Tribological behavior and wear particle emission influenced by surface conditions of cast iron discs

Abstract

Hard coatings can be applied to a traditional cast iron brake disc to increase wear resistance and thus reduce brake disc particle emission. An alumina coating prepared through a modified plasma electrolytic oxidation (PEO) process also shows a promise in wear reduction for automotive brake disc. The aim of the work was further to study effect of the alumina coating surface conditions on tribological behavior and wear particle emission of the cast iron brake disc using a pin-on-disc (PoD) tribotester combined with an airborne particle emission measurement system. The testing sample surface conditions included uncoated and alumina-coated cast iron disc surfaces with different surface roughness finish. The counterpart pins were machined from a commercially available brake pad, called a low-met (LM) pad. After the tests, the friction transfer layers and emitted particles were analysed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The results showed that the coating surface roughness significantly influenced the bedding-in process and coverage of transfer layers, which led to noticeable difference in coefficients of friction (COF), wear weight loss, and particle number concentrations and size distributions. Compared with the uncoated disc, the coated discs were able to considerably reduce the wear loss of the discs, particle number concentrations, and metal pickup in the emitted particles. A smooth surface coating condition can be utilized to also reduce the pad wear and thus its emission, which would further benefit environment and human health.