Analysis of TiC and TiN coatings exposed to fusion plasmas

TiC and TiN coatings on Mo and graphite substrates have been exposed to the divertor plasma in the ASDEX tokamak. The wall marked interaction was detected within the 20 mm wide region of the plasma scrape-off layer. Melted spots appear on the coatings, and, in the case of the Mo substrate, blistering and peeling was observed. Analysis after plasma exposure of a TiN coating on Mo, by auger electron spectroscopy and sputtering with 1 keV Ar+ ions, gave a depth profile showing depletion of N to a certain depth. Comparison is made with well defined ion bombardment effects on identical samples exposed to 1 keV H2+ ions. The possible origin of overlayer deposits of impurity atoms (S,O, Fe, C) on exposed samples is discussed. (author)