PSI - Issue 66

R. Fernades et al. / Procedia Structural Integrity 66 (2024) 49–54 Author name / Structural Integrity Procedia 00 (2025) 000 – 000

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Scanning electronic microscopy analysis of the failure surfaces were performed in order to observe failure modes and failure paths. Fig. 3) shows an image for HIP specimen in Regime II. The observation of this figure indicate that the propagation is predominantly intergranular, but zones of a crack path in an intralayer way are observed, where crack to pass through the areas with prevalent defects, like porosities and lack of fusion.

Fig. 3. Fracture surface examination by SEM in Regime II ( Δ K= 6 MPa √ ) for HIP series. Lateral macrographs of the three-specimen series were carried out in order to observe crack path and complement SEM observations. Fig. 4 shows three of these macrographs for AS, SR and HIP specimens, respectively. The analysis of the figures confirms what before stated, crack propagation is predominantly interlayer, with some intralayer failure nearly boundaries. Propagation modes are quite similar for the three material conditions.

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Fig. 4. Lateral macrographs: a) AB specimens; b) SR specimens; c) HIP specimens.

A batch of tests were carried out including the application of single overloads with ORL=2. Failure surfaces of the three material conditions were observed in a 3D optical microscopy. Figs 5a) and 5b) show two of that observations for AB and SR specimens, respectively. These images show the presence of numerous micropores and intense overload marks. Failure surfaces are similar for the three material conditions. Fig. 6 compares the failure surface of two specimens (AB and SR specimens) where were applied three single overloads of ORL=2. For AB specimen the marks of the 3 overloads are visible and the final failure occurs immediately after the third overload. Contrary, for the SR specimen only the mark at the 3th overload is visible and the crack propagation proceed after the third overload until final failure occurs. This means that the heat treatments promoted an increased ductility and toughness.