Investigation and kinetic study of TGO growth behavior in high-entropy alloy coating systems

Abstract

In this study, AlCoCrFeNiTi and AlCoCrFeNiZr high-entropy alloys (HEA) developed for high temperature applications were applied as topcoats of the coating system by atmospheric plasma spraying (APS) process, while CoNiCrAlY bond coats were coated by high velocity oxygen fuel (HVOF) technique. As a result of isothermal oxidation tests performed in the range of 1000 degrees C-1200 degrees C, both HEA systems were found to be resistant to oxidation. The rate constant (Kp) and activation energy (Q) values obtained at 1200 degrees C were calculated as 0.1090 mu m2/h/224.6 kJ/mol for AlCoCrFeNiTi and 0.1174 mu m2/h/230.2 kJ/mol for AlCoCrFeNiZr, respectively. The findings reveal that the growth kinetics and microstructural evolution of the TGO layer directly affect the oxidation-induced degradation behavior of composite coating systems. The findings indicate that oxidation-induced microstructural changes and the growth behavior of the TGO layer are determinants of coating degradation.