Defect features critical to the fatigue of additively manufactured Ti-6Al-4V

This study aimed to identify the morphological features of process-induced volumetric defects most influential on the fatigue behavior of laser powder bed fused Ti-6Al-4V. Fatigue test specimens were machined from round bars fabricated using eight distinct process parameter sets and three build orientations to ensure a wide range of defect morphologies and populations. Uniaxial, constant amplitude, fully-reversed fatigue tests were conducted on these specimens until failure. Fractography was performed to identify the defect responsible for the fatigue crack initiation and extract its morphological features. The influence of these features on fatigue behavior was examined by analyzing experimental data and finite element analysis results. While size was the most critical defect feature influencing fatigue behavior, it could not fully explain the variation in fatigue life by itself. For defects of similar size located at the same location, circular defects appeared to be more detrimental than irregularly shaped ones. A new defect size parameter, the square root area of the maximum inscribed circle, was introduced to partially account for both the size and shape of the volumetric defects, which exhibited a strong correlation with life compared to existing parameters.