Thermal barrier coating

Thermal barrier coatings are highly advanced material systems applied to metallic surfaces, such as gas turbine or aero-engine parts, operating at elevated temperatures. These coatings serve to insulate metallic components from large and prolonged heat loads by utilizing thermally insulating materials which can sustain an appreciable temperature difference between the load bearing alloys and the coating surface.^[1]. In doing so, these coatings can allow for higher operating temperatures while limiting the thermal exposure of structural components, extending part life by reducing oxidation and thermal fatigue. In fact, in conjunction with active film cooling, TBCs permit flame temperatures higher than the melting point of the metal airfoil in some turbine applications.

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Anatomy

TBCs have a duplex structure, with a ceramic coating on top of a metallic bond coat. The ceramic coating is typically made of yttria stabilized zirconia (YSZ) which is desirable for having very low conductivity while remaining stable at nominal operating temperatures typically seen in applications. The metallic bond coat creates a superior bond between the ceramic coat and substrate, facilitating increased cyclic life while protecting the substrate from thermal oxidation and corrosion.

Processing

In industry, thermal barrier coatings are produced in a number of ways:

• Electrostatic Spray Assisted Vapour Deposition ESAVD
• Electron Beam Physical Vapor Deposition: EBPVD
• Air Plasma Spray
• Direct Vapor Deposition

Additionally, the development of advanced coatings and processing methods is a field of active research. One such example is the Solution precursor plasma spray process which has been used to create TBCs with some of the lowest reported thermal conductivities while not sacrificing thermal cyclic durability.

References

• Institute for Materials and Processes in Energy Systems (IWV)

1. ^ F.Yu and T.D.Bennett (2005). J.Appl.Phys.97,013520 (2005)

V.kurup, A.prasad, D.parab, R.thosar of Plasma-Sprayed Thermal Barrier Coatings Under Mechanical Stress, J. Thermal Spray. 13 (2004) 390.