Characterization of thick plasma spray tungsten coating on ferritic/martensitic steel F82H for high heat flux armor

Two types of plasma spray tungsten coatings on ferritic/martensitic steel F82H made by vacuum plasma spray technique (VPS) and air plasma spray technique (APS) were examined in this study to evaluate the possibility as plasma-facing armor. The VPS-W/F82H showed superior properties. The porosity of the VPS-W coatings was about 0.6% and most of the pores were smaller than 1-2 mu m and joining of W/F82H and W/W was fairly good. Thermal load tests indicated high potential of this coating as plasma-facing armor under thermal loading. In case of APS-W/F82H, however, porosity was 6% and thermal load properties were much worse than VPS-W/F82H. It is likely that surface oxidation during plasma spray process reduced joining properties. Remarkably, both coatings created soft ferrite interlayer after proper heat treatments probably due to high residual stress at the interfaces after the production. This indicates the potential function of the interlayer as stress relieve and possible high performance of such coating component under thermal loads. (C) 2009 Published by Elsevier B.V.