CMAS Corrosion Behavior and Its Mechanism of Plasma-sprayed 56YSZ Coatings at 1 350 ℃

HU Yanhao; FAN Xizhi; HUANG Wenzhi; ZHAO Kairui; MAO Weiguo

doi:10.16490/j.cnki.issn.1001-3660.2025.12.005

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Surface Technology ›› 2025, Vol. 54 ›› Issue (12) : 61-71. DOI: 10.16490/j.cnki.issn.1001-3660.2025.12.005

Corrosion and Protection

CMAS Corrosion Behavior and Its Mechanism of Plasma-sprayed 56YSZ Coatings at 1 350 ℃

HU Yanhao^1,2, FAN Xizhi¹, HUANG Wenzhi^2,*, ZHAO Kairui^2,3, MAO Weiguo^1,*

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Abstract

The CMAS (calcium-magnesium-alumino-silicate) corrosion behavior of the free-standing 56 wt.% yttria stabilized zirconia (56YSZ) coatings fabricated via atmospheric plasma spraying process at 1 350 ℃ is investigated and its corrosion mechanism is also elucidated in the research. Firstly, the mixture powders composed of 33% CaO, 9% MgO, 13% AlO_1.5, and 45% SiO₂ are uniformly mixed and coated to the surface of as-deposited coatings, and then the coated samples are subject to high-temperature exposure in a muffle furnace at 1 350 ℃ for different times. After corrosion at 1 350 ℃ for different times, the phase composition and microstructure of the corrosion products are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectroscopy (EDS). As a result, the corrosion depth of 56YSZ coating is increased rapidly from (57.6±6.7) μm to (150.9±11.0) μm with the prolonged exposure time after being exposed at 1 350 ℃, and the final corroded layer with the thickness of (172.5±18.3) μm is achieved after corrosion for 50 h. It is easy to note that a positive relationship between the depth of the corroded layer and the corrosion duration is obtained. During the initial stage of corrosion, the CMAS mixture powders are deposited on the coating surface and gradually melted with the increasing temperature, which could be infiltrated into the coating through the presence of cracks and pores. As we all know, the CMAS corrosion rate is directly related to the viscosity of the melt and its element content. In this corrosion stage, the CMAS melt would quickly react with Y³⁺ to form an apatite phase, and the corrosion rate is also increased, which is mainly attributed to the richest CMAS melt and its highest viscosity. However, the viscosity of the CMAS melt is then reduced under the combined effect of the decreasing SiO₂/CaO ratio and the permeate of Y³⁺. With the reaction proceeding, the apatite phase consumes large amounts of Si⁴⁺ and Ca²⁺, and lower Si⁴⁺/Al³⁺ ratio in the CMAS melt creates favorable conditions for the formation of garnet, resulting in the decrease of the corrosion rate from 28.8 μm/h to 15.9 μm/h. After corrosion for 4 hours, it is observed that the two dense layers appear in the inner region and the outer region of the corrosion layer. Based on the element distribution, the outer region of the corrosion layer is mainly consisted of c-ZrO₂ and the apatite phase, while the c-ZrO₂ and the garnet phase present in the inner region. Due to the formation of dense layers, the CMAS melt penetration is blocked. When the corrosion time is prolonged to 8 hours, the elements in the melt are nearly consumed and the corrosion rate is significantly reduced to 0.5 μm/h. At this stage of corrosion reaction, the appearance of element diffusion and segregation is present in the corrosion products, and large-scale pores appear in the corrosion layer, while a thin calcium-rich layer is formed on the surface. Consequently, the CMAS corrosion behavior of plasma-sprayed 56YSZ coating could be divided into three stages, including the initial rapid corrosion dominated by the thermal penetration of CMAS melt, followed by the formation of a dense layer composed of apatite and garnet phases via thermochemical reactions, and the arreargae of the CMAS corrosion resulting in the slowly increase of corrosion layer. The primary phases in the CMAS corrosion products are found to be c-ZrO₂, apatite, and garnet. It is concluded that the 56YSZ coating could be considered to be a promising candidate material for thermal barrier coatings (TBCs) with exceptional CMAS corrosion resistance.

Key words

high yttria stabilized zirconia / CMAS corrosion / thermal barrier coating / corrosion mechanism / thermal penetration / atmospheric plasma spraying

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HU Yanhao, FAN Xizhi, HUANG Wenzhi, ZHAO Kairui, MAO Weiguo. CMAS Corrosion Behavior and Its Mechanism of Plasma-sprayed 56YSZ Coatings at 1 350 ℃[J]. Surface Technology. 2025, 54(12): 61-71 https://doi.org/10.16490/j.cnki.issn.1001-3660.2025.12.005

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