Development & Characterization of High Entropy Stabilized Bond Coat for Gas Turbine Blade Applications

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.