Study Of Wear In A Novel Cu-Based Sintered Alloy For Train Brakes (Influence Of Sintered Temperature)

A novel Cu-based composite frictional train brake material composed of several elements such as Al, SiO2, Fe, graphite, Sn, Mn and MoS2 re-enforced with other elements was treated under Powder Metallurgy (P/M) route. Well prepared powders were hydraulically compacted at 650MPa. The materials were sintered at three different temperatures (850oC, 900oC and 950oC) at a constant pressure. The dry sliding friction and wear characteristics of three different sintering treatment temperatures were investigated and the results were remarkable.The tribological behavior of these materials was analyzed by pad-on-disk tests without lubrication and the coefficient of friction, wear rate and wear number were studied in order to identify the effects of the sintering temperature on the base materials composition. The porosities were found to be very high but were adequate to give the right self lubrication properties and to reduce seizure. It was found that the porosity varies inversely proportional to the increase in sintering temperature. The pores in the sintered material were mainly solid lubricants such as graphite and other low melting elements. This also resulted in poor hardness and mechanical properties, which were compensated by its ability to reduce seizure. Much lower wear frictional coefficient, k and the highest coefficient friction,μwith a high wear number, Wn were obtained, indicating a good wear resistance property of the friction material.Three forms of wear mechanisms were observed during the dry sliding process, namely; delamination wear, plowing wear and abrasive wear. The abrasive wear results in flake or break-away debris. These wear mechanisms were found to be responsible for high wear rates on samples sintered at 850oC and 900oC. Generally, the materials demonstrated excellent brake performance and wear resistance. The average values of friction coefficient under excessive pressure (3.13MPa) dry conditions were 0.336, 0.343, and 0.404, at 850oC, 900oC and 950oC respectively.The results show that the main components of worn surface are graphite, SO2, Fe, Cu and oxides of Fe and Cu (Fe203 and CuO) and AlFe. The worn surfaces were divided into three sections: destructive wear section, medium wear section and low wear section. These wear mechanisms were examined by using SEM and XRD. TALYSURF CLI 1000 was also used to classify the varieties of observed abrasive surfaces. The surfaces observed were also classified into three categories based on the degree of surface destruction during the braking process. These are as follows: smooth abrasive surface (mirror surface and integrated friction film; rough abrasive surface (rough surface); highly abrasive surface (much rough surface) showing more excessive wear than the former.