Quantitative evolution of tribo-layers in copper based friction materials for high-speed trains operating at 400 km/h equivalent energy density: Ratio of formation to damage

Abstract

The quantitative Evolution of the braking properties and tribo-layer of copper based friction materials (CBFM) at 400 km/h equivalent energy density was investigated. The braking properties of CBFM were determined, with two significant degradations at the 1st and 12th cycles. The ratio of formation to damage of the tribo-layer, t, based on the thickness of the sub-surface of CBFM and wear debris, was defined. The variation of t showed an excellent correlation with the decline in the coefficient of friction. The mechanically mixed layer (MML) deteriorates after the first cycle, evolving into a mixed MML-PDL (plastic deformation layer) structure. The deformed substrate gradually loses hard particles, resulting in a tribo-layer predominantly composed of severely deformed copper, with minimal iron content and numerous defects.