Microstructural analysis and thermal shock behavior of plasma sprayed ceria-stabilized zirconia thermal barrier coatings with micro and nano Al2O3 as a third layer

• The presence of a dense alumina layer over the usual TBC significantly improved the durability of the TBCs.
• Nano alumina top layer has a lowest amount of gamma alumina in the as-sprayed coating.
• The coating made with the nano-alumina powder has a higher thermal shock resistance.

In this study, thermal shock behavior of three types of atmospheric plasma sprayed ceria-stabilized zirconia (CSZ) thermal barrier coatings was evaluated: usual CSZ, layer composite of CSZ/Micro Al2O3 and layer composite of CSZ/Nano Al2O3 in which Al2O3 was used as a top coat on CSZ layer. The thermal shock test was administrated by quenching the samples in the cold water with the temperature of 20–30 °C from 1100 °C. Microstructure evaluation, elemental and phase analysis of coatings before and after tests were performed using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry, respectively. The experimental results revealed that the CSZ/Nano Al2O3 TBC has a superior thermal cycling behavior, in comparison to CSZ/Micro Al2O3 and usual CSZ TBCs. Also, failures of both usual CSZ and layer composite of CSZ/Micro Al2O3 TBCs mainly were associated with thermally grown oxide formation and growth stresses at NiCrAlY/CSZ interface, whereas, in CSZ/Nano Al2O3 TBC, the failure mechanism was coefficient of thermal expansion mismatch stress in NiCrAlY/CSZ interface.