What sorts of considerations are important for the ceramic coating? I'd assume that the coating is not under the same types of stress as the alloy core, and so thermal properties would be more important. Is that true, or is load as much of a factor there too?
I'm not deeply aware of the specifics of the mechanical loads near the surface due to rotation. Generally the mandates are to match CTE between the substrate and surface as much as feasible, and to insert a "bond" layer to help that match.
The dominant concerns I am aware of are low thermal conductivity, thermal stability, and lack of chemical attack in the environments in question.
