Tribological behavior of Cu-based powder metallurgy friction materials at harsh braking energy density
The equivalent scale reduction experiments were conducted using the MM-3000 friction and wear testing machine,based on the emergency braking parameters corresponding to 200,340 and 400 km/h respectively in Chinese national standard.The experiments were designed to investigate the tribological behavior of Cu-based powder metallurgy friction materials with cast steel as counter-part at different harsh braking energy densities(157,446 and 616 J/mm2).The results show that at braking energy densities of 157 and 446 J/mm2,the average friction coefficient remains stable at approximately 0.250,indicating a reliable braking performance.In contrast,at a braking energy density of 616 J/mm2,the average friction coefficient of the material rapidly decreases from 0.260 to 0.210,indicating an unacceptable braking effect.Furthermore,as the braking energy density increases,a dramatic evolution of the composition,structure and properties on the surface and tribo-layer is observed.Initially,the thickness of the tribo-layer increases,followed by a decrease,as well as the hardness decreases.Moreover,the wear mechanism turns into severe oxidative wear and peeling wear from plowing and adhesive wear and oxidative wear.
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