Abstract
In this study, yttria-stabilized zirconia (YSZ) coatings were deposited by atmospheric plasma spraying (APS) using feedstocks with two different particle sizes. The effect of particle size on the pore structure and failure mechanism of the coatings was investigated. The evolution of the pore structure of the two kinds of coatings during cyclic thermal shock test was described by quantitative metallography. The influence of pore orientation on the thermal stress of the coating system was analyzed by the finite element method. It was found that the coatings deposited using coarse particles show a high thermal shock life time. The orientation of the pores in the coatings prepared by different particle sizes was different. A structural parameter was proposed to effectively characterize the pore orientation of the coatings. Coatings prepared by coarse YSZ powder tend to form almost the same number of horizontal and vertical pores, while coatings prepared by fine powder tend to form horizontal ones parallel to the direction of the substrate. The simulation results revealed that the vertical pores can reduce the thermal stress in the coating. The results of this investigation are a benefit to the design and integrity of TBCs.
Highlights
The thermal barrier coatings (TBCs) are widely used in hot sections of gas-turbine engines to improve their operating temperature and provide thermal protection for the underlying metallic components, thereby improving the efficiency and performance of the engine [1,2]
The TBC systems generally consist of four layers which are the substrate, the bond coat (BC), the thermally-grown oxide (TGO), and the ceramic top coat (TC) [1]
Due to the thermal expansion coefficient difference between the ceramic coating and the metallic material, thermal mismatch stress appears in the coating system under cyclic thermal shock conditions, resulting in the cracking and peeling of the ceramic layer [3,4]
Summary
The thermal barrier coatings (TBCs) are widely used in hot sections of gas-turbine engines to improve their operating temperature and provide thermal protection for the underlying metallic components, thereby improving the efficiency and performance of the engine [1,2]. The TBC systems generally consist of four layers which are the substrate, the bond coat (BC), the thermally-grown oxide (TGO), and the ceramic top coat (TC) [1]. Due to the thermal expansion coefficient difference between the ceramic coating and the metallic material, thermal mismatch stress appears in the coating system under cyclic thermal shock conditions, resulting in the cracking and peeling of the ceramic layer [3,4]. Plasma-sprayed TBCs are widely used due to their low production cost and versatility. In this method, YSZ powders are carried by an inert gas mixture into the plasma plume where they are melted, accelerated, and propelled against a substrate. The molten particles impact and solidify on the substrate creating the characteristic lamellar microstructure with a typical porosity of 10%–20% [5,6]
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