Friction performance of carbon/silicon carbide ceramic composite brakes in ambient air and water spray environment

Abstract

Citation: BIAN, G. and WU, H., 2015 AbstractWe have examined friction performance, friction surface structure and chemistry of a carbon/silicon carbide ceramic brake disc tested against an organic pad in air, and water sprayenvironment. An average friction coefficient of 0.52 and 0.4 for a braking stop is achieved after bedding in air for a composite disc comprising 53.1% and 17.7% SiC/Si, respectively. It is identified that 100% SiC/Si and ~50% C f /C regions contribute the friction measurement.Tested in water spray, both brakes show a substantial fall of friction coefficient to a level <0.1.Evidences are provided for the existence of hydrodynamic friction. Friction transfer materials removal, SiC region polishing, and lower real contact pressure reinforce hydrodynamic process that a ceramic composite brake can experience.

Friction surface structure of a Cf/C–SiC composite brake disc after bedding testing on a full-scale dynamometer

“…on a laboratory-scale dynamometer. These results have already been reported in previous pblications 13,15,16,17 . The study was later extended to the friction surface of a composite brake disc tested on a car 18,19 , which is compared to that tested on laboratory-scale dynamometer.…”

“…There are two distinguishable layers inside the TM: a top layer with a thickness of ~100 nm and an underneath region. The former one is called friction layer (FL) in this paper, the same layer as found before 13,17 , and the later one called underneath layer (UL). By applying an aperture with a size of 200 nm, a representative selected area diffraction pattern for the FL and UL is shown in Figure 5 (b) and (c), respectively.…”

“…SiC is a much stronger ceramic phase than C f and PyC, but surface fracture can be developed by an abrasion process 29,30 . Most recent research 13,17 shows that a repeated abrasion during braking promotes the development of lattice defects such as dislocations and twins on the contact surface of SiC, and the accumulation of dislocations/twins on the surface leads to a stress concentration to initiate microcracking inside SiC crystallites. The liaison of these microcracks on the surface eventually leads to chipping off, or dislodging of a SiC region from the surface.…”

“…Even so, some desired friction performance has not yet achieved to a desired level, for example, fast bedding in (running in), consistent friction performance under all operating conditions, and suitability for wet environment 13 . Friciton performance of a brake should be determined by the carbon ceramic composite and coupled friction material, but it is the friction surface developed during braking that is in charge to directly dictate its friction performance.…”

“…In ref. 13, two types of C f /C-SiC were studied on the impact of fraction of each constituent on friction performance by testing them against same organic pad. The carbon ceramic composite used for the brake disc of brake-H is a similar material used in this study.…”