PSI - Issue 7

A. Brueckner-Foit et al. / Procedia Structural Integrity 7 (2017) 36–43 A. Brückner-Foit / Structural Integrity Procedia 00 (2017) 000–000

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a) b) Fig. 5 a) Fracture surface of specimen failed at 87.5 MPa, 218,278 load cycles; large shrinkage pore with rough fracture surface and interaction with gas pores; b) detail showing dendritic structure of shrinkage pore and interaction with gas pores.

However, the most common case was the one in which an interaction between defects occurred, leading to premature failure. This phenomenon is very likely to happen since gas pores are prone to agglomerate around shrinkage pores in the inter-dendritic spaces (see Fig. 2 and Fig. 6) and promote multiple crack initiation.

Fig. 6 Fracture surface of specimen failed at 140 MPa, 45,065 load cycles; large shrinkage pore with rough fracture surface and secondary cracks (blue arrows).

3.2 The role of Fe-rich inclusions The SEM observations showed no direct influence of the ß-Al 5 FeSi inclusions on the fatigue damage process. Moreover, a higher concentration of these particles was observed in the inner part of the specimen, which can explain their limited effect on the fatigue life. The 3D reconstructions show the arrangement of these Fe-rich particles in agglomerations of complex clusters of inclusions distributed along the specimens (see Fig. 7a and 7b). Therefore, the inclusions that in the 2D metallographic pictures are seen as individual needle-like particles may actually belong to a larger single inclusion comprised of plate like particles.