This project plans for a transformative high deposition rate solid-state additive manufacturing process, Additive Friction Stir Deposition (AFS-D), to repair structural load bearing components on advanced generation five and future aircraft structural components. In this research, the project team plans to rapidly repair corrosion and mechanically damaged high strength aluminum alloy components through a solid-state layer-by-layer metal deposition process. In particular, the project team anticipates that through a combined materials science and solid mechanics approach, understanding of the fundamental mechanisms of a novel solid-state additive manufacturing process will facilitate the restoration of damaged components to original equipment manufacturers chemical and mechanical properties. In this project, the project team will focus on restoring bulk damage to structural flight components due to: a) galvanic corrosion, b) mechanical fatigue. Additionally, the AFS-D repair methodology will not require hazardous materials or create hazardous materials and does not increase any operational risk to the asset or the Warfighter. In fact, the repair technology is International Organization for Standardization container transportable, has low energy demands, operates in open atmosphere process, and can perform repairs at depots or in field for Point-of-Need manufacturing and repair.
This research will develop a roadmap for using AFS-D for repair and refurbishment in weight-critical applications by systematically investigating the effect of microstructural evolution and macroscopic repair geometry on fatigue and corrosion mechanisms in AA7xxx series aluminum alloys. This collaborative effort involves a multidisciplinary team with a combined skill set of processing science, microstructural characterization, and mechanical testing. The three-year research program is divided into four main complimentary technical tasks.
Task 1 will seek to systematically quantify the role of increasing plastic strain, strain rate, and temperature generation during processing to understand the physics of constituent-segregation, texture evolution, dynamic recrystallization, and grain refinement in high strength aerospace aluminum alloys.
Task 2 will elucidate how the AFS-D processing parameters influence structural evolution across multiple length scales fabricating fully-dense bulk deposits and repairs. To ascertain these effects, the research team will perform a comprehensive computational and experimental characterization study. The experimental approach will characterize the repair deposits from the nano- to the macroscale. In addition, the research team will simulate the AFS-D process using a smoothed particle hydrodynamics method to calculate the temperatures, material flow pattern, and stress state. Furthermore, phase field simulations will be conducted to model the evolution of the precipitate phase and crystal plasticity simulations will be used to elucidate the effect of shear-induced interfacial heating and severe plastic deformation on texture evolution during AFS-D processing.
In Task 3, the static and fatigue properties will be quantified to understand the dominant intrinsic and extrinsic structural features of repairs made with AFS-D. Furthermore, the relationship between AFS-D generated microstructures, localized corrosion mechanisms, and atmospheric corrosion behavior of AA7050 will be quantified.
Lastly, in Task 4, a lifecycle sustainability analysis using a five-step methodology will be performed to evaluate potential impacts associated with costs, ecosystem quality, human health, and resource availability that will help mature the solid state AFS-D process for repairing 5th generation aircraft.
The Joint Services and scientific community will benefit from the new knowledge and science related to the influence of AFS-D processing conditions for repair applications, specifically substrate cooling interactions with material feed rate, and processing forces for microstructural evolution correlated to monotonic, cyclic, and corrosion behavior that allow for determination of the constitutive behavior relations (static, fatigue, and corrosion) for AA7050. This fundamental research will assist in solving the technical gaps necessary for additive repair of aluminum alloys of mission critical components. Specifically, for the AFS-D repair of assets, the repaired component qualification presents new challenges related to material property requirements. The process modeling developed in this program is critical for a balanced effort in the physical and virtual (i.e. computer aided) digitally driven manufacturing approach to understand the process influence on thermomechanical history in the layer-by-layer deposition process to predict component performance.