In-situ observation of transfer film formation and evolution for the fabric composite lubricated spherical plain bearing at cryogenic and wide temperature range

The time evolution and temperature dependence of friction along with transfer film morphology and composition for the polytetrafluoroethylene (PTFE) fabric composite lubricated spherical plain bearing was unraveled through a home-made cryogenic tribotester integrating in-situ Fourier Transform Infrared (FTIR) microscopy. Specifically, the temperature dependence of which shows two regions divided by 190 K, and PTFE plays a crucial role on the lubrication of the fabric composite. Thin and uniform transfer film generally forms at 323 K, however, with decreasing temperature, friction increases and transfer film formation is suppressed, which is attributed to the freezing molecular chain movement and inhibition of molecular reorientation of PTFE. After reaching the highest value around 190 K, friction coefficient slightly decreases with further decreasing temperature due to the brittle delamination of PTFE fragments and formation of less-oriented and patch-like uneven transfer film. The transition temperature around 190 K is closely related to the gamma relaxation of PTFE owing to totally restricted mobility of PTFE molecules. Furthermore, inner ring with a surface roughness of 200-300 nm is found to be beneficial to materials transfer and lower friction by increasing plastic flow of PTFE lubricating material at cryogenic temperatures.