Mitigating TGO growth with glass-ceramic based thermal barrier coatings for gas turbine applications

Thermally grown oxide (TGO) layer develops and grows at metal based bond coat (BC) and ceramic top coat (TC) interface of thermal barrier coating (TBC) system at elevated temperatures and mainly composed of aluminium oxides (Al2O3). In addition to providing efficient protection from oxidation and hot corrosion, TGO layer increases effective adhesion between BC and TC. Failure in TBC systems occurs by ceramic top coat spallation due to crack formation at top coat-TGO interface or bond coat-TGO interface due to abnormal progression of TGO layer. However, research is essential to derive an in-depth understanding of TBC system failure. This work investigated the oxidation behaviour of a typical TBC system fabricated by replacing conventional (MCrAlY) bond coat with glass-ceramic coating. Three TBC systems were developed: glass-ceramic bond coated TBC system, composite (15 wt% YSZ reinforced glass-ceramic) bond coated TBC system, and double layered bond coated (glass-ceramic coat and composite coat) TBC system with 8-YSZ top coat. Oxidation resistance was assessed through isothermal oxidation tests at 1000 degrees C for 100 h. Results indicated that all glass-ceramic based TBC systems exhibited promising oxidation resistance while triple layered TBC system showed the best performance. Microstuctural study showed the absence of detrimental TGO layer that made these coatings advantageous for high temperature applications.