Optimizing Plasma Spraying Process Parameters for Tungsten Coatings Used in Fusion Reactors

Abstract

The quality of low-pressure plasma-sprayed tungsten (W) coatings for application in fusion reactors was investigated under various spray process parameter settings for the following substrate materials: carbon fiber composite, Eurofer (a ferritic/martensitic steel with reduced activation), and tungsten. The deposited coatings with a thickness of approximately 130 µm were evaluated in terms of porosity, deposition efficiency, defects, and surface roughness. Selected parameter sets were applied to produce scaled-up coatings up to 500 µm in thickness on Eurofer and tungsten substrates. Regions of very low porosity of approx. 0.3% and varying grain appearance were found. However, the subsequent grain size evaluation in terms of the aspect ratio of the fitted ellipse and the maximum Feret diameter did not reveal any significant differences in grain structure through the coating regions. The residual stress measurements performed by XRD using the sin²(Ψ) method validated the thermal stresses within the coatings resulting from the thermal mismatch between the coating and the substrate during cooling. The results indicate that the process settings and spraying process were effective in reducing residual stresses and producing coatings suitable for future fusion-relevant applications.