Vacuum plasma sprayed (VPS) tungsten (W) coatings hold great promise for plasma facing components in future fusion devices. However, the large coefficient of thermal expansion (CTE) mismatch between W and underlying structural steels poses a significant problem for manufacturing and service life because of the evolution of large thermally induced stresses leading to failure. In this paper both the concept of functionally graded material (FGM) W/steel interlayers and the use of steel substrate surfaces with regular surface sculptures of millimetre scale created by e-beam surface manipulation, termed surfi-sculpt and developed by TWI of the UK are investigated. The objective of these approaches is to enhance coating adhesion and to engineer macroscopic variations in the effective CTE through the thickness of the subsequently VPS deposited W coating. The effects of surface geometry on coating adhesion and microstructure have been investigated, and preliminary conclusions on the key surface sculpture geometrical features required for high adhesion dense W coatings have been identified.

Transferred-arc cleaning and roughening as discussed in the patent by Muhlberger is often used as a surface preparation method prior to low pressure plasma spray (LPPS) deposition of coatings. In this article, electrically transmitted arc cleaning is investigated as a precision cleaning method for thin films lubricating substrates as well as traditional cleaning and roughening for LPPS. A Box-Behnken reaction surface construction test is carried out with variation of the chamber pressure, the substrate distance and the torch current taking into account the transferred arc voltage, the voltage fluctuation, the current, the emitted light, and the surface cleanliness. The results of the analysis show the effect of the various independent quantities on the measured responses. Different stages in the cleaning process are determined by their sample cleanliness, their voltage level, their voltage fluctuation, their emitted light and their rate of erosion. Paper includes a German-language abstract.