The role of constituents contained in water-based friction modifiers for top-of-rail application

•Effects of water-based FMs were investigated using a ball-on-disc tribometer.•Content of binding agent seems to be a crucial parameter for substance behaviour.•Large amount of substance does not necessarily lead to the critically low adhesion.•Performance of substance is greatly affected by evaporation of base medium.•Water-based substances are able to reduce wear and avoid scoring.

Top-of-rail friction modifiers (FMs) represent an up-to-date approach to managing adhesion in the wheel-rail interface. The aim of this study was to investigate the role of typical water-based FM constituents in terms of adhesion and film formation. The ball-on-disc apparatus was employed to reach a rolling-sliding contact. The friction behaviour of various complex substances with different compositions was investigated in terms of adhesion and wear. The results showed that less complex substances, e.g. free of particles for friction modification, can provide required adhesion. Moreover, adhesion was not markedly decreased when the contact was overdosed. The performance of water-based substance/FM is greatly affected by evaporation of water. Surface analyses showed that substances are able to reduce wear and surface damage.