Speaker
Description
Fabrication of first wall components for Fusion Pilot Plants (FPPs) through conventional powder metallurgy routes may be unfeasible due to cost and durability concerns. Instead, technologies such as additive manufacturing could be used to produce near net shape components with specifically-tailored microstructures. Cold spray deposition is another strategy that can be used to produce thick (>100µm) refractory metal coatings on a variety of substrates, which could provide a viable path for the large-scale manufacture of resilient plasma-facing components (PFCs) [1].
To investigate the performance of these materials under fusion-relevant conditions, additively manufactured pure tungsten, cold spray pure tantalum coatings – approximately 200 μm thick on 316 stainless steel substrates – and conventionally manufactured pure W and Ta specimens were exposed to plasmas using the Divertor Material Evaluation System (DiMES) in the lower divertor at the DIII-D tokamak. Deuterium plasma exposures produced incident heat fluxes of 1.4-1.6 MW/m2 (inter-ELM) and 3.5-4 MW/m2 (ELM) during 6 shots of H-mode. Specimens were characterized with laser scanning confocal microscopy (LSCM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) before and after exposure.
The surface roughness (Sa) of all specimens increased post plasma exposure, with cold spray tantalum coatings also exhibiting growth of existing, and formation of new, surface pits, approximately 30µm in size. SEM imaging of conventionally and additively manufactured tungsten specimens shows the presence of surface particles, with diameter <1µm, which do not appear to contain carbon, according to EDS analysis. However, all specimens did exhibit carbon deposition in fiducial markers and other sub-surface features. SEM imaging also reveals the formation of surface cracking in the additively manufactured tungsten specimens, which will be investigated further through electron backscattered diffraction (EBSD). XRD reports no noticeable changes between pre- and post-exposure for all specimens. XPS shows the presence of surface oxides on all samples, which are observed to change in stoichiometry post exposure, potentially due to contamination, sputtering and/or D implantation [1].
These findings represent a key step toward validating additively manufactured and cold-sprayed coatings as viable solutions for next-generation plasma-facing components in fusion reactors.
This work was supported by US DOE under DE-NA0003525, DE-AC02-09CH11466, DE-FC02-04ER54698, DE-AC05-00OR22725, DE-AC52-07NA27344 and DE-SC00020428.
[1] Ialovega et al. ‘Initial study on thermal stability of cold spray tantalum coating irradiated with deuterium for fusion applications‘ Phys. Scr. 98 (2023) 115611