Tribology and airborne particle emissions from grey cast iron and WC reinforced laser cladded brake discs
Yezhe Lyu, Francesco Varriale, Vilhelm Malmborg, Martin Ek, Joakim Pagels, Jens Wahlström
Abstract
Laser cladding (LC) is a promising technique to overlay a protective coating on grey cast iron (GCI) brake discs to enhance the wear and corrosion resistance. This study utilized a pin-on-disc tribometer in an aerosol chamber to investigate the tribology and airborne particle emissions from tungsten carbides (WC) reinforced coating overlayed onto GCI substrate through laser cladding. Uncoated GCI brake discs served as reference material, while low-metallic (LM) and non-asbestos organic (NAO) brake pads were used as counterparts. The results indicate that LC coating exhibited slightly higher coefficient of friction and significantly lower wear than uncoated GCI discs. Abrasive wear is the dominant wear mechanism for both uncoated GCI brake discs and LC coatings. LC coatings substantially decreased the particle mass concentrations. All three friction pairs displayed a mass weighted size distribution with a major peak around 2–3 μm. The number size distribution was dominated by a mode below 1 μm. Emissions by number were generally low. Meanwhile, all three friction pairs emitted sheared off and agglomerated particles, with iron being the dominant element. Tungsten was identified in the particles emitted from LC coatings, indicating that the hard coating has a potential to wear off and become airborne particles. • Tribology and emission of WC reinforced laser-cladded (LC) brake disc is studied. • LC disc has slightly lower coefficient of friction than grey cast iron (GCI) disc. • LC disc largely increases the wear resistance of brake disc. • LC coating largely decreases particle mass concentration. • The emitted particles contain sheared off particles and dense agglomerates.