The use of APS thermal barrier coatings in corrosive environments

Thermal barrier coatings (TBC) can be used to reduce the metal temperature of gas turbine blades enabling higher Cr alloys (lower strength) to be used when gas turbines are to be used in corrosive environments (where hot corrosion resistance is required). However, the TBC must also be resistant to the corrosive environment and remain attached to the blade. A 1000 h test to evaluate air plasma-sprayed (APS) TBC adhesion to a low-pressure plasma-sprayed CoNiCrAlY bond coat (with and without through thickness cracking) under hot corrosion conditions at 850 °C has been carried out. The APS TBC significantly reduced the hot corrosion rate of the CoNiCrAlY; however, delamination cracking occurred with a thinner thermally grown oxide than would be expected from isothermal and cyclic oxidation testing.