Coating cohesion and adhesion - Assessment of stresses in plasma sprayed coatings applied to railway disc brakes

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Coating cohesion and adhesion - Assessment of stresses in plasma sprayed coatings applied to railway disc brakes

Watremez, M. / Guerin, J.D. / Bricout, J.P.

Railway brake disc materials with higher frictional performance and longer durability are needed in order to reach higher train speeds and to reduce maintenance costs. Previous studies have shown that specified combinations of materials, such as plasma sprayed disc coupled with sintered ceramic pads, lead to good behaviour in high-speed train braking simulation as well as in full scale braking conditions. In that case, the coating must be as cohesive as adhesive. A numerical model is developed to obtain stress distribution in a multilayer coating, of several materials with different behaviours. An inverse three-point bending test is used to determine the coating's failure energy. This model is representative of admissible coating stress. Different thermal barriers and friction coatings are then discussed. We intend to define an adhesive or cohesive bond parameter in terms of stress. Adhesion or cohesion performance of selected coatings can be compared with disc thermal stresses in braking situation. Finally, coating limits can be predicted, and disc potential capacities could be improved by disc design variants.