Mechanism for Beneficial Effect of Y2O3 Dispersion for Protective Coating.

Although the beneficial effect of Y2O3 dispersion against high-temperature oxidation has been recognized for many years, the mechanism of the effect is still obscure. Our previous works suggest that dispersed Y2O3 suppresses spalling of Al2O3 coating layer by trapping a detrimental impurity element S within the bulk phase. In this work analytical electron microscopy gave a very important evidence for the S trapping on MA956-0.52Y2O3 alloy.Then it was found that the penetration of alloying constituents such as Mn, Cr into Al2O3 coating layer was extensively lowered on alloys doped with a moderate amount of Y2O3. This is considered another beneficial effect of Y2O3 dispersion.