Thermal behaviour of multilayer and functionally-graded YSZ/Gd2Zr2O7 coatings

Abstract

[EN] Zirconates with pyrochlore structure, such as Gd2Zr2O7, are new promising thermal barrier coatings because of their very low thermal conductivity and good chemical resistance against molten salts. However, their coefficient of thermal expansion is low, therefore their thermal fatigue resistance is compromised. As a solution, the combination of yttria-stabilised zirconia (YSZ) and Gd2Zr2O7 can reduce the thermal contraction mismatch between the thermal barrier coating parts. In the present study, two possible designs have been performed to combine YSZ/Gd2Zr2O7. On the one hand, a multilayer coating was obtained where YSZ layer was deposited between a Gd2Zr2O7 layer and a bond coat. On the other hand, a functionally-graded coating was designed where different layers with variable ratios of YSZ/Gd2Zr2O7 were deposited such that the composition gradually changed along the coating thickness. Multilayer and functionally-graded coatings underwent isothermal and thermally-cycled treatments in order to evaluate the oxidation, sintering effects and thermal fatigue resistance of the coatings. The YSZ/Gd2Zr2O7 multilayer coating displayed better thermal behaviour than the Gd2Zr2O7 monolayer coating but quite less thermal fatigue resistance compared to the conventional YSZ coating. However, the functionally-graded coating displays a good thermal fatigue resistance. Hence, it can be concluded that this kind of design is ideal to optimise the behaviour of thermal barrier coatings. ; This work has been supported by the Spanish Ministry of Economy and Competitiveness (project MAT2015-67586-C3-R). A. Borrell acknowledges the Spanish Ministry of Economy and Competitiveness for her Juan de la Cierva-Incorporacion contract (IJCI-2014-49839) and the Program to Support Research and Development (PAID-00-15) of the Universitat Politecnica de Valencia. P. Carpio acknowledges the Valencia Government for his post-doc contract (APOSTD/2016/040). ; Carpio-Cobo, P.; Salvador Moya, MD.; Borrell Tomás, MA.; Sanchez, E. (2017). Thermal ...