The braking behaviors of Cu-Based powder metallurgy brake pads mated with C/C–SiC disk for high-speed train

Abstract

The improvement of braking systems for the high-speed train is driven by the demand for high & stable coefficient of friction (COF) as well as low wear at high speed. Given to the fading COF and severe wear of powder metallurgy (P/M) pad mated steel disk serving high-speed train in present, C/C–SiC ceramic materials are regarded as a strong candidate for braking disk due to the excellent strength, fracture toughness coupled with relatively low density. The fundamental understanding of the braking behavior at different braking speeds should be clarified for optimal application. In this work, P/M pads and C/C–SiC ceramic disk were prepared, braking tests with the initial braking speeds (IBS) of 15, 22, 30, 37, 46, 55, 59, 64, 69 m/s were conducted, and the surface development, friction & wear behavior were analysed. The COF vs. IBS curve shows a three-stage changing based on the turning points due to the contact patches continuously forming, growing and degrading: it went down and reached a low point with a value of 0.443 at 37 m/s, then increased gradually and reached the maximum 0.486 at 55 m/s, then little fell to 0.460 at 69 m/s. In the great scope of braking speeds, P/M pads mated C/C–SiC ceramic disk showed both high mean friction coefficient of 0.469 and high stability coefficient of 0.908, which are higher than the corresponding values of same P/M pads mated with typical steel disk (0.381 for COF and 0.895 for stability coefficient). Furthermore, at the highest speed tested, the wear rate of the pad mated with the ceramic disk is 0.147 cm3/MJ, far lower than that with steel mate: 0.338 cm3/MJ, showing desired properties for the high-speed train, owing to slight adhesion between ceramic disk and metal matrix of the pad.