In situ observation of environmental barrier coating against calcium–magnesium–alumina–silicate attack at elevated temperature

Abstract

The service conditions of the hot-end components of aeroengines are extremely harsh. 1 In addition to the complex load and water vapor environment, the materials are suffered damage from sand and dust, which are ingested into the engine by the intake air. 2 Silicon carbide fiber-reinforced silicon carbide matrix composites (SiC f /SiC) are considered to be one of the most promising thermal structural materials in the next generation of aero-engines due to their low density and excellent thermomechanical properties at high temperatures. [3][4][5] Coating an environmental barrier coating (EBC) on their surface can further improve the high temperature oxidation resistance of the SiC f /SiC composite. [6][7][8] Generally, EBC is mainly composed of two parts with different functions. One layer made of rare earth silicates (such as Yb 2 SiO 5 , La 2 SiO 5 ) exposing to the environment acts as a thermal blocker of high heat flow at high temperature and an isolator for water-oxygen and corrosion gas; the other layer composed of Si acts as the bonding layer to relief the mismatch in coefficient of thermal expansion (CTE) between the composites and the outer coatings. [9][10][11][12] The main components of the ingested particles in the engines are calcium-magnesium-alumina-silicon (CMAS).

Water vapor and CMAS corrosion tests of Y2SiO5/Si thermal and environmental barrier coating

“…At 1300 C, the reaction speed began to accelerate. The thickness of the reaction layer at different reaction times was consistent with previous studies, indicating the validity of the data [26][27][28][29][30].…”

“…It can be summarized from the variation of the elemental proportions shown in Figure 7 that Ca and Si in CMAS continuously permeate into Y 2 SiO 5, leading to the formation of a reaction zone between melted CMAS and Y 2 SiO 5 . This reaction zone can effectively stop the mutual diffusion of elements in CMAS and Y 2 SiO 5 [ 27 , 28 , 29 ]. Therefore, Y is not capable of diffusing into the reaction zone and the CMAS layer, and Mg and Al are only detected in the CMAS layer.…”

“…The amount of Si also decreases to a certain degree in the Y 2 SiO 5 layer.It can be summarized from the variation of the elemental proportions shown in Figure7that Ca and Si in CMAS continuously permeate into Y 2 SiO 5, leading to the formation of a reaction zone between melted CMAS and Y 2 SiO 5 . This reaction zone can effectively stop the mutual diffusion of elements in CMAS and Y 2 SiO 5[27,28,29]. Therefore, Y is not capable of diffusing into the reaction zone and the CMAS layer, and Mg and Al are only detected in the CMAS layer.Figure8displays the phase composition of the mixture of Y 2 SiO 5 and CMAS powders at a weight ratio of 1:1 after heating at 1300 C for 30 min and 4 h, respectively.…”

Design of Ti 2AlC/YSZ TBCs for more efficient in resisting CMAS attack

“…However, when aircraft flies across volcanoes, deserts, and other areas, environmental particles such as sand and dust, whose main component is calciummagnesium-alumina-silicate (CMAS), would be ingested into the engine and deposited on blade surfaces [5]. At high temperatures, CMAS melts, penetrates, and blocks coating micropores, reducing strain tolerance.…”