Abstract
Automotive brake rotors are commonly made from gray cast iron (GCI). During usage, brake rotors are gradually worn off and periodically replaced. Currently, replaced brake rotors are mostly remelted to produce brand-new cast iron products, resulting in a relatively high energy consumption and carbon footprint into the environment. In addition, automotive brakes emit airborne particles. Some of the emitted particles are categorized as ultrafine, which are sized below 100 nm, leading to a series of health and environmental impacts. In this study, two surface treatment techniques are applied, i.e., high-velocity oxygen fuel (HVOF) and laser cladding (LC), to overlay wear-resistant coatings on conventional GCI brake rotors in order to refurbish the replaced GCI brake rotor and to avoid the remelting procedure. The two coating materials are evaluated in terms of their coefficient of friction (CoF), wear, and ultrafine particle emissions, by comparing them with a typical GCI brake rotor. The results show that the CoF of the HVOF disc is higher than those of the GCI and LC discs. Meanwhile, HVOF disc has the lowest wear rate but results in the highest wear rate on the mating brake pad material. The LC disc yields a similar wear rate as the GCI disc. The ultrafine particles from the GCI and LC discs appeared primarily in round, chunky, and flake shapes. The HVOF disc emits unique needle-shaped particles. In the ultrafine particle range, the GCI and HVOF discs generate particles that are primarily below 100 nm in the running-in period and 200 nm in the steady state. Meanwhile, the LC disc emitted particles that are primarily ∼200 nm in the entire test run.
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Acknowledgements
The authors are grateful for the financial support from FORMAS: Swedish Research Council for Sustainable Development (No. 2020–02302) (Nescup project). The research also received funding from European Union’s Horizon 2020 research and innovation programme (No. 954377) (nPETS project).
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Yezhe LYU. He is an assistant professor in Machine Elements at Lund University (LTH), Sweden. He obtained his Ph. D. degree at KTH Royal Institute of Technology, Sweden, in 2018, with a thesis of Railway Open System Tribology. He has been a visiting scientist at Technical University of Darmstadt, Germany within “Future Talent” Programme. He has been awarded the Postdoctoral Fellowship by Japanese Society for the Promotion of Science (JSPS) to visit Keio University. He is the winner of Hakon Hansson Prize of 2021. He is leading and participating several national and international research projects with special research interests on airborne particle emissions in general wear processes and their health and environmental impacts.
Ankur SINHA. He completed his M.S. degree in materials engineering. Currently, he is pursuing his doctoral studies at the Department of Industrial Engineering, University of Trento, Italy. His Ph.D. work aims at developing transmission electron microscopy (TEM) based investigation protocols for fine and ultrafine particulate matter, starting from the non-exhaust vehicular emissions.
Ulf OLOFSSON. He is a professor in tribology at the KTH Royal Institute of Technology, Sweden, since 2006. He received his Ph.D. degree in 1996 on a thesis on wear as failure mechanism in boundary lubricated rolling bearings. He has been a visiting scientist at Sheffield University, UK and at BREMBO SPA Italy. His main research interests include interfaces and especially simulation and prediction of friction and wear, mainly applied to problems in mechanical, automotive, and railway engineering. New research interests include friction modifiers in rolling sliding contacts and joints, airborne particles from wear processes such as in disc brakes and railway wheel to rail contacts.
Stefano GIALANELLA. He is an associate professor in materials science and technology. His more recent research interests concern phase transformations, high temperature oxidation and wear of structural alloys and materials for brake systems, nanostructured materials and their microscopy characterization, archaeometry, and cultural heritage issues. On these and related subjects, he teaches courses for undergraduate and graduate students of the Departments of Industrial Engineering and Humanities in the University of Trento, Italy.
Jens WAHLSTRÖM. He is a chaired professor in Machine Elements at Lund University (LTH), Sweden. His research is focused on the tribological performance and non-exhaust emissions from machine elements (such as brakes, gears, and wheel-to-rail) in road and rail vehicles. He has designed and applied both experimental and simulation approaches in his research. He is, and has been, working in several national and international interdisciplinary research projects.
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Lyu, Y., Sinha, A., Olofsson, U. et al. Characterization of ultrafine particles from hardfacing coated brake rotors. Friction 11, 125–140 (2023). https://doi.org/10.1007/s40544-021-0585-2
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DOI: https://doi.org/10.1007/s40544-021-0585-2