PSI - Issue 75

Kalle Lipiäinen et al. / Procedia Structural Integrity 75 (2025) 19–28 Lipiainen et al./ Structural Integrity Procedia (2025)

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thermal histories since they have relatively more refined microstructures, and tracks of interlayer boundaries are still visible in the EOS S sample [Fig. 7(c)]. This point might cause a different mechanical performance in the additively manufactured materials, considering the positive influence of α’ on the fatigue performance of Ti64 (Liu & Shin, 2019). Regarding the defect distribution of the additively manufactured samples, all the specimens showed satisfactory build qualities with relative densities estimated to be higher than 99.9%. The presence of internal defects, i.e., porosities and lack-of-fusions, in the additively manufactured components, was sporadic and rare, as shown in Fig. 7. According to the figure, all the specimens had both defect types of porosity (marked by gray arrows) and lack-of fusion (marked by dark arrows) in internal and subsurface areas. The average diameter of the porosities ( ≤ ≈ 30 μ m) was relatively smaller than the largest dimension of lack-of-fusions ( ≤ ≈ 50 μ m). Also, the presence of lack-of fusions was comparably less noticeable than porosities in all the samples. High quality is in-line with the fatigue test results presented in Fig. 2.

Fig.7 Microstructural features overall views of defects and their distribution in the specimens: (a) SLM B, (b) EOS G, (c) EOS S and SLM W series. However, lack-of-fusions had sharp corners aligned along the scanning plane, which can act as internal stress risers inside the additively manufactured component, as marked with red arrows in Fig. 8, especially when the applied external load is parallel to the building direction. It should be noted that such lack-of-fusions are less frequent in the EOS S specimen compared to the others. Finally, the presence of surface inhomogeneities, such as stuck powder particles and sudden intrusions (with occasional sharp roots), was prominent, as marked by cyan arrows in Fig. 8, due to the layer-by-layer deposition of powder layers being the inherent mechanism of L-PBF as the AM procedure used in this study. Subsurface imperfections are marked with red arrows.

Fig.8 Imperfections and surface features in the specimens: (a) SLM B, (b) EOS G, (c) EOS S, and (d) SLM W.