INVESTIGATION ON COATINGS OF TOKAMAK 1ST WALL MATERIALS AND OF THEIR BEHAVIOR AFTER EXPOSURE TO HYDROGEN-ATOMS

Stainless steel (AISI 321) samples have been exposed to thermal (0.2 eV) hydrogen atoms with flux densities up to 1015 cm-2 s-1 at a temperature of 320 K. Surface changes have been observed indicating embrittlement. The hardness has been found to increase by more than 20 % and pits and holes (≈ 107 cm-2) develop. This behaviour is explained as a consequence of large hydrogen pressures developing due to hydrogen oversaturation in the material. According to the theory this behaviour was not observed for SS 321 specimens coated with palladium. The theory is shortly reviewed, the experimental set up described and micrographs of the surfaces are shown. Consequences with respect to fusion devices are discussed. © 1979.