Abstract:
Thermal Barrier Coating (TBC) are an integral part of present-day gas turbines for
both power generation and aerospace applications. TBCs consist of a top coat
(ceramic) and a bond coat which are deposited on top of a superalloy substrate to
withstand high temperatures, corrosion, oxidation and stress conditions. During the
high temperature exposure, an oxide layer starts to grow between the bond coat & the
ceramic top coat which is called as thermally grown oxide (TGO). Composition and
morphology of TGO plays a very vital role in improving the lifetime of a TBC system,
and is dependent on the bond coat composition. In this study, high entropy stabilized
bond coat will be deposited and tested for the bond coat in a TBC system. High entropy
materials are one of the latest developed material systems which consist of 4 or more
elements present in equi-atomic compositions. High configurational entropy of these
materials helps them to achieve greater stability at elevated temperatures. In addition,
these materials show sluggish diffusion effect which is beneficial in bond coats to
reduce the diffusion of different elements from the metallic superalloy substrate to the
TGO.
In the present study, high entropy- based bond coat will be developed by adding Ni,
Co, Cr, Fe and Al in near equi-atomic compositions. Effect of process parameters
along with post-deposition annealing on the microstructure of bond coats and the
resulting thermally grown oxide will be investigated. In addition, some minor
additions of refractory elements could be made to further tailor the TGO composition
to achieve longer lifetime of TBC systems. The testing of TBC systems will be carried
out at temperature of around 1000°C. Gas turbines used for power generation
applications usually experience such isothermal conditions where the TBC systems
deposited on the gas turbine blades have to withstand such high temperatures for
longer period of time. The TBC system deposited in this study will be characterized in
the as-coated condition and after testing at 1000°C for 5, 15, 50 and 100hrs.
