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.

The tribological properties of self-lubricating composites are influenced by many variables and complex mechanisms. Data-driven methods, including machine learning (ML) algorithms, can yield a better comprehensive understanding of complex problems under the influence of multiple parameters, typically for how tribological performances and material properties correlate. Correlation of friction coefficients and wear rates of copper/aluminum-graphite (Cu/Al-graphite) self-lubricating composites with their inherent material properties (composition, lubricant content, particle size, processing process, and interfacial bonding strength) and the variables related to the testing method (normal load, sliding speed, and sliding distance) were analyzed using traditional approaches, followed by modeling and prediction of tribological properties through five different ML algorithms, namely support vector machine (SVM), K-Nearest neighbor (KNN), random forest (RF), eXtreme gradient boosting (XGBoost), and least-squares boosting (LSBoost), based on the tribology experimental data. Results demonstrated that ML models could satisfactorily predict friction coefficient and wear rate from the material properties and testing method variables data. Herein, the LSBoost model based on the integrated learning algorithm presented the best prediction performance for friction coefficients and wear rates, with R² of 0.9219 and 0.9243, respectively. Feature importance analysis also revealed that the content of graphite and the hardness of the matrix have the greatest influence on the friction coefficients, and the normal load, the content of graphite, and the hardness of the matrix influence the wear rates the most.

The high strength and toughness of natural materials are mainly determined by a combination of mechanisms operating at different length scales, which can be used as a strategy to reduce the intrinsic brittleness of ceramics. Inspired by the architectures of bamboo, the polycrystalline cubic boron nitride/hexagonal boron nitride (PcBN/hBN) fibrous monolithic ceramics with a long fiber arrangement structure was constructed with PcBN fiber cells and hBN cell boundaries, and its crack resistance responses and tribological performances were investigated. The composite ceramic failed in a non-brittle manner with the rising resistance curve (R-curve) behavior, which was attributed to multiscale crack effects in the hierarchical architecture. The maximum crack growth toughness was extremely high (approximately 21 MPa·m^1/2), corresponding to a 270% increase over the crack initiation toughness. Excellent fracture resistance could be retained even above 1000 ℃. Moreover, the composite ceramic exhibited low and stable friction coefficients (approximately 0.33) when paired with a Si₃N₄ pin at high temperature (1000 ℃), owing to the lubrication function of hBN cell boundaries with weak van der Waals forces and a small amount of liquid B₂O₃ produced. As a result, a synergistic improvement of mechanical and tribological properties at high temperature (1000 ℃) was realized by combining bionic structure and tribological design. It provides important theoretical and technical support for expanding the application of self-lubricating composite ceramics in harsh environments.

Cubic boron nitride (cBN) with high hardness, thermal conductivity, wear resistance, and chemical inertness has become the most promising abrasive and machining material. Due to the difficulty of fabricating pure cBN body, generally, some binders are incorporated among cBN particles to prepare polycrystalline cubic boron nitride (PcBN). Hence, the binders play a critical factor to the performances of PcBN composites. In this study, the PcBN composites with three binder systems containing ceramic and metal phases were fabricated by spark plasma sintering (SPS) from 1400 to 1700 ℃. The sintering behaviors and mechanical properties of the composites were investigated. Results show that the effect of binder formulas on mechanical properties mainly related to the compactness, mechanical performances, and thermal expansion coefficient of binder phases, which affect the carrying capacity of the composites and the bonding strength between binder phases and cBN particles. The PcBN composite with SiAlON phase as binder presented optimal flexural strength (465±29 MPa) and fracture toughness (5.62±0.37 MPa·m^1/2), attributing to the synergistic effect similar to transgranular and intergranular fractures. Meanwhile, the excellent mechanical properties can be maintained a comparable level when the temperature even rises to 800 ℃. Due to the weak bonding strength and high porosity, the PcBN composites with Al₂O₃-ZrO₂(3Y) and Al-Ti binder systems exhibited inferior mechanical properties. The possible mechanisms to explain these results were also analyzed.