PSI - Issue 54

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Daniel F.O. Braga et al. / Procedia Structural Integrity 54 (2024) 568–574 Daniel F.O. Braga et al. / Structural Integrity Procedia 00 (2023) 000–000

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a)

b)

c)

Fig. 1. Scheme of hybrid manufacturing process a), TS700 LMD deposition on top of SLM b) and resulting block before specimen machining c)

3. Results and Discussion In Fig. 2 it is shown the resulting cross-section with increasing magnification after sanding, polishing and etching of the interface of DIN 1.2709 tool steel, produced through SLM, at the bottom in the images and TS700 tool steel, produced through LMD at the top. Due to etching it is clearly visible the mesostructure difference between both materials and due to manufacturing process. At the top, large beads are visible, with width of ≈ 1 mm, and height of ≈ 0.28 mm, with close to 50 % overlap between beads. Build direction is aligned with the vertical axis of the image. At the bottom the SLM deposition, it is possible to observe the layer transitions perpendicular to the the material transition. The layer height observed in the SLM material is ≈ 0.1 mm, and bead width is only partially visible at higher magnifications and is ≈ 50 µ m. A layer of ≈ 50 µ m in the bottom material appears in a slightly darker tone than the remaining material, which may indicate some remelting of the material at the top layer, and perhaps some second phase formation. However further metallographic analysis would be required to determine the chemical composition in each of these regions, to determine microstrutural changes at this transition region. No clear intermetallic region is observed, even though further analysis would be required to attest to this. A darker transition region of ≈ 2.5 µ m is observed in between the SLM material and the LMD material, as well as in between the 0.5 mm width of SLM material and the remaining. If intermetallics were formed it would be expected that these would be located in these regions. Given that both materials are tool steel alloys, the dissimilarity between both is small, decreasing the probability of intermetallic formation. Overall the Stress vs. Strain behaviour was consistent between process parameter sets tested. An example of an engineering stress vs. strain curve is shown in Fig. 3, for run order #1, which is a center point of the CCD, 1300 W laser power, 900 mm/min scan velocity and 10 g/min powder feed. Overall low strain hardening is observed as the difference between ultimate and yield strength is small. The UTS and elongation of these