Originally Posted by vapilot2004
I understand the coatings are ceramic with the nickel alloy at the core having a melt point several hundred degrees short of the temps seen in that stage of the engine.
I think that would be a misjudgment if true.
Most modern nickel-base alloys have a melting point above 900°C. If the temperatures exceed the melting point of the base alloy in the early stage of the LP turbine (IP turbine in RR jargon), the blades need to be air-cooled like what is done in the HP turbine. Certainly ceramic coatings can and do improve the temperature margin between the melting point of the alloy and the actual temperature of the air passing over the ceramic coating. Ceramic coatings are made up generally of four layers of differing materials. Ceramic TBC (thermal barrier coatings) fail through various degradation modes that include mechanical rumpling of the bond coat during thermal cyclic exposure, accelerated oxidation, hot corrosion and molten deposit degradation. There are also issues with oxidation. Sometimes, not well matched thermal expansion coefficients between the coating layers lead to coating cracking and coating failure. Areas of the ceramic TBCs can get stripped off, which reduces the life of the metal drastically, which leads to thermal fatigue and eventual failure.