Tribological Study On PTW/PTFE Composite

Tribology is a crossed and marginal ology. It is related to physical chemistry, material science, mathematics, mechanics, thermodynamics and et al. Tribology belong to surface science because friction occur on the contacted surface, and has three relative sections: friction, wear and lubrication. Because the frame and performance are programmable, polymers composites are the perfect choice as self-lubrication materials. Human beings have not understood the friction mechanism of polymer composite because of the complexity of frame and the multiplex of performance.In this thesis, the friction, wear, mechanical and rigidity behavior and the relationship among these behaviors of polytetrafluoroethylene (PTFE) filled with potassium titanate whiskers (PTW) has been studied.PTW could increase the rigidity of composite in a certain extent. The composite was the most rigid one when the PTW content was 15 wt. %.The impact strength and tensile strength was improved obviously. The two types of strength changed with the content of PTW went all the way. The composite had the highest impact strength and tensile strength with the PTW content was 15 wt. %.Wear rate of PTW/PTFE composite decrease dramatically with PTW content increasing from 1 to 20 wt%, and then increase slightly with PTW content from 20 to 40 wt%. The PTFE composite reinforced with 20 wt% PTW has the best wear resistant, which is over 1000 times larger than pure PTFE. The friction coefficient decreased with the content of PTW because PTW can reduce the directed contact between PTFE and counter-face. The image of abrasive dust and the worn surface have been investigated. These observations show that the PTW has the ability to reduce wear by preventing the destruction of PTFE's band structure.In this thesis the friction and wear characters have been compared among PTW/PTFE, carbon fiber (CF)/PTFE, glass fiber (GF)/PTFE. The results showed that CF, GF, PTW all could improved the friction and wear characters of PTFE, and PTWwas the best. The dominance of PTW could be the tiniest size, which could present the maximum surface area on the surface of samples, reduced the directed contact between PTFE and counter-face, and then reduced the friction coefficient and wear rate.The rudimental characters of a material lie on its molecule structure. Especially, the mechanical, chemical and thermal characters of polymer material lie on their molecule arrange. Such as PTFE, whose degree of crystallization, the form of crystal and the distribution of crystal all can affect the characters. So the interaction between materials could affect the characters of composite. The crystal of PTFE composite and relationship between the degree of crystallization and the wear behavior was analyzed based on the interaction between PTW and PTFE in this thesis.The results indicate that the degree of crystallization and the integrality of crystal of PTFE composite was remarkable increased with PTW content increasing due to the ability of heterogeneous nucleation of PTW. The degree of crystallization at first decreased as PTW content increased from 0 to 30 wt%, and then decreased slightly from 30 to 40 wt%. The composite with 30 wt% PTW had the highest degree of crystallization which was 20 % higher than pure PTFE. These effects were helpful to improve the rigidity, mechanical properties and wear properties.The unitary character of a multiphase system is contributed by all components. The contribution of each component is different. The friction and wear character of several multiphase systems based on PTFE polymer were researched in our work. The results indicated that PHBA could improve the friction and wear properties of PTFE remarkable. The friction coefficient of composite with 20 wt. % PHBA was the lowest one. The composite with 30 wt. % PHBA had the best wear properties.Some other filler were filled to the PHBA/PTFE system, which can improve the wear property. In our work the system contain 20 wt. % PHBA, 5 wt. % CF and 2 wt. % PTW had the best wear properties which was 20 times than PHBA/PTFE system.Some other filler were filled to the PHBA/PTFE system to be multiphase system. In our researching work the friction coefficient of two multiphase systems presented a type of special periodicity. One multiphase system contained 20 wt. % PHBA, 5 wt.% CF, 2 wt. % PTW and PTFE, the other system contained 20 wt. % PHBA, 5 wt. % CF, 2 wt. % PTW, 2 wt. % graphite and PTFE. The special periodicity could be caused by the transfer film. With the test, the multiphase system could form a special transfer film on the counter face, but the transfer film was unstable and could be destroyed quickly. The transfer film was formed and destroyed continually in the friction process, which caused the periodicity of friction coefficient.