A novel CMAS‐resistant material based on thermodynamic equilibrium design: Apatite‐type Gd₁₀(SiO₄)₆O₃

Abstract

Calcium‐magnesium‐alumino‐silicates (CMAS) melt attack has been a critical issue for the thermal barrier coatings (TBCs) with ever‐increasing engine operating temperature. In this study, a novel CMAS‐resistant material apatite‐type Gd10(SiO4)6O3 is developed for TBCs application based on thermodynamic equilibrium design. The chemical reaction of Gd10(SiO4)6O3 bulk and CMAS melt is investigated at 1300°C. The CMAS corrosion resistance of Gd10(SiO4)6O3 bulk is evaluated and compared with the well‐studied CMAS‐resistant material Gd2Zr2O7 (GZO). It is found that Gd10(SiO4)6O3 shows a significantly enhanced CMAS resistance, including lower intrinsic CMAS infiltration rate (~1.09 μm/h1/2) and smaller infiltration upper limit (50‐62 μm) for a 20 mg/cm2 CMAS deposition. More importantly, for Gd10(SiO4)6O3, the CMAS infiltration only alters the composition but does not change the crystal structure or destroy microstructural integrity. The reaction mechanism is elucidated as following two stages: (a) surface Gd10(SiO4)6O3 quickly transforms into Ca2Gd8(SiO4)6O2 in suit by interdiffusion with CMAS melt and then is thermodynamically stable with CMAS melt, thereby effectively inhibiting the further CMAS infiltration and (b) with the ongoing interdiffusion of Gd/Ca, the CMAS‐infiltrated layer slowly thickens and follows a parabolic law. Meanwhile, the CMAS melt gradually precipitates Ca2Gd8(SiO4)6O2 and CaAl2Si2O8 (anorthite) until the melt is exhausted.

Experimental and Simulation Analysis of the Evolution of Residual Stress Due to Expansion via CMAS Infiltration in Thermal Barrier Coatings

“…where T h denotes the holding time (h). Note that the depth R(T h ) of the CMAS-rich layer follows the parabolic law by Wu et al [25]. This study [24] also indicated that the infiltration behavior is initially faster and becomes slower as the holding time still operates.…”

Revolutionary High-entropy Zr-Y-Yb-Ta-Nb-O Oxides for Next Generation Thermal Barrier Coating Applications

“…As t-4 presents the lowest thermal conductivity, highest CTE and exceptional hightemperature stability, its resistance against CMAS corrosion is evaluated and compared with those of the state-of-the-art YSZ and the excellent CMAS-resistant material Gd2Zr2O7 [29], as shown in Fig. 2e.…”

ZrO2‐doped YTaO4 as potential CMAS‐resistant materials for thermal barrier coatings application

“…The low-magnification cross-sectional SEM images of CMAS reacted Zr x Y 0.5−x/2 Ta 0.5−x/2 O 2 (x = 0, 0.1, 0.2, 0.28) bulks are presented in Figure 3. The CMAS infiltration depth were measured from the initial surface (red dash line) to CMAS infiltration front (black dash line), based 20 As shows in Figure 2B-E, the as-sintered ZrO 2doped YTaO 4 bulks have a notable difference in the grain size, which may influence the CMAS infiltration depth. Generally, the smaller the grain size, the higher grain boundary density, which may cause the higher corrosion rate.…”

“…For Gd 2 Zr 2 O 7 , the dense reaction layer can rapidly form, but cannot thicken over reaction time, therefore it shows a linearly CMAS infiltration rate, which has been elucidated in our previous work. 20 Figure 8A-D presents the high-magnification BSE images of the surface region of the reaction layer in Zr x Y 0.5−x/2 Ta 0.5−x/2 O 2 (x = 0, 0.1, 0.2, 0.28) after 50 h corrosion. It is found that the grain size of CRP initially increases and then decreases with increasing ZrO 2 doping content in bulk materials.…”

“…calcium-magnesium-alumino-silicates (CMAS), corrosion, thermal barrier coatings (TBCs), YTaO 4 , ZrO 2 However, it was found that RE zirconates, e.g., Gd 2 Zr 2 O 7 , have limited resistance for long-term CMAS corrosion because the formed dense reaction layer cannot thicken over the reaction time. 20 Note that the long-term CMAS resistance is very important with the consideration of long lifetime requirement of TBCs (e.g. several thousand hours).…”