Brake discs for passenger cars are dominantly made of gray-cast iron, which owns many very positive characteristics. Those brake discs have a very good thermo-mechanical resistance, show convenient tribological behavior, can be machined easily and are very reasonable in terms of costs. However, one of their major drawback is the proneness to corrosion. Corrosion leads then to an unattractive appearance of the friction ring, but more important tribology and mechanical strength can be affected in a very negative way. Especially the use case of battery electric cars (BEV) is expected to become a severe issue for standard gray-cast iron discs. One very promising countermeasure idea is a hard-metal coating of the friction ring. Even if this concept can be already found in the market, many open questions still exist – the authors intend to address some them. In a first part, the tribological behavior is investigated by the use of a sophisticated brake dynamometer. This includes the friction performance in terms of level and trend of coefficient of friction during a sophisticated test cycle, as well as the wear behavior is examined. Afterwards, some corrosion and also delamination testing is analyzed to determine the mechanical robustness of the coating concept. The idea is to show how resistant the coating is to the onset of water and salt water. Finally, some physical and chemical analyses of emitted particles are introduced. For this item, a brake particle emission measurement setup was applied and by the use of a cascade impactor several filters were charged in dependency of different particle sizes. Afterwards, samples were prepared to determine particles and agglomeration by the use of SEM and TEM.
Sebastian Gramstat, AUDI AG, Germany; Robert Waninger, Bertram Reinhold, Heino Sieber, , Panayotis Dimopoulos Eggenschwiler, Empa-Swiss Federal Laboratories for Materials Science and Technology, Switzerland Empa-Swiss Federal Laboratories for Materials Science and Technology, Switzerland