Evaluation of Alternative Nickel Based Superalloys for Additive Manufacturing of Liquid Rocket Engine Components

NASA has a particular and immediate need to evaluate materials and processes for reducing the cost and improving component performance of Liquid Rocket Engines (LRE). This provides an opportunity to insert new materials as well as manufacturing processes such as additive manufacturing (AM) into the engine fabrication or production upgrades. While heritage processing of LRE components relied on stainless steels (SS) and Nickel based superalloys, more recent studies have identified the HR-1 as potential game changer since this materials meets the needs of a multitude of LRE component requirements. Thus by developing fundamental standards for AM fabrication and post build processes specific to this material, the development costs can be greatly reduced by concentrating efforts on one material rather than individual materials for each component.

Various AM processes are being evaluated for liquid rocket engines including Laser Powder Bed Fusion (L-PBF) for printing smaller monolithic components, and blown powder directed energy deposition (DED) for other larger components. Common to all these processes is the selection of alloys in powder form. Metal powder is used in both SLM and DED AM processes as the feed stock with their complimentary use of 45 m and 140 m diameter powder, respectively. Thus development of AM processes and post processing heat treatments for one given Ni based superalloy would streamline the development tasks for material development and reduce development costs.

Commonality in the material selection greatly streamlines the qualification testing required thereby reducing cost and schedule impact. As new materials and processing methods become available it is imperative to re-evaluate available materials for fabrication LRE components.

Selection of materials for use in LREs consider:

• • Increased strength and increased conductivity without loss of ductility.
  • Thermo-mechanical fatigue resistant.
  • Resistance to hydrogen embrittlement.
  • Availability in a variety of forms, which are weldable.
  • CTE match with Cu alloys used in the regenerative cooled components

(CTE of C18150=16.5 µm/m-°C)

As Table I shows, there are improvements to be obtained by switching from the Inconel alloys with their low coefficient of thermal expansion (CTE) to alloys with higher values such as HR-1. This is a critical parameter in bi-metallic joints since it drives the localized stresses resulting in low cycle fatigue (LCF) issues.

Initial evaluation will focus on the following objectives:

1) Evaluate virgin powder, recycled powder, as-built specimens and post heat treated specimens. This will validate the stability of the alloying elements during AM processes of both SLM and DED.

2) Conduct metallurgical and mechanical evaluation of samples built with SLM and DED. This will include microscopy in addition to tensile testing.

3) Evaluate heat treatment parameters on the resulting property and microstructural development.

Powders have been obtained for two Ni based superalloys of interest, NASA HR-1 and JBK-75. This provides a baseline of the starting powders for evaluation of SLM and DED specimens to determine elemental stability and possible contamination.

This study builds off earlier lessons learned in which minor elements were shown to affect the microstructural evolution doing post AM printing heat treatments and hence mechanical properties. Microstructural characterization of the SLM and DED specimens from HR-1 and JBK-75 will be correlated with tensile testing.

Teaming the NASA-MSFC with efforts by Dr. Schneider at UAH provides fundamental research for advancing these technologies. Once the material properties and processing are proven and validated, teaming arrangements with commercial business partners can manifest the path for maturation, commercialization, and insertion into industry. The type of research proposed in this study is needed to advance this technology from its current TRL of 1-3 to pre-production TRL of 4. Additional advancements in this technology would be achieved by successful component development and hot fire tests.

This is early/mid-stage (TRL 3) — 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.

None of these are guaranteed paths for this specific project — TechPort itself doesn't have an "apply" button. Reaching out to the contact(s) above with a specific question is usually the fastest way to find out what's actually open.