In the present paper, the influences of high temperature on the tribological properties of phenolic resin graphite (PRG) sliding against tungsten carbide-nickel (WC-Ni) alloy in ambient air were investigated systematically. Results demonstrated that the antifriction behaviors of PRG was sensitive to high temperature and PRG exhibits ultra-low coefficient of friction (CoF) of about 0.01–0.015. The low CoF is attributed to the formation of graphite tribofilms, which shows different formation processes on the contact interface at different temperatures (room temperature, 200, 300 and 400 °C). These findings provide insight into the formation mechanism of graphite tribofilms, and provide an important basis for improving the tribological properties of graphite-based friction materials and manufacturing new graphite for seal applications.

In this study, a novel reciprocating tribometer, in which the frictional pairs were immersed in liquid nitrogen directly, was developed to simulate the cryogenic fluid lubrication. To eliminate the negative influence of extremely low temperature on force sensors, a transfer structure of force-deformation, consisting of cantilever beams and measurement beams, was designed specially. It can transfer the structural deformations caused by the loading force and the friction force from the cryogenic zone to the room-temperature zone. The corresponding measurement principle was discussed in detail, and the linear relationship between the structural deformation and the applied force was verified theoretically. Through static calibration experiments, the fitting relationship between the deformations and the loading/friction force was acquired for the developed tribometer. In final, a preliminary investigation of graphite materials was conducted on the tribometer to compare the room-temperature and cryogenic tribological behaviors.

With the rapid development in additive manufacturing technology, three-dimensional (3D) printing process has been extensively utilized for the prototype manufacturing of industrial components. It is becoming possible and fascinating to directly fabricate surface textures for tribological applications by 3D printing. In this study, a series of polylactic acid (PLA) components with spiral-groove surface textures for the application prospect in the field of mechanical seals were fabricated on a commercially available fused deposition modeling (FDM) 3D printer. The frictional behaviors of the printed components under oil lubrication were investigated on an end-face tribometer. The influence of spiral groove number, groove depth, and printing orientation on friction coefficients was discussed. The test results indicate that the frictional performance of linear-printed component with small groove depth is much better than that of homocentric-printed ones with large groove depth. The minimum average friction coefficient of linear-printed component is about 0.07 while the value is about 0.085 for the homocentric-printed ones. In final, a theoretical simulation based on the Reynolds lubricating regime was conducted to clarify the underlying mechanism of the experimental results, and the numerical results show that the hydrodynamic effect of the linear-printed components is more obvious due to the interaction between the linear printing clearances and the rotation of the counterpart.