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Description
High-density (99.8%) electron beam powder bed fusion (EB-PBF) tungsten (W) has been successfully manufactured and deployed in plasma material interaction investigations that included DIII-D tokamak and Tritium Plasma Experiment (TPE) exposures. Since the tailored microstructure of EB-PBF W is fundamentally different from conventionally manufactured W, critical knowledge gaps were addressed such as thermal cycling, anisotropic thermal management, erosion properties, and fuel permeability mechanisms. EB-PBF offers distinct advantages over conventional processing, including reduced oxygen content, designing intricate geometries and controlling crystallographic textures through tuning the electron beam parameters.
Our experiments demonstrate that EB-PBF W with controlled crystallographic structures maintains structural integrity and erosion resistance comparable to manufactured W with the notable distinction that hydrogenic species preferentially occupy higher-energy defect sites. This suggests its promise as a candidate for plasma facing components (PFCs). EB-PBF-built W samples with dominant grain orientations, flat and angled geometry, and orientations to the AM build direction were exposed to DIII-D H-Modes with average surface heat fluxes of 36.5 MW/m² and 37.8 MW/m². Scanning electron microscopy revealed increased surface roughness on the samples after plasma exposure and migrated W was identified on the graphite sample holder, which both indicate erosion occurred. However, no substantial differences in material gross erosion rates were found between different grain orientations using visible W spectroscopy.
However, fuel retention could differ from conventionally manufactured W due to the distinct microstructure. A previous study revealed distinctive deuterium release in AM-W compared to typical traps in sintered W which suggests that retention may be due to trapping at high-energy defect sites, but at higher fluence retention could be more limited. After deuterium plasma exposure in TPE, thermal desorption spectroscopy identified distinctive desorption behavior compared to the conventional counterpart, likely arising from microstructural differences induced by varied textures. Higher temperature desorption in EB-PBF-built W relative to sintered W could point to a reduction in low energy trap sites but increased trapping in higher-energy defect sites consistent with past investigations.
Our work demonstrates that EB-PBF-built W exhibits only minor effects of crystallographic orientation on erosion and material integrity which highlights the potential of tailoring microstructure to minimize fuel retention, making it an attractive manufacturing process for PFCs.
This work is supported by US DOE under DE-FC02-04ER54698, DE-NA0003525, DE-AC02-09CH11466, DE-AC52-07NA27344.