We have studied the mechanism by which despersed Y2O3 exerts beneficia
l effects on the oxidation protection of an Al2O3 coating (film) on th
e basis of the following models: 1) Y2O3 suppresses surface segregatio
n of S by trapping it in the alloy matrix and accordingly suppresses s
palling of the Al2O3 film; 2.1) The diffusion of alloying elements int
o the Al2O3 film is retarded by dispersed oxide particles, probably th
rough formation of a diffusion barrier at the Al2O3/alloy interface; 2
.2) The diffusion in Al2O3 film is retarded through incorporation of Y
2O3 into the film 3)Y2O3 acts as an adhesive at the Al2O3/alloy interf
ace; 4) Y2O3 incorporated into the Al2O3 film suppresses the spalling
by increasing the plasticity of the film. We reached the following con
clusions: 1 is very important, 2 is also significant but 3 and 4 are n
egligible.