The auto industry is facing challenges from new regulations including the brake particulate emission standard. Various coating and surface treatment technologies (e.g., laser cladding, thermal spraying, and FNC) have been investigated with hope for better wear resistance of brake discs and thus a lower particle emission as a result. Plasma Electrolytic Aluminating (PEA) process has also been proposed to produce alumina hard coatings on cast iron brake discs. In this work, the compatibility of different brake pads vs. alumina-coated discs was particularly studied. Alumina-coated discs were prepared and then slightly polished to two different surface finish. After that, the discs were cut into small coupons for pin-on-disc tribotests, where the low-steel and NAO (non-asbestos organic) brake pads were used as counterparts. The wear tracks were analyzed using Scanning Electron Microscopy (SEM). The results show that the alumina coatings with dimpled surface morphology would promote the formation of transfer bedding layers (TBL), leading to alternation of brake discs from abrasive wear to adhesive friction. A lower surface roughness of the alumina coatings resulted in a better coverage with an even transfer layer on the friction surface. The NAO brake pad had a higher tendency to transfer its friction materials to the coated disc surfaces, while the low-steel pad was also able to form a TBL which was thinner but still with a good coverage. As a result, the low-steel brake pad exhibited a lower weight loss when it slid against the alumina-coated disc samples regardless the high or low coating surface roughness. The coated brake disc samples, on the other hand, show a minimum wear or even weight gains. Although the coated brake discs have presented a very good wear resistance in this study, the brake pads can however be formulated better to have a lower wear rate and therefore the entire brake system would be able to meet the upcoming non-exhaust emission regulations.
Prof. Dr. Xueyuan Nie, Professor, University of Windsor; Mr. Yinting Liu, M.A.Sc. graduate student, University of Windsor; Ms. Ran Cai, Ph.D. graduate student, University of Windsor; Mrs. Jingzeng Zhang, Researcher Associate, University of Windsor