Development of Plasma Sprayed Thermal Barrier Double Layered Coating for Gas Turbine Inner Casings

Thermal barrier coatings (TBCs), consisting of yitria-partially-stabilized zirconia (YSZ) topcoat and metallic bond coat, are mostly effective to protect the metallic components of the hot section of gas turbines against the high temperature environment. The aim of this work was to develop a unique thermal barrier coating process for application on the gas turbine huge inner casing. Aforementioned casing was the inlets nuzzle of hot air to the turbine chamber that is exposedto hot erosion in more than 800oC heat with about 3.5 meters length and 1.5 meters diameter. The coating process was accomplished by the application of NiCrAlY bond coating and YSZ top coating via plasma spraying method perfectly on the inner surface of the casing. The novelty of this work was the application of this double layered coating on the inner casing for the first time in Iran. The microstructural, microhardness and wear properties of the coatings werestudied. Results showed dense microstructures with porosity of less than 5 percent for the bond and more than 12 percent porosity for the top coatings that is conformed with TBC structures. The coatings provided high wear resistance. The adhesion strength of the coatings was measured about 25 MPa. The results revealed that the applied thermal barrier coatings were highly qualified for the inner casing application.

Development of Plasma Sprayed Thermal Barrier Double Layered Coating for Gas Turbine Inner Casings Keywords:

Thermal barrier coatings , inner casing , Gas turbine , Plasma spray