Aluminum oxide (Al₂O₃), as a high-performance structural ceramic material with high melting point, high toughness, good chemical stability, and excellent wear resistance, is one of the best candidate materials for high-temperature wear resistant components. It has been widely used in aerospace materials, military industry, and biomedical fields. However, most ceramic materials do not have lubrication functions, especially under dry friction and high temperature conditions, where the friction coefficient and wear rate are relatively high. Therefore, the main strategy for preparing ceramic lubricating composite materials is to introduce single or complex solid lubricating components into the ceramic matrix, in order to form a lubricating film or transfer film during the friction process to achieve anti friction and anti-wear effects. Meanwhile, the inherent brittleness and high wear performance of Al₂O₃ ceramic materials greatly limit their applications in related fields. Therefore, how to improve the mechanical properties of Al₂O₃ ceramics is crucial for their application. In order to clarify the influence of different lubricating phases on the composition, microstructure, and mechanical properties of Al₂O₃ ceramics, three different lubricants, graphite, Mo, and LaF₃, were selected to be added to the Al₂O₃ ceramic lubricating material matrix. A series of Al₂O₃ ceramic lubricating materials were prepared by hot pressing sintering method. Then, the properties of the material were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), BET, and three-point bending methods, and the influence of lubricant type and content on the microstructure and mechanical properties of Al₂O₃ was analyzed. The results indicate that the type and content of lubricants have a significant impact on the microstructure and mechanical properties of the material. As the content of non-metallic lubricating phases increases, the hardness, bending strength, and fracture toughness of the composite material decrease significantly. Adding Mo can significantly improve the strength and toughness of composite materials, mainly because Mo not only makes Al₂O₃ denser, but also plays a role in ductile phase toughening.

Rapid dissipation of shear stress and frictional energy in the matrix of polymer-based self-lubricating composites can improve their friction-reduction and anti-wear performance. In this work, regenerated lignocellulose (RLC) with a flexible architecture was used to assist ball-milling to exfoliate bulk molybdenum disulfide (MoS₂) and introduce it into an epoxy (EP) resin matrix to improve the mechanical and tribological properties of the final products. The abundant functional groups (hydroxyl and aldehyde groups) in RLC undergo an additional reaction with the active hydrogen atoms or epoxy groups in the EP resin, improving the curing performance of the EP matrix and enhancing the flexibility and interfacial strength of the carbon fiber/epoxy (CF/EP) composites. Owing to the simultaneous introduction of rigid MoS₂ nanosheets and flexible plant-fiber constructs in the EP matrix, external stresses can be transferred from the polymer matrix to the reinforcement fibers more efficiently. The tensile strength and toughness of the final products increased by 42.71% and 53.38%, respectively, and the friction coefficient and wear rate decreased by 37.50% and 30.77%, respectively, over those of the CFs/EP@RLC composites. This approach of using RLC to assist in exfoliating MoS₂ nanosheets and building a “flexible & rigid” transition framework in an EP matrix provides a valuable reference for improving the interfacial strength and friction properties of polymer-based self-lubricating composites.

High-entropy boride (HEB) ceramics demonstrate outstanding high-temperature stability, positioning them as promising candidates for reliable performance in extreme environments. However, their inherent limitations lie in their relatively low fracture toughness, coupled with the unclear elucidation of high-temperature tribological behaviors. To address these challenges, high-entropy (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)B₂ ceramics are utilized as the matrix material in the current investigation, whereas hexagonal boron nitride (h-BN) is introduced as a type of toughening and lubricating phase to develop HEB-hBN composite ceramics. The toughening and high-temperature self-lubrication of the composites are achieved by leveraging the high aspect ratio, lamellar microstructure, and interlayer slip characteristics of h-BN. The results indicate that h-BN enhances the fracture toughness of the composite ceramics by nearly 70%, which is attributed to the optimization of the crack growth path through its lamellar microstructure and facilitating crack deflection and bridging mechanisms due to its high aspect ratio. Moreover, through interlayer slip effects, h-BN combines with B₂O₃ and metal oxides generated by high-temperature oxidation, forming a gradient tribofilm in conjunction with other synergistic lubrication mechanisms. This synergistic interaction results in a nearly 40% reduction in the friction coefficient of the composite ceramics, accompanied by an approximately 60% decrease in the wear rate under high-temperature friction conditions at 1000 °C. Under extreme friction environments ranging from 1000 to 1200 °C, the composite ceramics maintain a friction coefficient consistently below 0.30, with the wear rate stably sustained at an order of magnitude of 10⁻⁵ mm³/(N·m).

