Effect of notch on the high and low cycles fatigue of TC21 alloy

The effect of notch on the high cycle and low cycle fatigue strength of TC21 alloy at different temperatures has been investigated in this paper. The fatigue specimens contain two kinds of the stress concentration factors, K_t=1 and K_t=3. The fatigue tests were performed in load-controlled mode and the cyclic stress ratio is 0.1. The high cycle fatigue (HCF) tests were performed at 315°C, and the low cycle fatigue (LCF) tests were performed at room temperature and 400°C. The results indicated that the notch decreases the fatigue strength when the cyclic stress is lower and the plastic deformation does not take place at the root of the notch. When the cyclic stress is higher so that the plastic deformation happens at the root of the notch, the effect of notch on the fatigue strength decreases. When the cyclic stress is high enough to make the unnotched specimens unstable, the fatigue strength of notched specimens is higher than the unnotched specimens. SEM fractography indicates that the fatigue cracks of notched fatigue specimens nucleate at the surface by multiple sources, even in the HCF conditions.