Synergistic effects of the ingredients of brake friction materials on friction and wear: A case study on phenolic resin and potassium titanate

Tribological properties of the brake friction material including straight phenolic resin with different molecular weighs (Mw), and potassium titanate with different morphologies (platelet and whisker), were investigated. Results showed that the friction coefficient and wear rate were strongly affected by the contact plateaus on the friction material surface. At low temperatures, before the thermal decomposition of the resin, the friction materials with high-Mw resin and platy potassium titanate yielded improved friction and wear resistance characteristics, which were attributed to the large plateaus on the sliding surface. On the other hand, at temperatures higher than the thermal decomposition temperature, the friction materials comprising high-Mw resin and potassium titanate whisker yielded higher friction levels and lower wear rates. These changes were supported by increased activation energies and the facilitation of secondary contact plateaus by potassium titanate reinforcements. The presence of the contact plateaus also affected the size distribution of the wear debris. At temperatures lower than the thermal decomposition temperature, high-Mw resin produced larger wear debris, whereas friction materials with potassium titanate whisker produced larger wear particles at higher temperatures. These findings suggest that it is possible to tailor brake emissions by considering the synergistic effects of the constituent ingredients.