PSI - Issue 37

G. Macoretta et al. / Procedia Structural Integrity 37 (2022) 632–643 G. Macoretta, B. D. Monelli / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 8. Wöhler curves for the tested sets of process parameters.

3.5. Fractographic examinations The fractographic examination carried out by stereomicroscope and SEM showed that for all the tested specimens the fatigue crack onset occurred on the specimen surface, in correspondence with local defects caused by the waviness of the as-built surface, Fig. 9 and Fig. 10. In proximity to the fracture onset, no significant pores were observed, but the surrounding area presents several pores and in the case of the A1 and A2 process parameters, Fig. 9 (b) and (c). In the case of the A1 set, for several specimens the fracture arose from macroscopic defects present on the surface, consisting in a local area of lack of fusion on the external surface probably due to instabilities in the meltpool and to an uneven powder spread caused by the wear of the recoater wiper produced by raised borders.

Fig. 9. SEM images of the fracture onset region: (a) baseline , (b) A1 , (c) A2 process parameters set.