Additive Friction Stir Deposition of Aluminum Alloys and Functionally Graded Structures

State-of-the-art additive manufacturing technologies for metal parts have evolved around powder metallurgy and fusion welding-based processes. Both of these processing methodologies yield parts with inferior mechanical and physical properties as compared to wrought metal of the same composition. Additionally, the production rates for even the fastest processes are relatively low (~40 lbs/hr for Ti) and the part envelopes are limited to a few cubic feet. Aeroprobe proposes a highly scalable process for additive manufacturing of wrought metal structures based on their additive friction stir (AFS) process which provides high-strength coatings and welds (strengths comparable to the base metal UTS) while retaining a wrought microstructure. AFS has successfully deposited materials ranging from light metals, such as Al and Mg alloys, to high-temperature metals, such as Inconel 625 and oxide dispersion strengthened steels. Initial additive manufacturing demonstrations with AFS were highly successful and produced fully dense structures with wrought mechanical properties. The overall objective of this project is to further develop AFS technology into an additive manufacturing process to enable full-density, near net-shape fabrication of airframe structures. An initial process-structure-property relationship study will be conducted to demonstrate the physical and mechanical properties achievable in Al alloys via AFS. Finally, Aeroprobe will demonstrate the feasibility of AFS to produce complex 3D structures by fabricating an aluminum demonstration part of a relevant geometry.

Additive manufacturing via AFS has the potential to lower the cost and improve the performance of NASA airframes and spacecraft. Additive manufacturing via AFS also offers the potential to locally control the composition of a component, thus allowing for minimization of stress concentrations which can drive materials selection and design in fatigue-driven applications such as airframes. Lowering the buy-to-fly ratio is often attributed to subtractive manufacturing of webbed and ribbed components to reduce the structural weight while maintaining required stiffness. Manufacturing such components using additive manufacturing could drastically reduce extensive machining, excessive materials, the associated energy, and custom tooling costs. Using AFS to additively manufacture webbed and ribbed components on NASA airframes has the potential reduce total airframe cost through the mechanism mentioned above and with the added benefit having wrought material properties and performance.

The primary applications for early adoption of AFS are high-value propositions for which AFS enables some performance that is not achievable by traditional processing methods. One of the key benefits of AFS is that consolidation and deposition occur in the solid-state, thus highly engineered microstructures can be retained throughout processing. For, example AFS is being applied to large-plate and component manufacturing using ultra-fine-grained (UFG) Mg. Fabrication of UFG Mg components at a large-scale is currently not feasible and AFS is proving to make this possible. AFS is also being applied to coating and part fabrication using oxide dispersion strengthened alloys for fast-reactor nuclear power generation. Other commercial applications of AFS under development include coating of shaft journals for use in extreme wear and corrosion applications.

This is early/mid-stage (TRL 6) — 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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