The Role of Copper on the Friction and Wear Performance of Automotive Brake Friction Materials

Copper has been regarded as one of the indispensable ingredients in the brake friction materials since it provides high thermal diffusivity at the sliding interface. However, the recent regulations against environmentally hazardous ingredients limit the use of copper in the commercial friction material and much effort has been made for the alternatives. In this work, the role of the cuprous ingredients such as copper fiber, copper powder, cupric oxide (CuO), and copper sulfide (CuS) are studied using the friction materials based on commercial formulations. The investigation was performed using a full inertial brake dynamometer and 1/5 scale dynamometer for brake performance and wear test. Results showed that the cuprous ingredients played a crucial role in maintaining the stable friction film at the friction interface, resulting in improved friction stability and reduced aggressiveness against counter disk. In particular, the addition of copper fiber or copper sulfide contributed to improved friction stability during effectiveness test. The test result also showed that the friction material containing 10 wt.% of cupric oxide exhibited better fade resistance without showing an abrupt decrease of friction coefficient during brake performance and wear tests. The addition of copper fiber showed better wear resistance compared to the friction material with cupric oxide, on the other hand, the increase of copper fiber showed an adverse effect in the wear resistance of the friction materials during wear tests up to 400°C.