FATIGUE CRACKS INITIATION AND PROPAGATION BEHAVIOR IN WELDED JOINTS OF TITANIUM ALLOY

摘要

In this article, in-situ observation upon the dynamic extension of low cyclic fatigue cracks in weld fuse zone(FZ) and heat affected zone(HAZ) for TA15 titanium alloy were carried out. The results show that there are both two stages(stage I and stage II) during the process of fatigue crack propagation in FZ and HAZ. Slips at the tip of the cracks in FZ are very clear in the whole crack growth process and slip lines are much longer than those in HAZ which can only be found in fast expanded area. The fatigue cracks in HAZ are more deviated and bifurcate than those in FZ during the process of fatigue cracks propagation. And more secondary cracks are also found near the main crack at the surface of HAZ. Furthermore, the crack growth rates in FZ are larger than those in HAZ. It is concluded that the different fatigue crack growth behaviors between HZ and HAZ are related to different microstructures.