Designing the microstructure of additively manufactured IN 718 components by optimizing the process and heat treatment parameters to improve mechanical properties

Date

2023-9-11

Author

Kaleli Alay, Tuğçe

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The microstructure of additively manufactured IN718 (IN 718) often shows microsegregation of some alloying elements at the interdendritic area. This results in a formation of irregularly shaped Laves phase, which serves as the main site for the nucleation of microvoids under tensile loads. Post-processing heat treatments and the laser scanning strategy used for the manufacturing process might be modified to control the size and morphology of the Laves phase and dislocation density and to enhance the strength and ductility of the superalloys. To achieve this, a novel Time Homogenization (TH) scanning strategy was developed for IN718 alloys. The laser powder bed fusion method (L-PBF) was applied to produce specimens with a 52 J/mm 3 energy input. Moreover, three heat treatment procedures, such as Direct Aging (DA), Solutionizing and Direct Aging (STA), and Homogenization, Solutionizing and Direct Aging (HSTA) were applied. The microstructural features, microhardness, and tensile properties of as-built and heat-treated specimens were studied and verified with physical metallurgy phenomena such as precipitation strengthening and dislocation movement. The as-built TH specimens showed fine and granular Laves phases, while the as-built SP specimens had coarse and chain- like Laves phases. Furthermore, TH specimens demonstrated an enhanced combination of strength and ductility after heat treatment at room and elevated temperature.

Subject Keywords

Ni-based superalloys, Additive manufacturing, Laser powder bed fusion, Scan strategy, Elevated temperature, Mechanical properties

URI

https://hdl.handle.net/11511/105531

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Graduate School of Natural and Applied Sciences, Thesis