Abstract

Thermal barrier coatings (TBCs) for turbine airfoils in high-performance engines represent an advanced materials technology that has both performance and durability benefits.

Foremost of the TBC benefits is the reduction of heat transferred into air-cooled components. Other potential benefits include increased resistance to hot corrosion and oxidation. In order to achieve these benefits, however, the ceramic coating system must be reliable.

TBCs applied by physical vapor deposition (PVD) processes are currently tailored to achieve superior strain-tolerant microstructures which facilitate reliable operation in aircraft propulsion engines. In particular, the electron beam evaporation/physical vapor deposition (EB/PVD) process can produce ceramic coatings with a highly strain-tolerant columnar microstructure, which is well bonded to the oxidation resistant metallic layer of the system. Intercolumnar gaps between the ceramic grains reduce the effective modulus in the plane of the coating and permit ceramic-metal thermal expansion mismatch and thermal strains to be accomodated without producing large stresses.

Microstructures of EB/PVD coatings are being further modified to density the outer surface of the ceramic coating to achieve improvements in hot corrosion and erosion resistance for industrial-marine and aircraft gas turbine engine applications.

The impact of projected modifications of the PVD process aimed at achieving tailored ceramic coating microstructures is discussed from the perspective of ceramic coating lives achieved in burner rig tests. Predicted ceramic coating lives for specified engine-mission environments are also discussed.

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