PSI - Issue 54

Daniel F.O. Braga et al. / Procedia Structural Integrity 54 (2024) 626–630 Daniel F.O. Braga et al. / Structural Integrity Procedia 00 (2023) 000–000

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can be achieved derived from the geometric freedom provided by these methods. These factor have led to significant research e ff ort onto the additive manufacture of these alloys as reported by Zafar et al. (2023).

Nomenclature

CCD Central Composite Design DoE Design of Experiments DIC Digital Image Correlation LMD Laser Melting Deposition SLM Selective Laser Melting UTS Ultimate Tensile Strength YS Yield Strength

Inconel 625 is a solid solution-strengthened alloy, which can also undergo strengthning by carbide and / or in termetallic compound precipitation, Sundararaman et al. (1988). It has been demonstrated to have significant high temperature tensile strength and creep resistance, Son et al. (2020), among other mechanical properties, making them suited to high temperature applications. As reported by Zafar et al. (2023), when additive manufactured though Laser Metal Deposition (LMD), Inconel 625, generally results in lower ductility, with maximum elongation lying between ≈ 60 and 65 % of conventionally fabricated. LMD Inconel 625 presents mechanical properties dependent on the direction relative to the build platform, with ultimate tensile strength (UTS) and yield strength (YS), within 820-880 MPa and 460-600 MPa respectively in the horizontal direction (XY) and 730-840 MPa and 370-510 MPa in the vertical direction (Z). Inversely, elongation is higher in the vertical direction with values reported within 40-56 % in the horizontal direction and 29-45 % in the vertical direction. Eventhough Selective Laser Melting (SLM) results in finer micro and meso-structure, with improved strength and ductility compared to LMD, these di ff erences may be mitigated through proper post-treatment of AM build, as demonstrated by Nguejio et al. (2019). Kreitcberg et al. (2017) showed that hot isostatic pressing can be used in metal AM of Inconel 625 to produce isotropic equiaxed microstructure with improvements in ductility of the produced components. Marchese et al. (2017) studied both SLM and LMD process of Inconel 625, achieving higher deposition rates with LMD but lower dimensional accuracy. The reported hardness of Inconel 625 was 220 HBW, comparable with commercially available as-rolled alloy while SLM resulted in a higher average hardness of 290HBW. Design of Experiments (DoE) has been an approach undertaken to study metal AM, including Nickel based su peralloys. Moradi et al. (2021) used DoE to study selective laser melting (SLM) of Inconel 718, namelly the e ff ect of scanning speed, powder flow rate, and scanning pattern on height of AM wall, average width of AM wall, and stability of AM wall and microhardness of AM wall. For the alloy and process studied the authors found an optimum parameter set of 2.5 mm / sec scanning speed, 28.52 g / min and unidirectional scanning pattern, based on the outputs selected. Yang et al. (2020) used Taguchi method and Grey Relational Analysis to study LMD Inconel 625, namely the e ff ect major process parameters on surface roughness and width error. The most influential process parameters for the two outputs selected was overlapping rate and the optimum levels found for the process parameters were, 1800 W laser power, 8 mm / s scanning speed, 10 g / min powder feed rate and 30% overlapping rate. In this study, DoE was used to study LMD process of Inconel 625 and optimize the process towards component strength. By employing DoE methodology, it is intended to achieve a prediction model, enabling the prediction of me chanical strength derived from process parameters employed and this way maximize strength through proper process parameter definition.

2. Materials and methods

For DoE a Central Composite Design (CCD) with a distance of each axial point ( α ) of 2 was used, varying laser power, scan speed and powder flow, with the remaining process parameters kept constant. The process parameters are listed in Table 1.