Isothermal Oxidation Behavior of Gd₂Zr₂O₇/YSZ Multilayered Thermal Barrier Coatings

Abstract

Efficiency of a gas turbine can be increased by increasing the operating temperature. Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used in gas turbine applications. However, above 1200°C, YSZ undergoes significant sintering and CMAS (calcium magnesium alumino silicate) infiltration. New ceramic materials of rare earth zirconate composition such as gadolinium zirconate (GZ) are promising candidates for thermal barrier coating applications (TBC) above 1200°C. Suspension plasma spray of single-layer YSZ, double-layer GZ/YSZ, and a triple-layer TBC comprising denser GZ on top of GZ/YSZ TBC was attempted. The overall coating thickness in all three TBCs was kept the same. Isothermal oxidation performance of the three TBCs along with bare substrate and bond-coated substrate was investigated for time intervals of 10 h, 50 h, and 100 h at 1150°C in air environment. Weight gain/loss analysis was carried out by sensitive weighing balance. Microstructural analysis was carried out using scanning electron microscopy (SEM). As-sprayed single-layer YSZ and double-layer GZ/YSZ showed columnar microstructure, whereas the denser layer in the triple-layer TBC was not columnar. Phase analysis of the top surface of as-sprayed TBCs was carried out using XRD. Porosity measurements were made by water intrusion method. In the weight gain analysis and SEM analysis, multilayered TBCs showed lower weight gain and lower TGO thickness compared to single-layer YSZ.

Improved hot corrosion resistance of plasma sprayed YSZ/Gd2Zr2O7 thermal barrier coating over single layer YSZ

“…In the present conditions, the molten corrosive salts available have completely reacted with GZO layer forming GdVO 4 as corrosive products thereby preventing the underlying YSZ from damage. Also, the presence of unreacted Na 2 SO 4 on the surface of the coating and as confirmed by EDS analysis could be due to the fact that the melting point and boiling point of Na 2 SO 4 is 884 °C and 1404 °C respectively, some of the molten sodium sulphate may evaporate after higher temperature thermal exposure > 1000 °C [29,30]. Whereas, from the crosssectional images of YSZ/GZO TBCs after 30 h of hot corrosion treatment, it is noticeable that the interfaces are very much intact with good adhesion.…”

“…12(a). This well-known phenomenon is due to the transformation of high density metallic bond coat to low density oxide with low coefficient of thermal expansion by the addition of oxygen within the coating volume [29]. The cross-section micrographs of YSZ/ GZO TBCs after thermal cycling test in Fig.…”

Durability of Gadolinium Zirconate/YSZ Double-Layered Thermal Barrier Coatings under Different Thermal Cyclic Test Conditions

“…In a TBC, the bond coated surface could be accessed (oxidized) by oxygen via two possible routes i.e., from the open porosity through TBC and the oxygen ion vacancies in the crystal structure of the ceramic. It is speculated that the oxygen penetration resistance of rare earth zirconate based pyrochlores is higher than YSZ due to their cubic crystal structure having a systematic arrangement of the oxygen ion vacancies [28,29]. Moreover, the porosity content in the GZ layer has also been shown to be lower than that in the YSZ layer, thereby further contributing to the better oxygen penetration resistance.…”

Suspension High‐Velocity Oxy‐Fuel–Sprayed Dense Vertically Cracked and Suspension‐Plasma‐Sprayed Columnar Yttria‐Stabilized Zirconia Coatings: Calcia Magnesia Alumino Silicates Infiltration and Thermal Cycling Performance

“…This might alter the heat transfer and subsequently the formation of the final deposition. [ 36,37 ] It was imperative to mention that the injection of nitrogen as the carrier or atomizing gas was expected to improve the in‐flight particle temperatures by enhancing the overall flame efficiency. The suspension was injected using a 0.02 in (0.51 mm) diameter injector and a 3/8 in (9.52 mm) exit nozzle was used for the torch.…”