Characterization of ultrafine particles from hardfacing coated brake rotors

Yezhe Lyu, Ankur Sinha, Ulf Olofsson, Stefano Gialanella, Jens Wahlström

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish
Pages (from-to)125-140
Issue number1
Early online date2022
Publication statusPublished - 2023

Bibliographical note

Funding Information:
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.

Funding Information:
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).

Publisher Copyright:
© 2021, The author(s).

Subject classification (UKÄ)

  • Tribology


  • brake
  • high-velocity oxygen fuel
  • laser cladding
  • particle morphology
  • particle size distribution
  • ultrafine particle


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