A Comparative Study of Plasma Sprayed Coatings on Railway Brake Discs

Abstract

In the railway context, increasing the number of trains in service relies in the development of new equipment. This objective requires increased peak speeds at the expense of stronger motorisations. The axle loads are thus heavier, especially for the new double-decker trains. These parameters have significant effects on the brake system in terms of size, non-suspended masses, and therefore energies to be dissipated. The constituent materials of the friction brakes of some railway equipment (full non-ventilated steel alloy discs for the TGV, for example) have thus reached their technological limits in terms of energy to be dissipated for fixed mass and size. It is therefore necessary to find more powerful braking devices using new materials. The Laboratoire d'Automatique et de Mécanique Industrielles et Humaines (LAMIH) has therefore decided to focus its research towards high energy full discs. This approach consists of coating the steel discs with low thermal diffusivity friction materials that have very strong and stable mechanical and tribological characteristics at high temperature. Using blown thermal plasma, the LAMIH has already tested reduced scale C38 discs coated with NiCr–Cr₃ C₂ cermet facing an Al₂ TiO₅ pad. Henceforth, studies relate to cobalt or nickel based superalloys obtained by the transferred plasma process with a view to making a reliable coating–substrate bond. Performance is evaluated in terms of friction factor, wear, contact temperature, and reliability.