Wear mechanisms alteration at braking interface through atmosphere modification

Abstract This paper relates to changes in the third body arrangement of a squealing pad-disc interface, triggered by altering the tribological circuit of particles. A sealed chamber placed around a friction experiment, allows to run-in the parts with dry air atmosphere, and then to switch from air to argon. Observations of surfaces worn in dry air match the literature. The major part of the surfaces is covered by a third-body layer containing oxidized metal, in the form of powder or compacted plateaus, the rest of the surfaces being native, non-oxidized material from the first bodies. The squealing sound is steady and has a well-defined spectral content. Two stages of sliding of 400 s each are then performed with changed atmosphere. The squealing sound becomes sporadic and its spectral content changes. On the pad's surface, the coverage of compacted third-body plateaus reduces, while more non-oxidized metal appears. A specific pattern of plateaus appears on top of graphite particles. The evolution of the vibrational behavior and of the third-body layer are both gradual and have not reached a steady state when the experiment is stopped. We propose a scenario involving a change in the balance between the source flows and the wear flow as an explanation of the observed tribological changes.