Tribo-performance assessment of milled fly ash brake friction composites

The milled fly ash (MFA) was attained by mechanical ball milling of raw fly ash (RFA) and was characterized for changes in particles morphology, size, and specific surface area (SSA). The RFA and MFA, varying in wt% from 20 to 35, were exclusively used for composite fabrication using compression molding machine. The milled fly ash composite (MFC) specimens were assessed for the tribo-performance in comparison with raw fly ash composite (RFC) and commercial truck brake composite (CTBC) specimens under the loads ranging from 125 to 200 N at 3.3 and 5 m/s of sliding velocity. The characterization study showed that the glassy and spherical RFA particles of average size 86 mu m changed to rough and irregular size of 15 mu m, after ball milling. The SSA per unit bulk volume was found to increase from 138.2 to 1009 m(2)/m(3). The tribo-study revealed that the fly ash milling significantly improved the friction coefficient of MFC specimens, especially at 35 wt% of MFA, as compared to RFC and CTBC specimens. The increase in fly ash content (raw as well as milled) to 35 wt% greatly increased the specific wear rate (SWR) at both the sliding velocities. The worn surfaces of RFC specimens were found to be more damaged than the MFC specimens as revealed from SEM results. The appreciable frictional characteristics of MFC specimens encourage the use of MFA in brake friction composites; however, the changes in the friction formulation are required from SWR point of view.