PSI - Issue 65

Boris Voloskov et al. / Procedia Structural Integrity 65 (2024) 302–309 Voloskov et al./ Structural Integrity Procedia 00 (2024) 000–000

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pool, creating voids as gas escapes. These voids can lead to significant porosity within the final part (Kan et al. 2022). In general, the higher volumetric energy density is needed, as the surface of the part experiences significant heat loss to the surrounding environment. Therefore, it requires higher energy input to maintain sufficient temperature for melting and fusing the powder particles effectively (Ranjan et al. 2020). However, optimizing these parameters is essential to ensure the quality of the final part.

Fig. 5. (a) volume fraction of pores; (b) normalized cumulative volume fraction of pores; (c) shape analysis of pores; (d) shape analysis of pores.

The shape analysis of the pores is shown in Fig. 5c and Fig. 5d excluding pores at contour region of 200  m. Equivalent diameter is a diameter of sphere with the same volume. 3D aspect ratio is a ratio between max and min Feret’s diameter. Pore sphericity is a measure of how closely the shape of a pore resembles that of a perfect sphere. It is defined as the ratio of the surface area of a sphere with the same volume as the pore to the actual surface area of the pore (when 1 for perfect sphere). NP strategy produces less pores than chessboard strategy, however, with shape that is more irregular. Most of the pores in chessboard strategy are spherical. The chessboard pattern promotes better heat distribution across the melt pool. By alternating scan directions and leaving gaps, it helps manage heat more effectively, reducing localized overheating or underheating, which are common causes of incomplete melting and fusion (Ali, Ghadbeigi, and Mumtaz 2018). This particular feature likely contributes to a decrease in lack of fusion defects. The tensile characteristic obtained revealed its dependence on hatch distance and scanning strategy. As hatch spacing increases, the overlap between adjacent tracks decreases. This can lead to lack of fusion defects and increased porosity in the material, which can negatively affect tensile strength and ductility (Mao et al. 2024; Harkin et al. 2023). As the hatch spacing decreases, the absorbed energy increases, which helps remelt the previous track. This remelted liquid fills in the gaps, creating a continuous bond between the tracks (Pei et al. 2017). A smaller hatch spacing contributes to finer grain structures due to more uniform thermal conditions and reduced cooling rates. Finer grains typically enhance ductility by providing more slip systems for dislocation movement, allowing the material to deform more easily under stress (Dong et al. 2018; Popov Jr. et al. 2018).