High Temperature Electron Beam Additive Manufacturing of Tungsten Plasma Facing Components with Integrated Porous Armor

Statement of Problem: Cost-effective materials and manufacturing are crucial towards realization of many large- scale human endeavors including space exploration and understanding the origins of the Big Bang. For grid-scale fusion, robust and durable divertors with a large heat removal capability, robust mechanical properties, low sputtering yield and transient plasma damage tolerance must be developed. Scalable production methods are also needed, as these parts will be replaced during a fusion plant lifetime. Technical Approach: Additive Manufacturing (AM) is rapidly changing the way heat transfer devices are designed and manufactured, reducing complex assemblies to monolithic structures. AM tungsten lattices with location specific design features could act as thermal shock absorbers, alleviating some of the concerns regarding plasma transients on fusion divertors. We propose to print a solid, near-net shape, pure W thimble with a metallurgically bonded lattice armor using Electron Beam Powder Bed Fusion (EB-PBF). The combination of high power beam, vacuum processing and controlled heating/cooling are well suited to printing clean, crack-free tungsten above the ductile-to-brittle-transition temperature with reduced thermomechanical stress. Phase I results: We demonstrated the ability to print full-density(99.9%), centimeters scale tungsten solids and lattices using a highly customized, first-generation electron beam printer. Our material demonstrates high temperature ductility during 4-point bending and near-equiaxed microstructure. We also investigated various allied technologies related to tungsten including spark plasma sintering, bead-on-plate welding, powder qualification, material testing and post-processing (machining, finishing, brazing). We performed high heat flux arc-jet testing of commercially available, niobium 3D printed lattices; demonstrating the design and material opportunities enabled by technologically mature additive technologies. Phase II plans: We will upgrade the newest generation electron beam printer to be compatible with the tungsten process parameters developed in Phase 1, including a tungsten-specific modular print tank, multi-layer radiation shielding, active water cooling and in-vacuum gas plumbing. This printer has a smaller spot size than our Phase I machine and in principle, will be able to generate finer lattice structures. We will also perform extensive material testing including elevated temperature 4-point bending, vacuum leak testing, SEM analysis, plasma arc-jet testing at UCLA-HEFTY and plasma material interaction(PMI) testing at UCSD-PISCES. The final deliverable in Phase II will be a 3D printed tungsten cup with a metallurgically bonded lattice vacuum-brazed hermetic flange. This assembly will be installed back into same electron beam printer and cyclic electron beam testing with low-flow gas cooling will be performed. Commercial Applications and Other benefits: Batch production of tungsten fusion components using additive manufacturing could simplify fabrication while enabling more complex power plant architectures. Similarly, printing tungsten heat transfer components with integrated cooling could have significant applications in other fields such as medical imaging, radiation oncology and hypersonic vehicles.