Research and Simulation Analysis of Tribological Performance of Porous Oil-Storage Polyimide at High Temperature

In this work, a cold pressing-hot sintering method was used to prepare porous polyimide. The thermal stability and tribological performance of pure polyimide (PI), interface lubricated polyimide (PI-Oil), porous polyimide (P-PI), and porous oil-storage polyimide (P-PI-Oil) were compared and investigated within the temperature range of 25 to 250 ℃. The thermal stability of the materials was evaluated using TGA. The results indicated that PI and P-PI had a good thermal stability, and the thermal decomposition temperature exceeded 500 ℃. The addition of benzyl silicone oil reduced the decomposition temperature of P-PI-Oil. Tribological results demonstrated that the friction coefficients of P-PI-Oil and PI-Oil was lower than that of PI and P-PI. Under dry friction conditions, the coefficient of friction was higher. The highest friction coefficient of PI at 100 ℃ was approximately 0.58, while the highest friction coefficient of P-PI at room temperature was approximately 0.54. The introduction of lubricating oil significantly reduced the friction coefficient of polyimide. The friction coefficient of PI-Oil was generally around 0.10, while the friction coefficient of P-PI-Oil remained stable at around 0.05. At 100 ℃, P-PI-Oil had the lowest friction coefficient with a minimum value of 0.04. Under room temperature conditions, the wear rate of the four materials was relatively small, maintaining at around 1.08×10⁻⁵ mm³/(N·m). The wear rate increased with the increase in temperature, especially for P-PI-Oil, where the wear rate sharply increased to 1.50×10⁻⁴mm³/(N·m) at 250 ℃. Additionally, due to the decrease in thermal mechanical properties, the material underwent deformation. On the other hand, PI had a wear rate of approximately 4.88×10⁻⁵ mm³/(N·m) at 250 ℃. This was because the high-temperature environment reduced the mechanical strength of the material due to its porous structure, resulting in a decrease in interface load-bearing capacity and wear resistance. SEM results demonstrated that the wear of PI and P-PI was primarily dominated by abrasive wear and fatigue wear, while PI-Oil and P-PI-Oil were mainly influenced by adhesive wear and abrasive wear. The tribological mechanism indicated that during the sliding process, materials underwent frictional oxidation and chelation reactions with the metal counterpart, promoting the formation of transfer films. The formation of transfer films during the friction process prevented direct contact between the two friction interfaces, which had a significant impact on the tribological performance of polyimide. The addition of lubricating oil altered the structure of the transfer film, resulting in a uniformly covered transfer film on the mating surfaces. XPS results indicated that the frictional oxidation and chelation reactions that occurred during the friction process enhanced the load-bearing capacity of the transfer film, making the structure of the transfer film more stable. Simulation results demonstrated that the addition of lubricating oil effectively reduced stress concentration and contact shear forces within the material, resulting in a more stable internal structure and reducing wear and damage caused by friction and stress concentration, thereby extending the material's service life.