High-speed braking properties of Cu-based powder metallurgy brake pads

Friction coefficients of the Cu-based powder metallurgical brake pads decline due to the high temperature during the high-speed braking, which will directly affect the train braking effectiveness. The 1:1 high-speed braking tests of Cu-based powder metallurgical brake pads were carried out under the different speeds, and the friction materials and abrasive texture after the tests were analyzed. The results show that, the metal matrix on the surface of friction materials melts due to the high temperature under the braking speeds of 350 km·h⁻¹ and 380 km·h⁻¹, decreases the shear resistance of the micro bumps on the friction surface, and causes the decline of friction coefficient. The metal oxide films formed on the friction surface reduce the wear, resulting in the further decline of friction coefficient. The friction surface lost the stable lubricant film when the graphite is oxidized under the high temperature generated by 380 km·h⁻¹ braking, and the wear loss increases significantly due to the adhesive wear and material transfer behavior.