Hengzhong Fan

Surface Engineering Design of Alumina/Molybdenum Fibrous Monolithic Ceramic to Achieve Excellent Lubrication in a High Vacuum Environment

Al2O3/Mo fibrous monolithic ceramics are potential candidates for space applications because of their excellent mechanical properties and low density. This study aims at achieving low friction and long life of this material in a high vacuum environment. Three-dimensional composite-lubricating layers were fabricated by considering texture pattern as storage dimples and MoS2 synthesized via hydrothermal method as lubricant. The tribological properties were studied sliding against Si3N4 ceramic and GCr15 bearing steel balls under high vacuum condition. Results showed that the lubricating properties of the Al2O3/Mo fibrous monolithic ceramics were improved greatly by the micro-texture and MoS2 solid lubricant; the friction coefficients were as low as approximately 0.08 and 0.04, respectively, when Si3N4 ceramic and GCr15 bearing steel balls acted as the pairing materials. It was also demonstrated that the low friction coefficient can be realized with various normal loads and sliding speeds, indicating the composite-lubricating layers have good adaptation of working conditions. This excellent performance of the material is mainly because of MoS2 stored in dimples can be easily dragged onto the friction surface to form lubricating and transferring films during the friction process. This work is an extension of studies that were previously published in Tribology Letters journal.

Surface Engineering Design of Alumina-Matrix Composites

The three-dimensional lubricating layer on a ceramic surface realizes the integration of the structure and lubricating function in ceramic materials, which can achieve outstanding lubricating properties and maintain the excellent mechanical properties of ceramics, solving the special lubrication and wear failure in mechanical systems under extreme conditions (e.g., corrosive environment and wide-temperature range condition). In this chapter, two kinds of surface-lubricating structural-laminated ceramics with high reliability were designed and prepared based on experiment research and theoretical simulation. These ceramics can achieve stable and effective lubrication in a water environment and wide-temperature range condition. These materials are Al2O3/Ni- and Al2O3/Mo-laminated composites suitable for use in a water environment and in wide-temperature range conditions, respectively. The relation between the surface microstructure of the prepared materials and their properties (mechanical and tribological) was investigated. Results indicated that the integration of the structure and lubricating function of the ceramic composites is realized through the bionic, surface microstructure, and three-dimensional self-lubricating design of the materials, further improving their lubricating and practical properties. Factors that can influence the tribological behavior and wear failure of the above materials were proposed through the systematic study of the tribological behavior under different environments and test conditions, as well as the relation among the structure, composition, and properties of these two kinds of materials. In addition, theoretical models of the relation between the structural parameters and performance of the materials were built. These methods provided theories and technologies for the preparation and application of high performance lubricating materials that can be used in corrosive and wide-temperature range environments.