Fatigue crack growth behavior in additive manufactured Ti6Al4V alloy with intentionally embedded spherical defect

The present study aims at elucidating the impact of unavoidable defects in selective laser melting (SLM) additive manufactured alloys on fatigue performances. The novel idea is to reveal the relationship between the printing defect and fatigue crack growth, by intentionally embedding a 500 μm spherical defect in an SLM-Ti6Al4V alloy exerted to low-cycle fatigue (LCF). The results show that the cyclic softening of the specimen was not affected by the embedded defect and surprisingly its fatigue life was nearly the same as the virgin specimens free of embedded defects at low strain amplitudes. The performance is attributed to the single crack initiation site and only small change in the stress intensity factor range (ΔK). In contrast, when subjected to higher strain amplitudes during LCF, the embedded defect dominates the crack initiation and crack propagation occurs readily. It is shown that the experiments support a model description based on the competitive failure mechanisms between the surface defects and internal defects.