Recyclability Study on Inconel 718 Powder and its Effect on Microstructure and High Cycle Fatigue of LPBF Components

Sadek, Alber

The powder quality is a crucial aspect of the AM process to guarantee the manufacturability and quality of the manufactured parts. Metallic powder alloys for AM must have a specific particle size and shape distribution in different AM processes, such as laser powder bed fusion (LPBF). However, the process produces leftover metal powder, often unused, resulting in significant cost and disposal overhead.

For these purposes, this study focuses on the possibility of recycled powder for Inconel 718 after many production cycles and on the influence of such build-cycles on the particle size distribution, morphology, and chemical composition. Inconel 718 parts made from virgin and 13 times reused powder were processed and characterized in as-built condition and after heat treatment. The effect of powder recycle times on the microstructure and high cycle fatigue properties of additively manufactured components was assessed. Results clearly show no significant difference in particle size distribution among the recycled powder samples analyzed. However, it was noted that there was a relatively small increase in the volume fraction of the particle size over 60 μm after Build 7. The spherical shape of the powder particle was affected significantly after the first build, and some particles were covered by partially molten material, which could affect its flowability. The flowability dropped by 26% after the first build and remained almost constant. The apparent density of the recycled powders and powder packing density were within accepted limits for powder usage. Both powders appeared to exhibit the same fatigue limit since the flat region is confirmed to be in the 10⁶-10⁷ cycle range. Only minor differences between the two investigated materials demonstrate the possibility of high-quality parts production from recycled powders, which in turn provides a pathway for significantly reducing powder consumption and, thus, costs during the LPBF process.