Additive manufacturing of Inconel 718: characterizing parts and powders

This study demonstrates that fast non-destructive testing using X-ray fluorescence(XRF) and X-ray diffraction (XRD) has the sensitivity necessary to detect minor variations of consequence in parts and recovered powders used in near-net-shape production with Inconel 718.

Nickel-Iron super-alloys, such as Inconel, are well suited for use in hostile high-temperature environments that require good creep, corrosion, and thermal shock resistance. Such super-alloys are favored for hot sections in aircraft engines and other demanding applications. Near-net-shape processes, such as additive layer manufacturing (ALM) or hot/cold isostatic press (HIP/ CIP), are appealing because they can produce new and complex shapes that minimize weight while still providing mechanical integrity under hotter combustion conditions for improved fuel efficiency. Microstructural hardening mechanisms, such as solid solution strengthening or precipitation of intermetallic compounds, can also be engineered into the near-net-shape manufacturing process.

In order to minimize waste in additive manufacturing and powder metallurgy processes, it is good practice to reuse the excess powder left over after each build. The recovered powder is recycled back into the powder hopper, where it is mixed with as-received powder. As more parts are made and more recovered powder is added to the hopper, the ratio of virgin to recovered powder may change. The recovery and reuse of powder for high-value materials like Inconel 718 has both economic and environmental benefits, but it is only safe and appropriate if the parts made with the recovered powder are identical to the parts made with virgin powder.

Mechanical testing of parts, while the benchmark for integrity, is destructive and time-consuming. Only a few parts can be tested as representatives of the entire lot. In contrast, X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) are fast non-destructive measurements that can be applied to both the powder and all parts. Problems in the recovered powder can be identified before it is recycled into the hopper; and every part can be quickly examined for consistent production.


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