Effect of graphite type on the contact plateaus and friction properties of copper-based friction material for high-speed railway train

Abstract Copper-based friction materials containing the same graphite concentrations but varied proportion of granular graphite to flake graphite were prepared by powder metallurgy for high-speed railway trains. The friction coefficient and specific wear rate were tested on pin on disc machine. The results showed that the addition of appropriate granular graphite can improve the magnitude and stability of friction coefficient and help to form the secondary plateaus on friction surface. However, excessive addition of granular graphite led to a significant decrease in friction coefficient. The flake graphite had better lubricity but promoted the occurrence of delamination due to its weak strength. Statistical analysis revealed that the specific wear rate was negatively linear correlated with the graphite coverage area on the friction surface. In addition, there was a critical plateau coverage on friction surface, above which the specific wear rate can be effectively reduced. Comprehensive evaluation of the magnitude and stability of the friction coefficient as well as wear rate, the ratio of 5 wt% granular graphite to 5 wt% flake graphite is the most suitable for high performance copper-based friction material.