Pore-induced fatigue failure: Critical pore criterion for Ti-6Al-4V alloy manufactured by laser-directed energy deposition

Pores are the major factor inducing fatigue failure in laser-directed energy deposition (L-DED) Ti-6Al-4V alloy, posing obstacle to the application of the alloy in primary load-carrying components. Hence, it is essential to formulate criteria to identify critical pores that induce failure, an important step in evaluating the fatigue performance and predicting the fatigue life of L-DED Ti-6Al-4V alloy. In this paper, computed tomography was performed on tangentially blending fillets specimens to examine the distribution characteristics of pore geometric parameters, and location in the gauge section of the specimens. Then, fatigue experiments and fracture analysis were conducted. The results show that the location relative to the surface, size, and shape of the pores are the primary factors affecting fatigue failure. A stress state sensitive parameter was formulated by using location factors, projected area along the load direction, circularity of pores, and peak stress to establish a criterion for recognizing critical pores, the number of which can be reduced to two. The critical pore criterion based on stress state sensitive parameter was compared with those obtained via the other methods, proving its good applicability and effectiveness on identifying critical pores.