The Role of Laser Texturing in Improving the Adhesion of Plasma Sprayed Tungsten Coatings

Abstract

Plasma sprayed W-based coatings have the potential application as joining interlayers for the plasma-facing components of future fusion reactors. Particularly in the form of tungsten-steel functionally graded materials (FGMs), they would reduce the stress concentration between the W-based plasma-facing armor and steel-based construction. For mechanical integrity, good adhesion is essential. For this, conventional grit blasting treatment of the substrate may not be sufficient. Therefore, alternative treatments capable of reaching significantly higher roughness without damaging the substrate are sought. In this study, the effects of laser texturing on the adhesion of plasma sprayed W and W-steel FGMs on W and steel substrates are investigated. A variety of surface profiles were achieved by controlled laser ablation in several types of patterns. Their geometric features were systematically varied and measured, and the extent of their filling by the coating material was evaluated. On the most promising patterns, coating adhesion tests were performed in shear loading mode and the best performing patterns were identified. Significant improvement over grit-blasted surface was obtained on patterned surfaces with a high effective contact area, promoting mechanical interlocking. On steel substrates, generally higher adhesion was observed, surpassing already the coating cohesive strength; this is attributed to a combination of mechanical interlocking and metallurgical bonding.