Comparison of Friction and Wear Behavior Between C/C, C/C-SiC and Metallic Composite Materials

The search for suitable friction materials for high-speed train is an attractive but difficult problem. In recent years, a variety of different novel friction materials were fabricated to meet the aims of high loads and speeds under ambient environment. Carbon fiber-reinforced carbon composites (C/C), carbon fiber-reinforced silicon carbide composites (C/C-SiC) and metallic composites fabricated by powder metallurgy are three excellent materials among them. Here a comparison of these three different materials working as brake pads, coupled with high-density C/C-SiC brake disk, was described. All the experiments were conducted using the same procedure with increasing initial braking speed (the rotation speed of brake disk at the beginning of braking process) from 30 to 59 m/s and constant load of 1.25 MPa, simulating the real working condition of highspeed train. The coefficient of friction (COF) and wear rates of three materials were compared and analyzed. During experiments, the COF of metallic and C/C pads remains nearly constant at 0.31 and 0.22, respectively, with increasing braking speed, while that of C/C-SiC exhibits a parabola. These different trends of COF may be attributed to the distinctive forming processes of friction film on the top of contact surfaces. Meanwhile, the wear rates of metallic composites increase rapidly from 683 to 1803 mm(3)/MJ with initial braking speed, while C/C-SiC presents the highest wear loss of 1887 mm(3)/MJ at 49 m/s and lowest value of 315 mm(3)/MJ at 59 m/s. Interestingly, the wear rate of C/C composites, due to the appropriate bonding strength of matrix/fiber and relatively high shear stress, decreases from 3698 to 903 mm(3)/MJ with increasing initial braking speed, which does not consist with pre-existing paper. Thus, metallic pads presented the lowest wear rates at lower speed (<49 m/s) but the highest at high speed, while C/C-SiC composite pads showed the greatest wear resistance at high speed. This investigation of three different friction materials will enhance our understanding of these friction materials and benefit the selection and safe application of high-speed train friction materials.