Beneficial effects of Y₂O₃ dispersion on Al₂O₃ protective coating

Abstract
We have studied the mechanism by which dispersed Y₂O₃ exerts beneficial effects on the oxidation protection of an Al₂O₃ coating (film) on the basis of the following models : 1) Y₂O₃ suppresses surface segregation of S by trapping it in the alloy matrix and accordingly suppresses spalling of the Al₂O₃ film ; 2.1) The diffusion of alloying elements into the Al₂O₃ film is retarded by dispersed oxide particles, probably through formation of a diffusion barrier at the Al₂O₃/alloy interface ; 2.2) The diffusion in film is retarded through incorporation of Y₂O₃ into the film ; 3) Y₂O₃ acts as an adhesive at the Al₂O₃/alloy interface ; 4) Y₂O₃ incorporated into the film suppresses the spalling by increasing the plasticity of the film. We reached the following conclusions : 1 is very important, 2 is also significant but 3 and 4 are negligible.