If you talk about parts like turbine blades of the first stage of a gas turbine (900°C operating temperature), then you need a coating that protects the substrate from oxidation. There are not many solutions.
For inner surfaces of the blades, there is only one variant: aluminizing from gas phase (Ar+AlF).
For external surfaces there are three variants of oxidation protection coatings:
Coatings of MCrAlY (M = Fe, Ni or Co), applied by means of vacuum plasma spraying, HVOF or PVD. This coating is often used as a bond coat for a ceramic thermal barrier coating of YSZ.
Coatings of Pt/Al, applied by means of PVD (also with YSZ-top coat).
My coat Cr-Cr2O3, applied by means of high-velocity atmospheric plasma spraying (HV-APS).
Which of these coatings it better, is hard to say, because all have its advantages u disadvantages.