PSI - Issue 53

Omid Emadinia et al. / Procedia Structural Integrity 53 (2024) 278–284 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Figure 2 (a) Macrostructure along the build height of the specimen; (b) DM images from the bottom and top most regions; (c) SEM-BSI of similar zones, illustrated as the “bottom” and “topmost” regions

Figure 3 shows the grain structure of the similar zones as analyzed in Figure 2, i.e., the bottom and the top most regions of the printed structure. A much finer grain size was evident in the bottom region as compared to the topmost region. In the earliest steps of printing, the cooling rate should have been high (GxR ↑ ) since the substrate was at room temperature and the heat was easily dissipated by conduction through AISI 4140 substrate. This behavior has resulted in the evolution of finer grained structure in the bottom zone as compared to the top most region. The grain growth along the building direction observed in the Inconel 625 alloy printed continuously by L-DED. This evolution is highlighted at the top most region since the accumulation of heat lead to a decrease in cooling rate (GxR ↓ ) (Kou 2003) (Ali, Tomesani et al. 2022, Ferreira, Reis et al. 2022, Gao, Shi et al. 2022) contributing the grain growth. Regarding the phase evolution along the printed material, the matrix of the Inconel 625 is constituted by gamma phase and as the characteristic of a printed and non-heat-treated alloy the microstructure includes secondary phases such as Laves phase and complex oxides (Ferreira, Reis et al. 2022, Zafar, Emadinia et al. 2023). As Figure 4 shows, the distribution of Nb and Mo in the matrix confirms the evolution of the Laves phases (as depicted by white spots in the micrographs) and the black spots in the microstructure are confirmed as complex oxides that is in agreement with previous studies. The concentration of the laves phases did not seem to be significantly different in the bottom and top most region of the printed thin-walled structure. Future works shall include the X-ray diffraction analysis of these two regions for phase identification and quantification.