Preliminary Investigation into Dissolvable Supports for Additively Manufactured Inconel 718 Components

The proposed project will demonstrate dissolvable supports for Inconel 718 (IN718) components fabricated using selective laser melting (SLM) Powder Bed Fusion (PBF) Additive Manufacturing (AM). Currently, the types of metal components that can be fabricated using PBF are constrained by the requirement that supports be mechanically accessible. As a result, components with interior geometry, such as cooling channels or reentrant structures, often cannot be fabricated without compromising design. To overcome this issue, Dr. Hildreth at Arizona State University (ASU) recently demonstrated a dissolvable support process that seamlessly integrates with existing PBF printing technologies and processes.

The proposed project will generate an initial data set to assess how the dissolvable support process impacts mechanical properties, including tensile strength, high-cycle fatigue (HCF), and surface finish. This data set will be used to identity if and how processing parameters need to be modified along with how much additional research is needed before this technology could be integrated into PBF processing guidelines and used by NASA to improve device performance.

The project team consists of Dr. Owen Hildreth at ASU and Dr. Omar Mireles at NASA Marshal Space Flight Center (MSFC). NASA MSFC will supply Inconel 718 tensile specimens fabricated using PBF along with the necessary heat treatments to refine microstructure; metallurgical analysis; mechanical testing (tensile, high cycle fatigue); and a component with complex geometry (a stator). ASU will process Inconel 718 tensile specimens fabricated using PBF samples through their dissolvable support process. This includes sensitization, electrochemical etching, roughness measurements, optical imaging, and scanning electron microscopy imaging. Both ASU and NASA MSFC will gather metallurgical data (cross-section stain etching, x-ray diffraction) as necessary.

The proposed project will demonstrate the feasibility to dissolve IN718 supports structures produced by Selective Laser Melting (SLM) Additive Manufacturing (AM). AM can enable new design paradigms that optimize performance characteristics; unfortunately, metal AM is constrained by the challenges associated with support structure removal. Unlike polymer AM, where dissolvable supports have been commercially available for years, manual grinding and machining operations are required for metals AM. This requires that support be mechanically accessible while increasing costs. To address this issue, the ASU developed a novel approach that brings dissolvable supports to metals AM. The process and works by applying a sensitizing agent to areas of interest after build completion before the stress-relieving step. The sensitizing agent diffuses into the sample and alters the chemical composition of the top 100 – 200 µm of the sample surface. The “sensitized” region is highly susceptible to corrosion/dissolution such that the etching reaction self-terminates once the sensitized region is dissolved. As a result, the component separates from the support with less than 100 µm of material removed from the surface. Self-terminating sensitization requires only minor additions to the post-print annealing step and is not sensitive to component shape, working electrode shape, or their relative orientations. This process also reduces surface roughness from R_a = 16

µm to R_a = 4 µm. Support structures can now be removed from fluid accessible instead of mechanically accessible areas. Overall, this process has the potential to simplify post processing and reduce cost.

ASU’s dissolvable metal support technology bypasses this limitation without requiring any changes to the printing process itself. The proposed collaboration between ASU and NASA MSFC will generate the necessary mechanical data (tensile, high cycle fatigue) data and proof- of-capabilities (stator) to understand the impact that the sensitization and dissolution processes have on the component performance while also demonstrating its utility to support NASA’s mission of leveraging AM to improve system capability (through reduced weight, advanced design, etc.)

This project merges NASA MSFC’s expertise in Inconel 718 PBF processing, metallurgy, and mechanical testing, with ASU’s expertise in carburization and selective electrochemical dissolution. NASA will supply test specimens, collect metallurgical data, and run mechanical tests while ASU will conduct the support dissolution steps. The data generated through this project will be used to identify if and why the process impacts mechanical performance; how long a support dissolution process would take for a typical component; and how effective the process is at removing trapped powder and supports while reducing surface roughness.

This project will support the development of dissolvable supports for IN718 components fabricated using SLM AM techniques. After printing specimens are submerged in a saturated aqueous sodium hexacyanoferrate solution. Next, the component is heated to high temperatures (> 700 ˚C) to drive the sensitizing agent into the top 50 – 100 µm of the component and supports structure surface. Typical support structures are 100 – 200 µm thick and become completely sensitized. Next, the supports are dissolved using electrochemical processes designed selectively dissolve the sensitized regions while keeping the base component material cathodically protected. Since only sensitized region are dissolved, the component looses only a small amount of material even over excessively long etch times.

This is early/mid-stage (TRL 2) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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