CAREER: In-situ Hybrid Layerwise Rolling and Sealing in Laser Powder-bed Fusion Manufacturing of Tungsten: Fundamental Processing Mechanisms and Transition Temperature Controls

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Refractory metals and alloys of extremely high melting temperatures, particularly tungsten (chemical symbol: W), offer great potential for applications in harsh environments found in the space, defense, and nuclear applications, etc. Additive manufacturing has been explored in the research and development of tungsten parts because of its ability to produce complex single-piece components along with reducing lead times and prototype costs. However, the inherent brittleness and high susceptibility to cracking of this material class pose major challenges to its production using high-temperature additive manufacturing such as laser powder-bed fusion (LPBF). This Faculty Early Career Development (CAREER) grant supports fundamental research that will generate knowledge related to a new hybrid manufacturing technique, combing in-situ rolling and sealing layer-by-layer during LPBF of W parts, capable of performing real-time modifications during the process, and thus, producing parts with controlled and improved properties. The research will enable knowledge-driven processing designs for the advanced production technology of W parts, which would open doors to new applications ranging from waveguides and collimators for hypersonic aircraft leading edges and plasma-facing components in unique fusion reactors, and thereby, create opportunities to strengthen the U.S. economy and national security. This project will also design and deliver intriguing hands-on educational and outreach experiences for the recruitment of diverse high school students to STEM majors and the retainment of undergraduate and graduate students from underserved groups, while ensuring their success in STEM-related careers or post-graduate education.The overarching goal of this CAREER award is to understand the mechanisms that govern the evolution of the structures and properties of W made by layerwise rolling and sealing in LPBF. The team will first investigate how plastic deformation and strengthening, induced by rolling and nanoparticle sealing, respectively, affect the thermodynamic driving forces and kinetics in W as well as impacts on structural evolution, while encountering process cycles of melting and re-melting. Experimental studies will include LPBF sample fabrications with in-situ rolling-sealing and materials characterization techniques. Crystal plasticity, discrete dislocation dynamics, and cellular automata models will be integrated to investigate into the evolution of dislocations, microstructure, and texture during the process. Next, the project will unveil the fundamental mechanisms underlying the newly achieved W structure and its role in the development of ductile-to-brittle transition and recrystallization. Fracture toughness testing will be conducted to investigate the ductile-to-brittle transition temperature, complemented by the crack-tip plasticity theory and thermo-kinetic analysis to discover their respective contributions to the transition temperature. Furthermore, annealing followed by microhardness testing will be employed to identify the recrystallization temperature, with recrystallization kinetic models and thermodynamic principles used to determine the recrystallization driving forces. Then, how the fabricated W structure influence deformation mechanisms and mechanical behavior will be elucidated through tensile testing up to fracture at different temperatures to evaluate the strength and ductility. In addition, the plastic behavior and its contributions toward strength and ductility will be studied using the modified Clyne model. The research findings will offer insights into the thermodynamic and kinetic aspects of the hybrid in-situ rolling-sealing LPBF and their influence on thermal and mechanical behaviors under various mechanical, nano-structural, and thermal constraints. Ultimately, the knowledge attained will enable the advancement of W materials through improving part performance and increasing the operating temperature limits.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.