Impact of Ceramic Coatings on Grey Cast Iron Rotors on Friction Performance of Automotive Brakes

Abstract

Increasing concerns towards non-exhaust emissions from friction brake engagements has led researchers to explore coatings for brake rotors with the aim of improving their corrosion and wear resistance. The development of regenerative braking systems also adds to the thrive towards a better environment through increasing power conservation and decreasing friction interactions by ~ 5-20% reduction in the friction brake engagements compared with traditional friction braking systems. This research focuses on friction performance of a typical ASTM A48 Class 30 gray cast iron brake rotor and an Original Equipment Manufacturer (OEM) Ford F150 brake rotor, both coated with a newly patented ceramic coating, tested against commercially available low metallic (LM) aftermarket brake pads. The friction performance was evaluated according to ISO/SAE J2522 test procedure carried out using a scaled down bench top wear tester (Bruker Tribolab). Subsequently, thorough material characterization was performed on the bulk and friction surfaces using polarized light microscopy (Nikon Microphot FX), scanning electron microscopy (FEI Quanta FEG 450), energy dispersive x-ray microanalysis (Oxford detector, Inca Systems), surface topography (NPFLEX 3D Optical Microscopy), density (analytical balance and Archimedes principle) and Shore D hardness (PHT-980 Durometer). The results indicated significantly lower wear on both the pads and rotors when coated rotors were used compared to the tests with identical pads and uncoated rotors. Compared with uncoated rotors, approximately 17% decrease in average friction level was recorded when identical brake pads were tested against coated rotors. This behavior was related to the nature of the ceramic layer deposited on the rotor and its capacity to contribute to formation of specific friction layers on surfaces of coated rotors and pads. The analysis of worn surfaces and wear particulates demonstrated different topography and chemical composition, respectively, for the coated rotor/pad pairs compared with those of uncoated rotor/pad pairs. The findings in this work introduce a promising new generation of coatings for gray cast iron rotors and ignite further studies to further assess the coatings in accordance with commonly used industry standards and friction brake pads.