Pin-on-disc for investigating the tribological properties of brake pad friction materials produced by positive molding

Brake pad specimens were fabricated using powder technology combined with positive molding to investigate the tribological performance of copper free friction materials compared with conventional copper based formulations. Six compositions were prepared by varying mica iron oxide (MIO) and steel fiber contents, alongside one copper reference sample. Tribological evaluation was conducted using a pin on disc (POD) method under controlled braking cycles, while worn surfaces were analyzed via SEM/EDXS to elucidate microstructural mechanisms governing fade–recovery behavior. This study examines the fade–recovery behavior, disc temperature response, and worn surface microstructure of low steel brake pads incorporating varying proportions of steel fibers, copper/brass, and MIO. Fade and recovery rates (%FR and %RR) were used as key indicators of performance, with higher values reflecting superior stability. Among the tested samples, C۹B۶ exhibited the highest fade resistance and recovery, attributed to the high thermal conductivity of copper and zinc and the formation of a stable lubricating friction film. Increasing MIO content initially improved fade resistance up to ۶ wt.% (M۶S۹), but excessive levels reduced stability due to weakened platelet support and premature wear particle detachment. Recovery rates generally exceeded fade rates, with M۰S۱۵ and M۳S۱۲ showing the most favorable values, though excessive MIO (۱۲ wt.%) caused a marked decline. Disc temperature analysis confirmed that copper–brass pads dissipated heat more effectively, while higher MIO content led to elevated temperatures and accelerated degradation of heat sensitive constituents. Microstructural observations revealed that steel fibers stabilized wear debris and promoted dense secondary platelets, whereas excessive MIO favored larger, less stable type II platelets. Overall, the performance ranking was C۹B۶ > M۶S۹ > M۳S۱۲ > M۰S۱۵ > M۹S۶ > M۱۲S۳, underscoring the importance of balanced composition for optimal tribological behavior.