Y2O3 Dispersion Effect on Al2O3 Protective Coating Examined on the Basis of Five Models

The mechanism by which ODS alloys are provided with excellent oxidation resistance remains still ambiguous. The ambiguity originates from a wide variety of scale features: pores, composition, stress etc. We used Al2O3 coating film prepared under a same condition in order to avoid the ambiguity and in addition to obtain fundamental information for the development of ceramic coating technique. This work was made on the basis of the following five models. I. Dispersed oxide suppresses the spalling of Al2O3 film through trapping a detrimental element S. II. ODS alloys form a diffusion barrier enriched in Y at the Al2O3 film/alloy interface and suppress the penetration of alloying elements into the film. III. The above barrier acts as an adhesive of Al2O3 to the substrate alloy. IV. Incorporation of Y into the Al2O3 film retards the diffusion of alloying elements within the film. V. The above incorporation of Y suppresses the spalling of Al2O3 film by increasing the plasticity of the film. We examined these models directly or by simulation experiment using Y2O3 undercoat as a barrier and an Al2O3 coating film doped with Y2O3. The following conclusions are reached: (1) Model I is the most important for suppressing the spalling of Al2O3 film. (2) Models II and IV have also remarkable importance for diffusion retardation. (3) Models III and V have minor importance.