The Synergistic Effect of Cr and CrFe Particles on the Braking Behavior of Cu-Based Powder Metallurgy Brake Pads

Different Cu-based brake pads applied in high-speed railway trains were fabricated by the co-addition of Cr and CrFe particles, and the influence of the Cr/CrFe ratio on the tribological behavior of the powder metallurgy brake pads were studied by a reduced scale testing apparatus with the pad-on-disc configuration under various braking speeds. The results indicated that the Cu-based brake pad containing 6 wt% Cr and 4 wt% CrFe exhibited the highest and the most stable friction coefficient as well as the lowest wear loss when the braking speed was higher than 300 km/h. Moreover, a new reasonable explanation is provided for the effect of Cr and CrFe particles during the braking process. The excellent braking properties are attributed to the synergistic effect of Cr and CrFe on promoting the formation and stabilization of a tribofilm. Cr particles, which have high reactivity with Fe and O, act as a steady source of fine oxides in the tribofilm, and CrFe particles bear the load and strengthen the subsurface in the position near the friction surface. It is clear that the application of an appropriate ratio between Cr and CrFe can develop Cu-based brake pads suitable for more serious braking conditions.