Thermal barrier coating
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Thermal barrier coatings are layered systems applied to metallic surfaces, such as gas turbine or aero-engine parts operating at elevated temperatures. The principle use of TBCs are to insulate metallic components from large and prolonged heat loads. These coatings are produced with thermally insulating materials which can sustain an appreciable temperature difference between the load bearing alloys and the coating surface.[1] Thermal barrier coatings serve two main functions:
- Lowers the operating temperature of the structural metal and extends the life of components by reducing oxidation and thermal fatigue
- Allows engines to run at higher temperatures which improves efficiency.
[edit] Anatomy
TBCs have a duplex structure, with a ceramic coating on top followed by a metallic bond coat, which adheres the ceramic coat to the metallic substrate highlighted for protection. The ceramic coating is typically made of yttria stabilized zirconia (YSZ) which is desirable for having low conductivity. The metallic bond coat creates a contact between the ceramic coat and substrate. In addition, it protects the substrate from thermal oxidation and corrosion.
A new generation of TBCs are being manufactured that feature an additional layer above the top coat. These layers have similar thermal properties as the YSZ (Yttria partially stabilized Zirconia) and aim to further increase the energy efficiency of power engines. Promising material for this new layer include: zirconates, hafnates, and rare earth metals.
[edit] Processing
In industry, thermal barrier coatings are produced in a number of ways:
- Electron Beam Physical Vapor Deposition: EBPVD
- Air Plasma Spray
- Direct Vapor Deposition
[edit] References
- ^ F.Yu and T.D.Bennett (2005). J.Appl.Phys.97,013520 (2005)
T. Wakui, J. Malzbender, R. W. Steinbrech, Strain Analysis of Plasma-Sprayed Thermal Barrier Coatings Under Mechanical Stress, J. Thermal Spray. 13 (2004) 390.
