Microstructural and Tribological Evaluation of Brake Disc Refurbishing Using Fe-Based Coating via Directed Energy Deposition

Hossein Rajaei,Matteo Perini,Giovanni Straffelini,Stefano Gialanella,Cinzia Menapace,Sasan Amirabdollahian

doi:10.3390/met12030465

Abstract

In this paper, the refurbishing of worn-out brake discs by coating with powder via direct energy deposition (DED) is evaluated. A medium carbon steel powder was used to coat cast-iron discs. Deposition of this steel was carried out directly on the disc surface or, alternatively, after a previous deposition of a buffer layer made of stainless steel. It was seen that the use of a buffer layer ensured a good coating adhesion, despite the formation of cast microstructures at the interfaces between the disc and the two different coatings (buffer and outer layer). Coated discs were tested against two different Cu-free commercial friction materials to evaluate their tribological properties. Very similar friction coefficients, specific wear rates, and total emissions were measured for both friction materials sliding against the coated disc. These tribological data are slightly higher with respect to those obtained in the case of an uncoated disc, suggesting that improvement of the top coating composition and surface finishing is necessary in order to achieve better performances.

Highlights

Due to its low cost of manufacture, good castability, and excellent tribological and mechanical qualities, gray cast iron (GCI) is a popular casting material, widely employed in mass production, including the manufacturing of brake discs [1,2]
The results showed that the coated disc had a higher friction coefficient compared to that of the uncoated GCI
The laser surface engineering of the Fe-based materials involves the alloying and hardening of the surface using a laser beam, for the purpose of improving the surface properties [11,22–25]. The goal of this project was to restore worn-out brake discs by means of a direct energy deposition (DED) process, using a stainless steel as the buffer layer to reduce flaws and hot cracking, before adding a top layer of steel that is devoid of hazardous elements such as Co, Ni, Cu, and W

Summary

Introduction

Due to its low cost of manufacture, good castability, and excellent tribological and mechanical qualities, gray cast iron (GCI) is a popular casting material, widely employed in mass production, including the manufacturing of brake discs [1,2]. Exhaust brake rotors are currently managed mostly through remelting, with just a small percentage ending up in landfills. Both methods dissipate a significant amount of energy, with a significant associated CO2 footprint [3]. Another important environmental issue with disc brakes is the formation of airborne wear particles that contribute to particulate matter (PM) emissions. As regulations and exhaust emission standards become more and more rigorous, it is becoming more critical than ever to solve the issue of brake disc wear without compromising the materials’ braking performance. The design and deposition of an appropriate coating on the surface of GCI brake discs could be a viable solution to both of these problems [1]

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Conclusion