PSI - Issue 47

P. Ferro et al. / Procedia Structural Integrity 47 (2023) 535–544 P. Ferro et al. / Structural Integrity Procedia 00 (2023) 000–000

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3. Results and Discussion 3.1. Filaments’ characterization Fig. 3 shows scanning electron microscope images of the cross-section of the two filaments used in FDMS process.

Fig. 3. SEM images (at the same magnification) of the cross-section of a) HCS and b) IN718 Filament

The HCS/polymer composite filament consists of a dispersion of irregular shaped particles which size ranges from 80 to 200  m; while the IN718 filaments is composed by regular spherical shaped particles which dimension varies from 15 to 40  m. Despite the binder plays a principal role in the printing process so that the requirement on the morphology of the dispersed metal particles, including the sphericity, fluidity, and size distribution, is not as rigorous as that for selective laser melting (SLM) or other metal 3D printing methods, the evident difference in particle size between the two alloys could play a fundamental role in the subsequent heat treatment. Focusing on the microstructure of the HSC powder, it is revealed, after chemical etching, that the microstructure is, as expected, composed by a pearlite matrix which grains are decorated by secondary cementite (Fig. 4a). This was confirmed also by Vickers microhardness measurements on the two microstructural constituents carried out with a load of 25 g (pearlite: 320  36 HV; cementite: 1318  102 HV) (Fig. 4b)

Fig. 4. Images of HCS powder: SEM micrograph and b) Vickers hardness indentations

About IN718 powder, a solidification microstructure is visible with interdendritic segregations of heavy elements, such as Nb, as identified by EDS analysis of clear areas in Fig. 5a (Table 3). The Vickers microhardness (load 25 g) was 288  17 HV.