Design And Tribological Properties Of The Environment-friendly Three-layer Composites

Three-layer composites, a special type of self-lubricating composites, have been widely used in many applications owing to their excellent tribological properties in oilless or poor oil operating conditions. But at present,the high content of lead in the surface compositions of PTFE three-layer composites leads to a great problem of environmental pollution, which can not be ignored. It is a urgent task to develop lead-free or less-lead three-layer composites.PTFE and PEEK were selected as the polymer base of the surface layer, the lead-free composition design was investigated, and the tribological properties of the prepared three-layer composites were studied systematicly. The main conclusions are as follows:1. Considering the significant impact of the composite sintering process on the tribological properties of three-layer composites, the sintering process was studied in detail in this thesis, including sintering temperature, holding time and cooling form. After experimental optimization, we get the best plasticizing sintering process.2. In the lead-free composition design, it is mainly studied the functions of several fillers, which reveals that the function of the same filler maybe different for the different polymer bases.(1) For the lead-free PTFE three-layer composites, the resin filler PI is better than glass fiber or carbon fiber in increasing the wear resistance;the solid lubricant MoS2 is better than graphite in PTFE and its best content is 5%wt; the reinforcement of the thermoplastic polymer PI is better than those of PPS and PEEK and the best content of PI is 20%wt.(2) For the lead-free PEEK three-layer composites, the solid lubricant graphite is better than MoS2 in PTFE and its best content is 5%wt; and adding glass fiber or PTFE into the graphite reinforced PEEK can obviously increase the tribological properties and load carrying capacity of the materials, the effect of the glass fiber on the improvement of the performance is better than that of PTFE,the best contents of glass fiber are 15%wt and 20%wt for oilless and oil lubricating conditions respectively.3. The analysis of wear mechanisms showed that the main wear behaviors of the lead-free PTFE three-layer composites filled with PPS or PEEK or PI are adhesion and micro-cutting. The wear mechanism of the lead-free PEEK three-layer composite without fillers is severe adhesion. The wear mechanisms of the lead-free PEEK three-layer composites filled with PTFE + graphite or glass fiber + graphite are mainly adhesion and micro-cutting. In oil lubricating conditions, the wear behaviors of the PTFE or PEEK three-layer composites are mainly fatigue wear.4. The tribological properties and load carrying capacity of the developed lead-free PEEK three-layer composites in our work are superior to those of the high-quality commercial PTFE three-layer composites. The performances of the developed lead-free PTFE three-layer composites are also better than those of the common commercial PTFE three-layer composites.