Ceramic-based lubrication materials are among the best choices for solving high-temperature load-bearing and lubrication problems. However, traditional ceramics achieve self-lubrication by adding lubricating phases, which often leads to significant degradation of mechanical properties, severely limiting their engineering applications. Benefiting from the excellent high-temperature mechanical and lubrication potential of novel high-entropy borides, the present work innovatively proposed a strategy of using high-entropy ceramic components to provide lubrication functions and successfully designed and prepared a novel high-entropy (Ti_0.2V_0.2Nb_0.2Ta_0.2Mo_0.2)B₂ system based on the tribological element design principles. The material achieves synergistic enhancement of both mechanical and tribological performance. Its microhardness, fracture toughness, and flexural strength are 23.8±0.9 GPa, 5.4±0.3 MPa·m^1/2, and 415±17 MPa, respectively. Furthermore, compared with conventional single-phase ceramics, high-entropy (Ti_0.2V_0.2Nb_0.2Ta_0.2Mo_0.2)B₂ with Al₂O₃ balls as the mating partner demonstrates exceptional overall tribological properties across a wide temperature range. Notably, the friction coefficient is as low as 0.12±0.01 at 1000 °C, while the wear rate maintains at a low level ((8.8±0.7)×10⁻⁵ mm³/(N·m)). This outstanding high-temperature tribological performance is attributed primarily to the novel high-temperature solid–liquid synergistic lubrication mechanism generated by liquid-phase B₂O₃ and solid-phase layered MoO₃ and V₂O₅, as well as the excellent high-temperature support provided by the high-entropy (Ti_0.2V_0.2Nb_0.2Ta_0.2Mo_0.2)B₂ substrate.

High-entropy structures in layered compounds, especially transitional metal dichalcogenides (TMDCs), have powered the field with disordered and versatile chemical compositions, showing great potential in various functional applications, including energy storage and catalysis. However, the reported high-entropy phases are mainly 1T phases, 2H phases are rare, and approximately 3R phases are still lacking. Here, phase engineering of high-entropy TMDCs is achieved by tuning the chemical composition of (Mo_0.5W_0.5)_1−x(Nb_0.5Ta_0.5)_xSe_2+δ, 0 ≤ x < 1, and −0.1 ≤ δ ≤ 0.3. A phase diagram is constructed to guide the synthesis of pure 2H/3R phases over a wide composition/entropy range. The increase in VB-group element content and Se overdose facilitated the formation of 3R phases, whereas the opposite occurred for 2H phases. Thermodynamic first-principles calculations evaluate the stability of phases in different polytypes and compositions, matching well with the composition-dependent crystalline habits. Moreover, the optimized thermoelectric performance, with a figure of merit (zT = 0.36@723 K) in 2H phase of x = 0.2, is attributed to the low thermal conductivity (κ) caused by the high-entropy effect, which is one of the highest among (Mo/W)Se₂-based materials. Our work enriches high-entropy TMDCs with versatile polytypes, expanding their potential uses for various fields.

