It is of great significance to search oxide thermal/environmental barrier coatings (T/EBCs) with high working temperatures and thermal expansion coefficients (TECs) matching to different substrates. ABO4-type oxides have been widely studied due to their high working temperatures, adjustable TECs, and low thermal conductivity. In this work, ABO4-type (A=Ga, In, Cr; B=Nb, Ta) oxides are studied as EBC candidates based on their relatively low TECs. The influences of crystal structures, distortion degree, types of polyhedrons, as well as the A- and B-site ionic radii and atomic weights on TECs are discussed. It is found out that the TECs of ABO4-type oxides are not depended on one single factor, and reducing A-site ionic radius may be a good way to decrease their TECs. Based on the TECs, AlNbO4, InNbO4, and GaTaO4 are chosen as EBCs for C-, SiC-, and Al2O3-based substrates, respectively. The similar TECs between ABO4-type oxide EBCs and substrates are beneficial for reducing interfacial thermal stress, which is good for their long-term applications. This work shows that the applications of ABO4-type oxides can be expanded by effectively regulating TECs.
Thermal and environmental barrier coatings play a crucial role in protecting high-temperature structural components in gas turbine engines. As turbine inlet temperatures continue to rise, corrosion challenges posed by dust, volcanic ash, and other particulate matter—collectively known as CMAS—have become increasingly severe. Understanding the reaction mechanisms between CMAS and these coatings, identifying the key factors influencing CMAS corrosion, and developing methods to inhibit CMAS infiltration are essential for advancing high-performance gas turbine engines. This review examines the origins of CMAS corrosion and summarizes recent research on CMAS corrosion mechanisms in thermal and environmental barrier coating materials. Additionally, the role of rare earth elements in CMAS corrosion and various strategies to mitigate CMAS effects are discussed. Finally, the review highlights potential directions for future research.
With the advancement of hypersonic vehicles, extreme high temperature environments have imposed increasingly stringent requirements on the performance of thermal protection systems. Consequently, the development of high-performance thermal protection materials capable of withstanding extreme conditions has become a primary focus of current research. Ultra-high temperature ceramics (UHTCs) and their composites, known for their excellent oxidation resistance and ablation performance, are regarded as highly promising non-ablative thermal protection materials. This paper provides a systematic review of recent research progress on UHTC composites in several key areas, including innovations and optimizations in fabrication processes, exploration of toughening strategies and mechanisms, in-depth studies on oxidation and ablation resistance mechanisms, and the development and potential applications of high-entropy ceramics. Furthermore, the paper discusses the practical application prospects of UHTCs and their composites in extreme environments, analyzes the current technical challenges, and proposes future research directions and priorities.
