PSI - Issue 53

Luca Marchini et al. / Procedia Structural Integrity 53 (2024) 203–211 Author name / Structural Integrity Procedia 00 (2019) 000–000

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3. Results and discussion Figure 2b shows the horizontal cross-section (SD) microstructure of the AM sample. Despite the aging heat treatment, the superimposed elongated scan paths, characteristic of as-fabricated AM components, are still visible. Additionally, the vertical cross-section (BD) of Figure 2a reveals semi-elliptical molten pools, with dimensions that are consistent with the laser scan parameters and construction strategy employed. Importantly, the porosity detection with optical microscope images analysis resulted in a 99.82 ± 0.08 % dense material. Unetched regions are observable at the boundaries and inside the melt pools in both vertical (Fig. 2a) and horizontal cross-section section (not depicted in Fig. 2b). Figure 2c shows the microstructure of F samples after solution treatment and aging. Nital 2% samples reveal blocks or packets of lath-type martensite with extremely fine unetched boundaries. On the other hand, the structure of the H11 tool steel consists of a fine dispersion of small spheroidal carbide particles in a matrix of ferrite (Fig. 2d).

Fig. 2 – All the images were taken after etching the samples with Nital 2%; (a) AMed sample, the presence of the melt pools indicates the section perpendicular to the building direction (BD); (b) AMed sample, the presence of the scant tracks indicates the section perpendicular to the scanning direction (SD); (c) Forged sample; (d) H11 sample. The plot in Figure 3a shows the thickness loss of different samples versus the immersion time. It is evident that the AM maraging steel exhibits a superior corrosion resistance compared to the forged one. In fact, in case of forged material, it was not possible to evaluate the thickness loss after 4 hours of immersion due to the strong dissolution of these samples in the Al bath. On the other hand, as expected, the more conventional H11 steel exhibits the best corrosion resistance.