Formation of a dense and continuous Al2O3 layer in nano thermal barrier coating systems for the suppression of spinel growth on the Al2O3 oxide scale during oxidation

•Formation of a dense and continues Al2O3 (TGO) layer on the nanostructured NiCrAlY.•Formation of a discontinues and thicker Al2O3 (TGO) layer on the normal NiCrAlY.•Bi-layered TGO thickness in normal TBC system was much higher.•Continues and thin Al2O3 layer on the nano BC would act as an infiltration barrier.•Bi-layered TGO thickness can predict TBC durability during cyclic oxidation.

A continuous and thin Al2O3 layer would act as an infiltration barrier to diminish the growth of spinels in thermal barrier coating systems. Therefore, isothermal oxidation of normal NiCrAlY/YSZ, nano NiCrAlY/YSZ and nano NiCrAlY/YSZ/nano Al2O3 coatings was investigated at 1000 °C. These samples were then subjected to thermal cycles at 1150 °C. The microstructural characterisation showed that the spinel growth in the nano NiCrAlY/YSZ/nano Al2O3 coating was much lower than the other coatings. This observation can be related to the formation of a fully continuous Al2O3 layer on the nano NiCrAlY coating during pre-oxidation at 1000 °C and also to the presence of a nano Al2O3 layer over the YSZ coating.