We have studied the mechanism by which dispersed Y 2 0 3 exerts beneficial effects on the oxidation protection of an A1203 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 A1203 film; 2.1) The diffusion of alloying elements into the N2o3 film is retarded by dispersed oxide particles, probably through formation of a diffusion barrier at the A1203/alloy interface; 2.2) The

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... diffusion in A2O3 film is retarded through incorporation of Y2O3 into the film; 3) Y 2 0 3 acts as an adhesive at theA1203/alloyinterface; 4) YpO3 incorporated into the A2O3 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.