Additive manufacturing technology, by manipulating and emulating inherent multiscale, multi-material, and multifunctional structures found in nature, has created new opportunities for constructing heterogeneous structures associated with special properties and achieving ultra-high mechanical performance and reliability in ceramic composite materials. In this study, we have developed an innovative fabrication method designated as coaxial 3D printing for the synchronous construction of two constituents into ceramic composites with a tooth enamel biomimetic microstructure. Herein, the stiff silicate and flexible epoxy served as a strengthening bridge and toughening layer, respectively. The method differed from the traditional approach of randomly dispersing reinforcing components within a ceramic matrix. It allowed for the direct creation of an internally effective three-dimensional reinforcement network structure in ceramic composites. This process facilitated synergistic deformation and simultaneous enhancement of multiple materials and hierarchical structures. Owing to the uniform distribution of internal stress and effective block of microcrack propagation, the biomimetically structured silicate/epoxy ceramic composite has demonstrated much significant enhancement in mechanical properties, including compressive strength (48.8±3.12 MPa), flexural strength (10.39±1.23 MPa), and flexural toughness (218.7±54.6 kJ/m³), which was 0.5, 2.1, and 47.5 times as high as those of the intrinsic brittle silicate ceramics, respectively. In-situ characterization and multiscale finite element simulation of microstructural evolution during three-point bending deformation further validated multiple-step features of the fracture process (silicate bridge fracture, interface detachment, epoxy extraction, and rupture), which benefited from interpenetrating structural features achieved by coaxial printing to accomplish with the complex propagating routines of the crack deflection in silicate ceramic composites. This coaxial 3D printing method paves the way for tailored toughening−strengthening designs for other brittle engineering ceramic materials.

High-entropy carbides are a nascent group of ceramics that are promising for high-temperature applications due to the combination of good stability, high hardness (H), high strength, and superior creep resistance that they display. Due to high melting points and low lattice diffusion coefficients, however, the high-entropy carbides are usually difficult to consolidate to a nearly full density. To cope with this challenge, herein, binary carbides including TiC, V₈C₇, NbC, Mo₂C, and WC with different carbon stoichiometry were used to prepare dense high-entropy (TiVNbMoW)C_4.375, and the influence of carbon vacancy on formation ability and mechanical properties of carbon-deficient high-entropy (TiVNbMoW)C_4.375 were investigated. Intriguingly, although the starting binary carbides have different crystal structures and carbon stoichiometry, the as-prepared high-entropy material showed a rock-salt structure with a relatively high density (98.1%) and good mechanical properties with hardness of 19.4±0.4 GPa and fracture toughness (K_IC) of 4.02 MPa·m^1/2. More importantly, the high-entropy (TiVNbMoW)C_4.375 exhibited low coefficient of friction (COF) at room temperature (RT) and 800 ℃. Wear rate (W) gradually increased with the temperature rising, which were attributed to the formation of low-hardness oxidation films at high temperatures to aggravate wear. At 800 ℃, lubricating films formed from sufficient oxidation products of V₂O₅ and MoO₃ effectively improved tribological behavior of the high-entropy (TiVNbMoW)C_4.375. Wear mechanisms were mainly abrasive wear resulting from grain pullout and brittle fracture as well as oxidation wear generated from high-temperature reactions. These results are useful as valuable guidance and reference to the synthesis of high-entropy ceramics (HECs) for sliding parts under high-temperature serving conditions.

To explore the application prospects of high-entropy carbide ceramics as wear-resistant parts, a high-entropy (TiVTaMoW)C ceramic with a uniform distribution of elements was prepared via ball milling and subsequent two-step sintering with metal carbides as raw materials. The friction and wear properties of (TiVTaMoW)C ceramic at room temperature and 800 ℃ sliding against Al₂O₃, SiC, and Si₃N₄ balls were investigated, respectively. The results show that (TiVTaMoW)C ceramic exhibits superior tribological properties with low friction coefficients and wear rates at room temperature. Especially for sliding against SiC ball, the friction coefficient and wear rate are (0.38±0.01) and (1.52±0.36)×10^–7 mm³/(N·m). The surface of (TiVTaMoW)C ceramic is severely oxidized during sliding and accompanied by aggravated wear when the temperature is 800 ℃. The wear rates of high-entropy carbide ceramic sliding against all of the friction pair balls can increase to 10^-4 mm³/Nm. The oxidation products of MoO₃ and V₂O₅ with low shear stress characteristics form self-lubricating and transferring films between the friction pairs, which made the friction coefficients maintain the same level as that at room temperature. In addition, SiC friction pair presents better tribological compatibility with (TiVTaMoW)C ceramic with a low friction coefficient and wear rate at room temperature and 800 ℃.