Plasma deposition of high temperature protective coatings

Oxide ceramic films can be made using a vacuum arc based technique in which a metal plasma is formed in an oxygen background, with ion energy controlled by the application of a repetitive pulse bias to the substrate throughout the deposition. High ion energy early in the process produces atomic mixing at the film-substrate interface while lower but optimized ion energy later in the deposition can control the structure and morphology, and films that are adherent and dense can be formed in this way. In recent work we have investigated the formation of films of aluminum-silicon oxide on silicon carbide substrates by mixed aluminum and silicon plasmas produced from separate plasma sources. The Al to Si ratio was controlled by the plasma gun parameters, and the guns were pulsed simultaneously so as to mix the plasma streams before deposition; a magnetic multiple plasma homogenizer device was also used to further blend the two plasmas. Films with Al:Si ratios varying from 2:1 to 8:1 were produced in this study (Al:Si is 3:1 for Mullite), and the oxygen content in the films was controlled by varying the oxygen partial pressure during deposition. Additionally, we have compared some of the characteristics of alumina films plasma deposited on iron aluminide substrates with films produced by e-beam evaporation of Al{sub 2}O{sub 3} using oxygen ion beam assisted deposition onto unheated or heated substrates. Here we outline the film synthesis techniques and describe the characterization results obtained to-date