Dislocation dynamics; Exact sciences and technology; Fatigue; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Titanium alloy
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2008.04.060

In titanium alloys, dwell periods during room-temperature stress-controlled fatigue tests are responsible for substantial reductions in lifetime compared to pure fatigue loading. The mechanisms of such a creep–fatigue interaction have been investigated for alloy Ti-6242. Scanning and transmission electron microscopy observations revealed crack initiation by coalescence of shear-induced cavities nucleated at α/β interfaces in large colonies of α laths nearly parallel to the loading axis. The density and average size of cavities were larger in dwell-fatigue and creep than in fatigue. A qualitative micromechanical model of cavity nucleation based on discrete dislocation dynamics was developed. The number of cycles for cavity nucleation was computed as a function of the applied stress range. A finite threshold, dependent on the size of α laths colonies with similar orientation, was found. The simulations predict earlier cavity nucleation in creep or dwell-fatigue than in pure fatigue, which is consistent with the performed experiments.