Evaluation of nanostructured bond coat in thermal barrier coating system with nano alumina layer during oxidation

Abstract

A thermal barrier coating (TBC) system usually consists of a ceramic top coat (yittria stabilized zirconia or YSZ) and a metallic bond coat (MCrAlY) (M = Ni, Co or mixture of these two) on the nickel-based superalloy as a substrate. A thermally grown oxide (TGO) layer can be easily formed on the bond coat which plays an important role in the spallation of TBC due to its growth during oxidation. Hence, the principal purpose of this research is to provide a new coating to significantly lessen the TGO growth and to suppress the growth of detrimental mixed oxides (CSNs) on the Al2O3 (TGO) layer during oxidation. Therefore, air plasma sprayed normal and nano TBC systems including, Inconel 738/normal NiCrAlY/normal YSZ, Inconel 738/normal NiCrAlY/normal YSZ/normal Al2O3, Inconel 738/nano NiCrAlY/normal YSZ, Inconel 738/nano NiCrAlY/normal YSZ/nano Al2O3 (as a novel system), and Inconel 738/normal NiCrAlY/nano YSZ were prepared then evaluated by pre-oxidation at 1000°C for 48h, high temperature oxidation at 1000°C for 120h, cyclic oxidation (thermal shocks) at 1150°C and finally hot corrosion test at 1000°C. Microstructural characterization of coatings was also performed using SEM, FESEM, XRD and EDX. The results showed that both TGO growth and CSNs were considerably reduced with the use of nano NiCrAlY/YSZ/nano Al2O3 coating compared to the other coatings. It was found that pre-oxidation treatment and particularly TBC system microstructure can influence the evolution of TGO layer and TBCs durability during service at elevated temperatures.