Electrode erosion mechanism in the rod plasma injector type of generator as deduced from the structure of irradiated substrates

Titanium atoms were alloyed into a polycrystalline alundum substrate using a various number of intense pulses consisting of plasma of the working gas and vapor and low energy ions of Ti eroded from electrodes of the rod plasma injector type generator. It appears that at a single pulse titanium always forms a thin metallic film not mixed with the substrate material. With increasing number of pulses the amount of titanium atoms mixed into the substrate increases, whereas the thickness of the film - decreases. Analyses of phase composition and of structural properties, as well as computer simulations of thermal evolution brought the present authors to the conclusion that increase of number of pulses leads to decrease of melting temperature of the top layer of the substrate. It has also been confirmed that metallic ions eroded from electrodes do not undergo such acceleration like working gas ions do; their energy remains on the 200-300 eV level. It is concluded that erosion of the electrode material occurs during the last phase of the discharge via the vacuum arc mechanism.