Sulfur segregation to oxide/metal interfaces: a comparison of thermally grown and plasma deposited Al{sub 2}O{sub 3}

Segregation of S to oxide/metal interfaces was studied using scanning Auger microscopy after removing the oxide film in ultrahigh vacuum. Two types of alumina films were investigated: one formed from oxidation at 1000 C on Fe-28at.%Al-5at.%Cr; the other was deposited on the same alloy via plasma synthesis, where Al was codeposited with O to form an amorphous Al2O3 film, 0.2 or 0.8 {mu}m thick. Subsequent heat treatment of the deposited film at 1000 C caused it to slowly transform to {alpha}-Al2O3, and the transformation took place at the film/alloy interface. S segregated to the interface during heat treatment. The amount increased with heat treatment time but was much less than that with scales formed by oxidation. Not all the film/alloy interfaces contained S; the behavior was different from the uniform S coverage found under thermally grown scales. S segregation to the film/alloy interface seems to be controlled by availability of interfacial sites rather than bulk diffusion rates