CTE

Firstly as it is a thermal barrier, then the thermal conductivity of the selected barrier coating material should be low.

Secondly since it is a coating, it therefore clear that it is being grown/deposited on some other material.

When two layered materials are grown on one another, then thermal expansion coefficients, adhesion and integrity of the layers upon repeated thermal cycling is important. to maintain strong adhesion and a longer life time for the TBC you need good inter diffusion at the interface between the two materials.

The substrate must not fail mechanically, and should provide a good reactivity to the the TBC material to form a good bond.

K. Sreenivas

Creep strength of the substrate is one important criteria. I would recommend the paper by F. Riallant et al. Met. Mat. Trans. A, 2014 on this aspect.

Considering the TMF properties, an alloy showing high yield strength below 700-800°C is another important criteria to avoid strain localization (see e.g. Papers by V. Maurel et al.). Generally alloys with high gamma prime stacking fault energies are recommended for this.

Finally, alloys stable with respect to TCP precipitation and not very sensitive to recristallisation after sand blasting are welcomed !

This will depend on the part and its loading during operation.

1)       The substrate has to be fit for purpose such that it does not fail before the TBC. On rotating parts it can mean creep strength, TMF lifetime… On combustor parts it is nearly irrelevant and a solution strengthened superalloys will be sufficient

2)       It has to be bondcoat compatible. This means that it has not to consume to much of the bondcoat by interdiffusion, and it has not to contaminate to much the bondcoat with elements leading to accelerated oxidation/corrosion

3)       It has to minimize the thermal stresses on the TBC, meaning an as close match as possible to the TBC CTE.

In fact there are many good solutions, one thing is that there are some bondcoat that are specifically designed for one substrate such to tackle the point 2).

Suggest the following paper:

https://www.sciencedirect.com/science/article/abs/pii/S0925838818307771