Effect of Post-Weld Heat Treatment on the Fatigue Properties of Dissimilar Titanium Alloy Joints

摘要

The purpose of this study was to characterize the microstructural change and fatigue resistance of electron beam welded (EBWed) dissimilar joints between Ti-6Al-4V and BT9 (Ti-6.5Al-3.5Mo-1.5Zr) alloys after two types of post-weld heat treatment (PWHT), namely only aging and solution treatment followed by aging (STA). It was observed that no significant microstructural change occurred in the FZ after only aging and the high hardness in the fusion zone (FZ) remained, while coarse acicular α occurred in the FZ in the STA condition, leading to a reduced hardness. Both types of post-welded joints were cyclically stable at lower strain amplitudes of 0.2-0.6％, and exhibited cyclic softening at higher strain amplitudes of 0.8％-1.2％. As the total strain amplitude increased, cyclic stress amplitude increased, while the fatigue life decreased. Fatigue crack initiation occurred from the specimen surface or near-surface defects and propagation was characterized mainly by the formation of characteristic fatigue striations.