The PONI Research Group seeks to use advanced manufacturing processes to develop new materials and structures with enhanced mechanical properties. In particular, they are pursuing several exciting areas of exploration in solid-state materials processing: (1) Friction Stir Welding, (2) Cold Spray Deposition, and (3) Additive Friction Stir Deposition. As such, the PONI Research Group is a recognized leader in quantifying process-structure-property-performance of these advanced processing technologies. Specifically, they strive to uncover fundamental understanding of mechanisms that drive mechanical performance in order to ultimately design and predict superior materials and structures.
Friction Stir Welding
Joining of engineering materials continues to be an ongoing challenge in today’s manufacturing environment. The challenge is in part due to the use of new advanced material systems or traditionally hard-to-weld alloys. In addition, the desire to join dissimilar materials for lightweighting purposes and the environmental performance requirements have pressed engineers to explore new and innovative joining methods. However, non-ferrous alloys, dissimilar joints, and materials with advanced processing histories (i.e., advanced high strength steels) present significant barriers to traditional fusion joining methods. As such, friction stir welding (FSW) overcomes many of the problems associated with fusion welding including solidification cracking, residual stresses, liquid metal embrittlement, etc. While knowledge and expertise exists on the FSW process and relationship between welding parameters and sound joint fabrication, there still exists considerable knowledge gaps in understanding fundamental mechanisms of fatigue in FSW and how to predict performance. Towards this end, The PONI Research group seeks to characterize the relationship to microstructural features developed during processing and mechanical performance. Of particular interest has been on their work on FSW of lightweight metals including aluminum and magnesium alloys, and dissimilar metal joining. The extensive characterization of FSW of lightweight alloys by their group has led to the ongoing development of microstructure sensitive fatigue models adapted for FSW, which has been used to optimize industrial and DoD structural components to improve fatigue performance.
Cold Spray Deposition
Cold spray (CS) deposition is a solid-state material deposition process that uses the kinetic, rather than thermal, energy of the impacting particles to bond with the substrate. In the CS process, high pressure gas is expanded through a converging, diverging (de Laval) nozzle causing it to accelerate, and thus speeding up the suspended powder with it. While CS deposition has been used regularly for repairing wear and thin corrosion resistant coatings, The PONI Research Group is focusing on characterizing the mechanical behavior including the fatigue of free form additive like depositions of CS. In order to effectively characterize structural repairs in CS, the PONI Research group has developed a new approach to quantify the interfacial fracture toughness of CS deposits. Additionally, they have quantified the potential use of CS for structural repairs of corrosion damage, which could be used for life extension programs of aging aircraft. Towards this end, the PONI Research Group is currently establishing process-structure-property relationships in order to understand fundamental mechanisms critical for repair methods. In particular, they are focusing on key fundamental mechanisms of fatigue crack nucleation and propagation in the additive repairs.
Friction Stir Additive Manufacturing (FSAM)
Although many additive manufacturing (AM) processes rely on powder-based beam melting or sintering methods, recent innovations in solid-state AM approaches such as Friction Stir Additive Manufacturing (FSAM) provide unique capabilities to additively manufacture or repair alloys with wrought-like properties, while avoiding the liquid-solid phase transformation that can be problematic for certain metals such as aluminum and magnesium alloys. To produce additive components using the FSAM process, either a solid feedstock or chips are forced to flow through a hollow rotating tool on to a substrate and subsequent layer. The FSAM generates frictional heat and hydrostatic pressure so the deposited material undergoes shear-induced severe plastic deformation and dynamic recrystallization (DRX), which results in sub-micron equiaxed granular structures, and most importantly, achieves metallurgical bonding between the feedstock and substrate and subsequent deposition layers. This new materials processing and additive technology, which UA invested in with the purchase of a B8 Meld machine, has provided new opportunities to aid in the fundamental understanding of process mechanisms and related microstructure and mechanical behavior. The PONI Research Group, is a recognized leader in FSAM and focused on quantifying the fundamental process-control relationships for understanding of intrinsic mechanisms of the process. Their work has resulted in some of the first publications on this new technology on additive manufacturing of aluminum alloys including a recent publication demonstrating the use of the FSAM to recycle waste metal machine chips into AM builds with wrought like properties [read here]. In addition, the PONI Research Group is focusing on deposition of high temperature materials and magnesium alloys.
Current research projects:
- Recycling and Reuse of Metal Alloys by a Single Solid-State Additive Manufacturing and Repair Process
- Additive Repair via Cold Spray Deposition in Aluminum Load-Bearing Structures
- Microstructurally Small Fatigue Crack Growth in High Strength Aluminum Alloys
- Additive Friction Stir Deposition Process Development for Magnesium Alloys for Rotorcraft Applications
- Solid-State Additive Repair of High Hardness Steel Armor Plate
- Design of Lightweight, Light-Duty Expeditionary Airfield Surfacing Systems