The Performance of Semi-Metallic Friction Materials for Passenger Cars

In this work, a semi-metallic friction material for passenger cars was evaluated for mechanical wear by pressing the material against a rotating pearlitic gray cast iron brake disc. In each test, the sample was subjected to four different braking times (3, 6, 9, and 12 minutes) and four applied loads (200, 400, 600 and 800 N). The rotating velocity of the disc was kept constant throughout the friction tests at 750 rpm. After each test, the morphological changes on the surface and subsurface of the material were observed using Scanning Electron Microscopy (SEM). The following characteristics were observed: (i) the surface temperature increased with braking time and after reaching a maximum value, eventually arrived at a steady state, (ii) the friction coefficient increased at the early stages of braking, then decreased with braking time and thereafter reached steady state, and (iii) the wear volume increased linearly when the applied load was below 200 N and/or braking time was below 3 minutes or both, thereafter the volume increased exponentially. Microstructural examinations showed that the wear mechanism transisted with increase in braking times as well as applied loads. This phenomenon also resulted in changes of the wear behaviour.