Materials scientists have long sought to enhance the durability of TBCs used in advanced aero-engines, where service conditions inevitably introduce volcanic ash, dust, and sand particles into the combustion chamber. Once ingested, these silicate particles melt into calcium–magnesium–alumina–silicate (CMAS) glass that readily wets and penetrates conventional yttria-stabilized zirconia (YSZ) coatings, triggering chemical reactions, pore infiltration, and ultimately TBCs cracking or spallation. Although YSZ remains the most widely applied TBC material, its almost negligible resistance to CMAS corrosion falls short of the thermal stability required for next-generation high-efficiency gas turbines.
Recently, a team of material scientists led by Lei Guo from Tianjin University, China, first reported a bilayer-structured apatite layer, detailing its preparation process, high-temperature structural and phase stability, thermal cycling performance, as well as its CMAS wetting behavior and infiltration resistance. This work not only explains the preparation mechanism and anti-CMAS wetting mechanism of the bilayer-structured apatite layer, but also predicts that the bilayer-structured apatite layer can be used as a highly promising CMAS protective layer for TBCs.
The team published their work in Journal of Advanced Ceramic s on September 12, 2025.
"In this study, a bilayer-structured apatite layer was constructed by pre-reacting GdPO4 with CMAS powders, which consisted of an acicular upper layer and a compact lower layer. The bilayer-structured apatite layer has been found to play a decisive role in enhancing the CMAS corrosion resistance of TBCs. Therefore, we propose that it can serve as a protective layer for TBCs. However, its preparation conditions, high-temperature stability, and CMAS wetting resistance have not been reported," said Lei Guo, professor at the School of Materials Science and Engineering, Tianjin University (China), an expert whose research interests focus on the field of CMAS protection for TBCs.
"Ideally, the bilayer-structured apatite layer should feature a continuous compact lower layer, and the acicular crystals in the upper layer grow in an ordered manner perpendicular to the substrate surface. To obtain such an ideal bilayer structure, we continuously adjusted the pre-reaction conditions and found that temperature and time significantly influence the formation rate and growth orientation of the apatite crystals, and CMAS concentration primarily determines the thickness and continuity of the reaction layer. Notably, covering the GdPO4 surface with 5 mg/cm2 of CMAS powder and heat treating at 1250 °C for 1 h enabled the construction of the most ideal bilayer-structured apatite layer," said Lei Guo.
The bilayer-structured apatite layer exhibits low wettability to molten CMAS, excellent structural integrity after 50 h heat treatment at 1250 °C and 100 thermal cycles, and strong resistance to CMAS infiltration even after CMAS exposure for 20 h. The CMAS contact angle on the bilayer-structured apatite layer reached 17.4° at 1250 °C for 30 min, exhibiting excellent low-wettability to CMAS. "From the perspective of resisting molten CMAS, the bilayer-structured apatite layer represents an eligible protective layer for TBCs," said Lei Guo.
However, more delicate research works are still needed to explore the suitability of the bilayer-structured apatite layer as a novel protective layer for TBCs. In this regard, future work will focus on directly applying this bilayer-structured apatite protective layer onto TBCs to reduce molten CMAS wettability and adhesion, aiming to fundamentally address the CMAS issue of TBCs.
Other contributors include Lanxin Zou, Shijun Meng from the School of Materials Science and Engineering at Tianjin University in Tianjin, China; Yuxian Cheng from the AECC Shenyang Liming Aero Engine Co., Ltd. in Shenyang, China.
This work was sponsored by the Innovation Project (D925BCD), the National Natural Science Foundation of China (Grant Nos. 52471087 and 52272070), and the National Science and Technology Major Project (J2022-Ⅵ-0009-0040).
About Author
Lei Guo is an Associate Professor and Ph.D. supervisor at the School of Materials Science and Engineering, Tianjin University, China, and Deputy Director of the Institute of Welding and Advanced Manufacturing Technology. His research focuses on high-temperature protective coatings for aero-engines, hydrogen-resistant coatings and welding metallurgy. He has received the First Prize of Science and Technology Award from the Chinese Society for Corrosion and Protection (ranked 1st). He has published over 80 SCI papers as first or corresponding author, including in J. Adv. Ceram., Corros. Sci., and J. Eur. Ceram. Soc., with 8 papers having impact factors above 15, cited over 3000 times (H-index 40), and holds 4 authorized Chinese invention patents. He has also led multiple national-level projects, including three NSFC grants (general and youth).
About Journal of Advanced Ceramics
Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen . JAC's 2024 IF is 16.6, ranking in Top 1 (1/33, Q1) among all journals in "Materials Science, Ceramics" category, and its 2024 CiteScore is 25.9 (5/130) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508
