Braking performance of Fe-based and Cu-based powder metallurgy pads paired with C/C-SiC disc on full-scale dynamometer

Abstract

： In this study, the friction performance of copper-based (Cu-PM) and iron-based (Fe-PM) powder metallurgy pad was systematically compared and analyzed by performing braking test paired with C/C-SiC disc on full-scale flywheel brake dynamometer, including coefficient of friction (COF), wear rate (Wr) and worn surface under dry and wet tests. The test procedure simulated the braking conditions on high-speed trains with initial brake speed (IBS) from 50 km/h to 200 km/h, as well as under various brake clamping force (FB). During dry tests, both pads exhibited high levels of COF, the mean value of average COF (µm) for Cu-PM pad was 0.371, which was slightly higher than that of 0.358 from Fe-PM pad. The stability of µm over the IBS ranged from 68% to 82% for Cu-PM pad under different FB, while it was from 82% to 85% for Fe-PM pad. However, during the wet tests, the mean value of µm dropped to 0.207 for Cu-PM pad, and with the minimum µm of 0.062, whereas they were 0.344 and 0.188 for Fe-PM pad, respectively, showing a significant difference in the friction performance between two pads. Additionally, the Wr of Cu-PM pad was 0.110 cm3/MJ during dry tests, which was 17.3% lower than that of 0.133 cm3/MJ observed for Fe-PM pad. After the brake test with Cu-PM pad, the friction film primarily covered the Si/SiC-rich region of the disc, effectively inhibiting the ploughing of SiC hard asperities onto the pad surface. However, the friction film predominantly covered the fiber-rich region of the disc after the test with Fe-PM pad, the exposing of hard Si/SiC-rich asperities would continuously plowing the pad during braking and resulted in furrows on the surface of Fe-PM pad. In terms of wear mechanisms, adhesion wear was the primary mechanism on the contact surfaces of Cu-PM pad and C/C-SiC disc, while abrasion dominated the interaction between Fe-PM pad and C/C-SiC disc. This study provides valuable insights for the application of C/C-SiC brake disc on trains.