Compositionally Graded Transition from Tungsten to Ferritic-Martensitic Steels via Directed Energy Deposition for Fusion Reactors

Nuclear fusion reactors utilize W and W-based alloys as plasma-facing components, which require joining into steel cooling structures based on state-of-art divertor designs. Direct joining between W and steels leads to the formation of brittle intermetallics. Joining with filler alloys is not compatible with high-temperature applications as the microstructure may degrade and promote a critical failure. The directed energy deposition technique enables the deposition of multiple pre-alloy or elemental powders simultaneously, in a layer-by-layer fashion, with precise control of the composition to avoid the formation of intermetallic or detrimental phases. In addition, its ability to fabricate compositionally graded transitions reduces the coefficient of thermal expansion mismatch between adjacent interlayer alloys. In this study, we demonstrated a framework to optimize the processing parameters for each alloy, generated processability maps, and successfully fabricated a dense, multilayered, linear compositional gradient from W to Gr91 steel, using V-based and Fe-based alloys as transition elements. Microstructure and mechanical properties of the interlayers and the thermal cycling response of the gradient structure will be presented.