Effect of Graphite and Bronze Fillers on PTFE Tribological Behavior: A Commercial Materials Evaluation

This work presents a tribological evaluation of the influence of graphite and bronze fillers in two commercial composites in a dry sliding pin-on-disc test at the same contact severity ( parameter) and four testing conditions (varying both normal force and sliding velocity). Both fillers, in comparison to pure PTFE, significantly affected the coefficient of friction (COF) and the mass loss. The sliding distance required to reach steady-state for COF was statistically equal for all three materials. The COF experienced a relevant influence of both normal force and sliding velocity. The graphite filler acted as a solid lubricant and exhibited reductions in COF (similar to 27% on average) and in mass loss (similar to 4.2 times lower on average). The bronze filler, on the other hand, had a COF increase of up to 5% for conditions with lower normal force but showed a significant reduction on the specific mass loss (similar to 5.3 times lower on average). Due to its higher thermal conductivity, the composite filled with graphite presented lower tribosystem temperatures in thermography evaluations. Good agreement of the temperature data was found considering a model that proposes the rate of heat generated by friction. With respect to wear of the composites, evidence of adhesion (transfer films to the counterface) and abrasive (microploughing and microcutting) wear mechanisms was found, in addition to the identification of preferential wear.