Size effect of CrFe particles on tribological behavior and airborne particle emissions of copper metal matrix composites

Brake wear particles emitted from vehicles during friction have become an important source of airborne particulate matter (PM) that causes adverse health effects. Particle emissions might be reduced by optimizing the composition of friction materials. Effects of CrFe particle size on tribological behavior and airborne particle emissions of copper metal matrix composites (Cu-MMCs) were investigated using a pin-on-disc tribometer at sliding speeds ranging from 2.5 to 5.0 m/s. The results indicate that the frictional properties, particle emission behavior and worn surface characteristics of Cu-MMCs were strongly influenced by the size of CrFe particles. With decreasing the CrFe particle size, the friction coefficient was relatively stable at 3.8 m/s, decreased gradually at 2.5 m/s, and decreased first then increased at 5.0 m/s. Basically, Cu-MMCs with medium-sized CrFe particles (100–150 mesh) produced the highest levels of particle emissions, followed by Cu-MMCs with large-sized CrFe particles (60–100 mesh), and then Cu-MMCs with small-sized CrFe particles (150–250 mesh) in succession. The level of particle emissions from Cu-MMCs increased substantially with increasing sliding speed. The obtained results were explained considering the evolution of the worn surface characteristics during the friction process.