Tungsten-steel composites and FGMs prepared by argon-shrouded plasma spraying

Tungsten is currently the main candidate plasma-facing material for future fusion reactors. For large part of the inner surface, the first wall, it is foreseen to be joined to steel-based structural components. Tungsten-steel composites and graded layers can serve as joining interlayers to reduce the stress concentration at the interface, originating from the different thermal and mechanical properties of tungsten and steel and temperature excursions. Plasma spraying is among the prospective technologies to fabricate such layers. In this work, tungsten-steel composites and functionally graded materials (FGMs) were prepared using high power hybrid water-argon plasma spraying system. Argon shrouding was applied to reduce the extent of in-flight oxidation of the molten particles. First, steel and tungsten coatings were prepared at a variety of process parameters and subjected to comprehensive characterization. Based on this, optimized parameters were selected for preparation of the composites and FGMs, and their structure, composition and thermal properties were characterized. Finally, hot isostatic pressing (HIP) was explored as a technique to improve the density and thermal conductivity of the coatings.