CAREER: Wire Arc Additive Manufacturing of Molybdenum Alloys for High-temperature Applications: Residual Stresses and Porosity Considering Ductile-to-brittle Transition Temperature

Refractory metals such as Molybdenum (Mo) based alloys have a great potential for applications in harsh environments, because of their high melting point. However, Mo alloys have several inherent drawbacks such as low ductility and a tendency of oxidation and cracking, which are adversely augmented when they are produced by additive manufacturing, due to non-equilibrium processing phenomena. This results in several complex technical blockades that hinder a broader adoption of additive manufacturing of Mo alloys in the industry. This Faculty Early Career Development (CAREER) project aims at fundamental research of wire arc additive manufacturing (WAAM) for Mo alloy structures, and will explore and elucidate the root causes of processing defects and their effects on part thermomechanical performance. If successful, the research will directly impact the Nation’s economic welfare and energy security. For example, the energy efficiency of land-based power plants could be improved and their carbon footprint decreased by using Mo alloys for turbine blades. In addition, the project will enhance the existing manufacturing curricula with data analytics components, provide undergraduate/graduate student with internship opportunities at national laboratories, and run hands-on manufacturing experiences for K-12 students. The outreach activities will enhance the education and training of next-generation STEM leaders in advanced manufacturing and foster inclusions of underrepresented groups. The overarching research goal of this CAREER award is to understand the underlying mechanisms of process-induced residual stresses as well as pore generation and investigate thermomechanical performances of WAAM processed Mo-alloy structures, focusing on titanium-zirconium-molybdenum alloys. The core research challenges lie on the lack of data in the physicochemical properties and complex defects development from non-equilibrium thermal cycles in layer-by-layer stacking. A combination of computational and physics-informed, data-driven models will be pursued for process understanding with experimental verifications and validations, including multi-scale material characterizations, process imaging and fatigue testing, etc. The research is expected to gain fundamental knowledge of the residual stress development and pore formation while considering the ductile-to-brittle transition temperature, and elucidate the deformation behaviors and thermomechanical performances from room to elevated temperatures, as correlated with heterogeneous microstructures, pores and oxidation. In addition, the project intends to establish a quantitative relationship between the process, signature, microstructure, property and performance, called the “design rule,” for WAAM that will ensure satisfactory fabrications of refractory alloy structures. The linkage may serve as an effective tool to potentially tailor microstructures and properties of WAAM structures with controlled and improved thermomechanical performance of final products. 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.