High cycle fatigue behavior of CMT wire arc additively manufactured Ti6Al4V: Fatigue anisotropy and porosity sensitivity

As wire arc additive manufacturing (WAAM) of Ti6Al4V gains increasing application across various fields, its fatigue performance has attracted growing attention. This study investigates the microstructure and high cycle fatigue (HCF) behavior of cold metal transfer (CMT)-WAAM Ti6Al4V at different sampling locations. The results reveal the presence of a heterogeneous microstructure in WAAM Ti6Al4V. Although this heterogeneity induces fatigue anisotropy, pore defects remain the dominant factor governing fatigue performance. Quantitative analysis of pore characteristics indicates that pore sizes primarily affecting fatigue life range from 53 to 300 μm, while the depths of fatigue pores are mainly concentrated in two regions: 0–20 μm and 20–150 μm from the surface. Meanwhile, the calculated stress intensity factors (SIFs) for crack initiation from surface and internal pores range from 1.50 to 3.25 MPa∙ and 2.02 to 3.25 MPa∙ , respectively, confirming the sensitivity of fatigue performance in CMT-WAAM Ti6Al4V to pore defects. Furthermore, fatigue limits were predicted using the Gumbel distribution and Kitagawa-Takahashi (KT) diagram, identifying the critical pore sizes for fatigue crack initiation at the surface and in the interior as 52.32 μm and 88.42 μm, respectively. This study expands the fatigue database of WAAM titanium alloys and highlights the importance of defect evaluation in additive manufacturing. The findings contribute to the optimization of WAAM process parameters and the improvement of structural reliability of Ti6Al4V components in aerospace and other applications.