Thermal barrier coating experience in gas turbine engines at Pratt & Whitney |
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Authors: | S Bose J DeMasi-Marcin |
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Affiliation: | (1) Pratt & Whitney, 06108 East Hartford, CT, USA |
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Abstract: | Pratt & Whitney has accumulated more than three decades of experience with thermal barrier coatings (TBCs). These coatings
were originally developed to reduce surface temperatures of combustors of JT8D gas turbine engines to increase the thermal
fatigue life of the components. Continual improvements in de-sign, processing, and properties of TBCs have extended their
applications to other turbine components, such as vanes, vane platforms, and blades, with attendant increases in performance
and component du-rability. Plasma-spray-based generation I (Gen I) combustor TBCs with 7 wt % yttria partially stabilized
zirconia deposited by air plasma spray (APS) on an APS NiCoCrAlY bond coat continues to perform ex-tremely well in all product
line engines. Durability of this TBC has been further improved in Gen II TBCs for vanes by incorporating low-pressure chamber
plasma-sprayed NiCoCrAl Y as a bond coat. The modi-fication has improved TBC durability by a factor of 2.5 and altered the
failure mode from a “black fail-ure” within the bond coat to a “white failure” within the ceramic.
Further improvements have been accomplished by instituting a more strain-tolerant ceramic top layer with electron beam/physical
vapor deposition (EB-PVD) processing. This Gen III TBC has demonstrated exceptional performance on rotating airfoils in high-thrust-rated
engines, improving blade durability by three times through elimination of blade creep, fracture, and rumpling of metallic
coatings used for oxi-dation protection of the airfoil surfaces. A TBC durability model for plasma-sprayed as well as EB-PVD
systems is proposed that involves the accumulation of compressive stresses during cyclic thermal expo-sure. The model attempts
to correlate failure of the various TBCs with elements of their structure and its degradation with thermocyclic exposure. |
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Keywords: | EB-PVD gas turbine engine plasma spray TBC thermal barrier |
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