Corrosion Behavior and Mechanism of Aluminum-rich CMAS on Rare-earth Silicate Environmental Barrier Coatings:

Abstract

Environmental barrier coatings (EBCs) are expected to be applied to the hot-section components of a new generation of high thrust-to-weight ratio aero-engines. Rare-earth silicates have been acknowledged as promising alternatives to EBC materials due to their superior high-temperature phase stability, suitable coefficient of thermal expansion and long durability in water vapor. However, the calcium-magnesium-alumino-silicates (CMAS) molten salt corrosion under service conditions have become a bottleneck that limits the application of EBCs. Factors such as the composition of CMAS and the crystal structures of rare-earth silicates have a significant impact on their corrosion behavior. In this paper, X1-Gd2SiO5 and X2-RE2SiO5 (RE=Y, Er) coatings with different crystal structures, were prepared by atmospheric plasma spraying (APS) technique. The corrosion behaviors and mechanisms of the three kinds of coatings under molten CMAS melt environment at 1400 ℃ were explored. Results showed that the corrosion resistance of X2-RE2SiO5 coatings were better than that of the X1-Gd2SiO5 coating due to their phase compositions and stability of crystal structure. After corrosion by CMAS, the X1-Gd2SiO5 coating dissolved in CMAS melt and formed apatite phase, while the X2-RE2SiO5 coatings not only formed apatite phase, but also formed garnet phase from reaction of the RE2O3 in

Mechanical and thermal properties for corrosion products of lutetium silicates against CMAS

“…1,2 Rare-earth (RE) silicates are considered as promising novel E/TBC candidates, which exhibit excellent mechanical properties and thermal properties, such as low modulus, good damage tolerance, low thermal conductivity, coefficient of thermal expansion (CTE), and so on. [3][4][5][6][7] Among all silicates, lutetium silicates are widely studied owing to their excellent CMAS corrosion resistance and similar CTE values with SiC and mullite. 8 Tian et al observed that Lu 2 SiO 5 has excellent hightemperature durability and low thermal conductivity (1.72 W ⋅ m −1 ⋅ K −1 at 1273 K).…”

“…Previous studies mainly focused on the intrinsic properties of precorrosion coatings and their micromorphology in postservice stage. 5,11,13 Actually, a lot of experimental works reported that the products came to being from the reaction between RE silicates and CMAS with the progress of corrosion. A fine apatite phase layer was observed on the surface of 𝛾-Y 2 Si 2 O 7 under CMAS corrosion, and anorthite, pseudowollastonite, apatite, and so on, also were detected between the RE 2 Si 2 O 7 (RE = Yb, Lu, La, Gd, Eu, Sc, and Y) and CMAS.…”

“…Environmental/thermal barrier coatings (E/TBCs) are used to protect silicon‐based ceramic matrix composites (CMCs) substrates in aerospace engines from oxidation and corrosion, prolonging the service life of engine components 1,2 . Rare‐earth ( RE ) silicates are considered as promising novel E/TBC candidates, which exhibit excellent mechanical properties and thermal properties, such as low modulus, good damage tolerance, low thermal conductivity, coefficient of thermal expansion (CTE), and so on 3–7 . Among all silicates, lutetium silicates are widely studied owing to their excellent CMAS corrosion resistance and similar CTE values with SiC and mullite 8 .…”

“…RE silicate E/TBCs will be corroded by CaO‐MgO‐Al 2 O 3 ‐SiO 2 (CMAS) in a sand or volcanic ash environment, which could lead to E/TBC surface recession and spallation. Previous studies mainly focused on the intrinsic properties of precorrosion coatings and their micromorphology in postservice stage 5,11,13 . Actually, a lot of experimental works reported that the products came to being from the reaction between RE silicates and CMAS with the progress of corrosion.…”

Effect of calcium–magnesium–aluminum silicate composition on reaction behavior for X1‐Gd2SiO5 and X2‐Er2SiO5 environmental barrier coatings

“…28 Many of the modeled CMAS compositions in previous studies were based on engine sediments, which are quite different from the natural mineral sources of CMAS. [29][30][31][32] Stokes et al investigated the effect of different CMAS (Ca/Si ratio = 0.635, 0.478, and 0.096) on the corrosion behaviors for RE 2 Si 2 O 7 (RE = Er, Dy, Gd, and Nd) bulk materials, and showed that an increase in the CaO content resulted in the generation of apatite phases during the corrosion process. 33 Summers et al investigated the corrosion behaviors of Y 2 Si 2 O 7 blocks against CMAS with different compositions at 1300 • C and 1400 • C, respectively.…”