PSI - Issue 68

Vahid Javaheri et al. / Procedia Structural Integrity 68 (2025) 1098–1104 V. Javaheri et. al, Structural Integrity Procedia 00 (2025) 000–000

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In contrast, the fractography of the hydrogen-charged sample (Fig. 3b) reveals a different fracture mode. The presence of hydrogen significantly alters the fracture surface morphology. The most prominent changes include the noticeable reduction of shear lips, alongside the development of embrittled zones that propagate from the surface into the sample's interior. Numerous secondary microcracks, oriented perpendicular to the main crack, are visible, further indicating the presence of hydrogen-induced embrittlement. These microcracks suggest that hydrogen weakened the sub-boundaries and interfaces , resulting in a brittle fracture behavior. Same phenomenon was reported previously by (Liu et al., 2023). A detailed examination of the cross-sectional view of the hydrogen-charged sample is presented in the magnified image in Figure 4, offering additional insights into the localized fracture mechanisms. During plastic deformation, as indicated in Figures 4a and 4b, a considerable amount of the unstable RA(γ) transforms into fresh martensite (α′) near the fracture surface. This transformation alters the local microstructure, turning the original γ/α interfaces and γ grain boundaries into body-centered cubic (BCC) α′ boundaries. More specifically, the fraction of RA(γ) decreases significantly from around 40% in the unstrained region (Fig. 4c) to approximately 10% in the areas subjected to the highest strain near the fracture (Fig. 4a, b).

Fig. 4. The cross-section banc contrast (BC) and phase map of the pre-charged sample at different region a) and b) near the fracture surface and c) far from the fractured and strained region