PSI - Issue 66

C. Bellini et al. / Procedia Structural Integrity 66 (2024) 518–524 Author name / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 3. Fatigue fracture micromechanisms corresponding the stage 1.

In the second stage, the one characterized by the increase in the slope of the da/dN- ∆ K curve, the fracture micromechanisms become less and less ductile and the propagation, although markedly transgranular, in some areas crosses the grain boundaries, giving rise to “stepped” morphologies (Fig. 4). At this stage, the presence of nanoparticles no longer constitutes an efficient obstacle to crack propagation, which is governed by traditional intergranular/transgranular micromechanisms with a strong increase in the slope of the da/dN- ∆ K curve.

Fig. 4. Fatigue fracture micromechanisms corresponding to stage 2.

This is even more evident in the last stage, where it is possible to observe the fatigue striations present especially at the transgranular level, as reported in Fig. 5. Under these conditions, there is no evidence of the influence of nanoparticles on the fatigue behavior, probably because the fatigue crack advancement rate is too high compared to