The Tribological Performance For The Thermoplastic Polyimide Composites

The friction and wear behavior are the universal phenomenon for the moving parts in contact. Nowadays, the polymers especially for the high performance polymers have found more and more tribological applications and are increasingly displacing metals and or ceramics in various fields for their excellent properties. Recently the aircraft, car, electronics and military industries require more advanced materials, which have better tribological properties with higher load-carrying capacity, chemical stability and higher temperature resistance. PI, as one of the most excellent engineering plastics, is well known for their marked thermal-stability, excellent mechanical properties and resistance to most of solvents, and becoming one of best candidates for high temperature tribological applications. Many studies are focused on the improvements in mechanical and tribological properties of PI filled with solid lubricants and fiber-reinforcer. The PTFE and short-cut carbon fiber (CF) had been considered to fill with a new thermoplastic PI and the tribological and mechanical properties for those composites were investigated in this thesis. The friction and wear mechanism and the limit PV values for the PI composites were also investigated.In order to determine the tribological properties of the PI composites, the tribological apparatus was firstly improved in this thesis. The friction coefficient and worming surface temperature of material could be measured on-line. And the tribological and mechanical properties for a novel aromatic polyimide modified by PTFE were demonstrated, and the worn surface morphology was also analyzed by means of SEM. The results indicated that the tribological performance of the composite could be obviously improved compared with the pure resin. The friction coefficient and specific wear rate decreased in low PTFE contents, and then increased with further increase of PTFE content, both of them seemed to be minimums at 30% PTFE content. The main wear mechanism of the pure polyimide was fatigue and adhesive wear for the composite due to the decrease of mechanical properties.The mechanical and tribological properties of composites reinforced by short-cut carbon fiber were further investigated in this thesis. The results showed that the compression strength, flexural strength and tensile textile strength of composites increased with increase of CF content. At the same time its tribological properties were also improved, the friction coefficient increased firstly and then reached at a constant level, and the specific wear rates decreased in low CF content and then increased with the further increase of CF content. Both of them seemed to be minimums at 10% CF content, the minimum friction and wear coefficient were 0.12 and 1.83×10-8cm3(N-1(m-1, respectively. The main wear mechanism of composites in low CF content was adhesive wear, and abrasive wear for the high CF content from the worm surface analyzed by SEM.For the composite of a novel PI modified by PTFE, the measurement method of limit PV value was researched. The effects of the Heat Deforming Temperature, sliding velocity and load on the limit PV value were discussed. The results showed that the composites would be deformed and peeled off as the load and sliding velocity reached a limit value. Meanwhile, the friction coefficient and temperature would intensively increase, which indicated to be the limit PV. The most important factor of limit PV value was depended on the Heat Deforming Temperature of material. The limit PV value under low velocity and high load was higher than that of under high velocity and low load due to lower friction coefficient.