Weiguo Mao

As turbine inlet temperatures in advanced aeroengines and heavy-duty gas turbines continue to rise, conventional thermal and environmental barrier coatings (TBCs/EBCs) are increasingly confronted with critical operational bottlenecks. They are increasingly plagued by deleterious high-temperature phase transformations, thermal expansion mismatch with substrates, and catastrophic degradation induced by molten calcium–magnesium–aluminosilicate (CMAS) and water vapor corrosion. To decisively break these inherent limitations, high-entropy rare-earth oxides (HEREOs) have rapidly emerged as a revolutionary materials paradigm. Driven by configurational entropy stabilization, severe lattice distortion, and sluggish diffusion effects, HEREOs uniquely synchronize ultralow thermal conductivity, tailorable thermal expansion coefficients, and exceptional chemical inertness within a single crystal lattice. This comprehensive review systematically navigates the cutting-edge advancements of HEREOs for next-generation hot-section protection. It first demystifies the intricate process–microstructure relationships during coating deposition, highlighting the nonequilibrium phase evolution induced by thermal spraying. Subsequently, it critically dissects high-temperature phase stability, multiscale defect-engineered thermophysical properties, and intricate failure mechanisms under CMAS and water vapor attack. Notably, to counteract the intrinsic brittleness and improve the inferior fracture toughness of HEREOs, advanced structural engineering—incorporating multiphase synergistic toughening and gradient architectures—is highlighted as a crucial strategy for enhancing thermal shock durability. Finally, transitioning from empirical trial-and-error to a predictive framework, this review envisions a machine-learning-empowered inverse design paradigm, offering a data-driven roadmap for multiobjective optimization and lifetime prediction of highly robust HEREO coatings. This contribution also statistically outlines the latest research trends, offering researchers forward-looking guidance and evidence-based references.

Four kinds of sugar (glucose, fructose, sucrose, and maltose) were selected as carbon precursors, and corresponding dense carbon products were prepared using a novel hydrogel carbonization method. The carbonization processes of sugar–polyacrylamide (sugar–PAM) hydrogels were studied in detail. The molecular structures in the raw materials were analyzed by proton nuclear magnetic resonance spectroscopy (¹H NMR). Samples prepared at different temperatures were characterized by thermogravimetry analysis (TGA) and Fourier-transform infrared (FTIR) spectroscopy. The morphology and microstructure of sugar-derived carbons were confirmed by field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The results indicated that the sugar solution was surrounded by PAM with a three-dimensional network structure and formed hydrogels in the initial stage. The sugar solution was considered to be separated into nanocapsules. In each nanocapsule, sugar molecules could be limited within the hydrogel via walls formed by PAM chains. The hydroxyl group in the sugar molecules connected with PAM by the hydrogen bond and intermolecular force, which can strengthen the entire hydrogel system. The self-generated pressure of hydrogel constrains the foam of sugar during the heat treatment. Finally, dense carbon materials with low graphitization instead of porous structure were prepared at 1200 °C.

Wear-resistant Cu-Zr-Al-Ag-Co amorphous coatings were fabricated by high-velocity air-fuel spray technology using (Cu₄₃Zr₄₇Al₇Ag₃)_99.5Co_0.5 powder at different temperatures (i.e., 645, 725, and 805 K). The feedstock powders (98.6 wt.% amorphous phase) were produced by a gas atomization method. Thermal properties and microstructure of the powders and the coatings were comparably investigated by differential scanning calorimeter, scanning electron microscope, and transmission electron microscopy techniques. Wear properties were studied by a dry sliding wear tester under the linear reciprocating sliding in a ball-on-plate mode using a GCr15 ball as the counterpart at room temperature in air. A large fraction of amorphous phase (~67.5 wt.%) and crystalline phases (ZrO₂, Al_2.5Cu_0.5Zr, and AlZr₃) are found in the coating fabricated at a temperature (725 K) between the glass transition temperature (T_g) and the onset crystallization temperature (T_x). In addition, the coating also exhibits the highest Vickers hardness (554 HV_0.1), bonding strength (59.3 MPa), a relatively low porosity (1.65%), and superior wear resistance. The wear mechanism of the coating is primarily abrasive wear and slight adhesive wear.

The lithiation induced stress in multilayer silicon/graphite-based electrodes for lithium ion batteries is evaluated analytically. Firstly, the silicon/graphite-based composite active layer is reinforced by Ti₃C₂ MXene, and the effects of Ti₃C₂ MXene additive on elastic modulus of the active layer are discussed based on the Halpin–Tsai empirical equation. Secondly, biaxial stresses in both bilayer and symmetric trilayer silicon/graphite-based electrodes are estimated by a mechano-electrochemical model, which is derived by imitating thermal expansion stress in layered structural components. And the effects of Ti₃C₂ MXene’s parameters, including additive amount, number of layers and length–width ratio, on the stress in multilayer silicon/graphite-based electrodes are also be discussed in detail. Finally, based on the numerical analysis, some design strategies for Ti₃C₂ MXene reinforced composite active layer are proposed from mechanical views.