Abstract
Gray cast iron (GCI) is a popular automotive brake disc material by virtue of its high melting point as well as excellent heat storage and damping capability. GCI is also attractive because of its good castability and machinability, combined with its cost-effectiveness. Although several lightweight alloys have been explored as alternatives in an attempt to achieve weight reduction, their widespread use has been limited by low melting point and high inherent costs. Therefore, GCI is still the preferred material for brake discs due to its robust performance. However, poor corrosion resistance and excessive wear of brake disc material during service continue to be areas of concern, with the latter leading to brake emissions in the form of dust and particulate matter that have adverse effects on human health. With the exhaust emission norms becoming increasingly stringent, it is important to address the problem of brake disc wear without compromising the braking performance of the material. Surface treatment of GCI brake discs in the form of a suitable coating represents a promising solution to this problem. This paper reviews the different coating technologies and materials that have been traditionally used and examines the prospects of some emergent thermal spray technologies, along with the industrial implications of adopting them for brake disc applications.
Highlights
Brake discs, known as brake rotors, are a crucial part of the automotive braking system which slows down the vehicle by converting kinetic energy into thermal energy, and increases the temperature of the disc friction surfaces
The poor corrosion resistance of Gray cast iron (GCI) leading to brake judder [5,6], high weight contributing to increased fuel consumption [7], and brake wear emissions in the form of brake dust and particulate matter [8,9,10] are some of the major disadvantages of GCI
The limits on these emissions set by the European Commission (EC) and by the Environmental Protection Agency (EPA) are certain to become stricter in the foreseeable future, which will force automotive industries to search for techno-economically viable solutions [29]
Summary
Known as brake rotors, are a crucial part of the automotive braking system which slows down the vehicle by converting kinetic energy into thermal energy, and increases the temperature of the disc friction surfaces. Aluminum MMCs have demonstrated good resistance to corrosion and wear whilst offering significant reduction in weight [3,11] It has issues such as lower melting temperature and higher coefficient of thermal expansion as compared to GCI [12,13,14]. Of specific concern is the fact that approximately 50% of the particles generated from brake wear become airborne, with 80%–98% of them being in the PM10 (particulate matter having diameter of 10 μm or less) range [26,27,28] The limits on these emissions set by the European Commission (EC) and by the Environmental Protection Agency (EPA) are certain to become stricter in the foreseeable future, which will force automotive industries to search for techno-economically viable solutions [29]. Such restrictive environmental laws will increasingly limit the use of this technology on a commercial scale and motivate development of other techno-economically viable alternatives
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