PSI - Issue 68

Giuseppe Macoretta et al. / Procedia Structural Integrity 68 (2025) 974–980 G. Macoretta et al. / Structural Integrity Procedia 00 (2025) 000–000

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3. Results and discussion 3.1. Microstructural analysis and local notch geometry investigation

The microstructural analysis revealed that the adopted process parameters produced a full-dense material, with only some sporadic pores due to gas-entrapped bubbles, Fig. 3 a). This result is in line with the pieces of evidence of the previous works that adopted the same or equivalent process parameters, [8,9,15,16]. The investigations carried out on samples in longitudinal direction showed that after the heat treatment, the traces of the L-PBF process are still evident, but no meltpool boundary precipitates can be detected. A columnar structure with grains elongated in the build direction, the longitudinal direction for the specimen, can be observed Fig. 3 b). The material microstructure resulted to be homogeneous within the specimen cross-section and along the specimen build direction. The detail of the notch geometry produced by the L-PBF process is shown in Fig. 4. The profile turned out to be almost in line with the nominal dimension in the case of the blunt notches, while it significantly differs for the shaper ones. This effect is due to the unavoidable stair-stepping effect introduced by the L-PBF process, which becomes more evident when the number of layers that form the specimen notch region is lower. As shown in Fig. 4 a), the effective notch radius (0.13 mm) resulted to be almost halved compared to the nominal value (0.21 mm) for the sharpest notches, when 5 layers are present in the notch radius region. Conversely, the difference between the nominal and the effective notch radius was lower than 5% for k t 1.5 and k t 2 specimens, Fig. 4 b).

Fig. 3. Specimen microstructure in transverse (a) and longitudinal (b) sections. Etchant Kalling’s II.

Fig. 4. Notch radius (R) investigation for specimens featuring k t 3.5 (a) and k t 2.0 (b) notches. Etchant Kalling’s II.