PSI - Issue 54

Daniel F.O. Braga et al. / Procedia Structural Integrity 54 (2024) 631–637 Daniel F.O. Braga et al. / Structural Integrity Procedia 00 (2023) 000–000

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Fig. 1. Schematic of (a) SLM process; (b) LMD process.

cooling control during LMD process was shown to be challenging regarding melt pool dimensions and process stability. The authors list as advantages of this process chain, the part complexity flexibility, with more complex sections made through SLM and least complex with LMD, the ability to employ dissimilar material manufacturing through LMD and the increase in build rate, which improves production scale. Petrat et al. (2016) demonstrated the use of this process in repair of SLM components through LMD, and Petrat et al. (2018) demonstrated the integration of electronics onto components manufactured with this hybrid SLM, LMD approach. Uhlmann et al. (2019) studied the effect of heat treatment in Inconel 718 manufactured through SLM and LMD, as a way of mitigating the variations in mechanical properties within the various regions due to the different thermal signatures of the manufacturing processes. It was found through optical microscopy analysis and hardness measurement the uniformity of the structures achieved through this combined process chain was enhanced, but some microstructure dissimilarity induced by each additive manufacturing process remains. Liu et al. (2016) studied both microstructure and mechanical properties of LMD-SLM hybrid manu facturing in Ti6Al4V alloy. Three processing methods were studied, LMD deposition in same direction as SLM, LMD deposition perpendicularly to SLM and LMD deposition on rolled plate. Grain growth along the reverse direction of the temperature gradient (powder accumulation) was found, resulting in coarser grains in the heat affected zone (HAZ) due to the laser reheating process. Even though SLM, resulted in hard α ’ martensite phase, LMD reheating, this phase was decomposed and a hardness decrease was achieved, but the lowest hardness was still in the LMD region, resulting in ductile failure in this region, and elongation > 10%, in hybrid SLM-LMD specimens. The failure mode in the hybrid SLM-LMD, with both LMD deposited in the same direction as SLM or perpendicular, was similar to the one observed in LMD depositions on top of rolled plate. 2. Fatigue in Metal AM Fatigue is reported to be the main failure mechanism for mechanical failures of aircraft components, Findlay and Harrison (2002), and with the further adoption of AM technologies in aeronautics and aerospace applications, it is expected that this trend will be preserved, Gorelik (2017). As such, fatigue strength and fatigue life of AM components is a critical consideration for structural integrity of metal AM parts and its adoption in safety critical applications. Frazier (2014) reviewed metal additive manufacturing processes and their structural integrity issues with emphasis on aeronautical and aerospace applications. Regarding fatigue, it was shown that surface roughness and micro-porosity resultant from the additive manufacturing process dominated fatigue properties. Given the high cooling rates achieved in these processes, mechanical properties show anisotropy, and generally the Z direction is the weakest. The anisotropy, as well as the surface roughness and micro-porosity can