Date of Award
Doctor of Philosophy
Friction interaction between brake materials see a rise in temperatures of over 1000 oC contributing to thermal fade of brakes and deterioration/cracking of rotors. Various microstructural features like graphite, ferrite and pearlite could influence the mechanical and thermal properties and related friction performance of the brake materials. Even more relevant impact on properties and friction performance of rotors can be expected after coatings or surface treatments. The primary purpose of this research is to identify the impact of microstructure and surface treatment on properties and friction performance of four types of pearlitic gray cast irons. The C30, C20 and FC150 rotors were surface treated by bombarding with heavy ions which diffused into cast iron and created a coating with different chemistry and properties when compared to the “non-treated” rotors. Complete chemical and material characterization of the brake rotors using optical emission spectrometer (OES), carbon-sulfur combustion analyzer, polarized light microscopy, density (analytical balance and Archimedes principle), Brinell hardness tester, laser flash apparatus, scanning electron microscopy, and energy dispersive X-ray microanalysis. The pearlitic gray cast iron rotors are typified by the presence of graphite, carbides, and inclusions in an almost fully pearlitic matrix with a minimum amount (2-4 vol.%) of “free” ferrite. Graphite can be further classified based on its morphology. The investigated cast irons contained two different graphite types: type VII-E5 for the F150 OEM rotor, and type VII-C5 characteristic for the ASTM A48 classes C30 and C20, as well as the “Japanese” JIS G5501 FC150 rotors. It was identified from the initial curve fitting models that the observed microstructural differences in individual cast iron types are responsible for the observed mechanical (density – decreases with increasing ferrite and decreasing pearlite contents; hardness – decreases with increasing ferrite contents) and thermal properties (increase with increasing ferrite and pearlite contents), and friction performance (increases with increasing ferrite and decreasing graphite contents) of the studied rotors. The applied surface treatment also contributed to the modification of the mechanical and thermal properties, as well as friction performance of the studied rotors. However, there were not enough statistically relevant models developed from the generated data, which could identify the combined influence of various microstructural features observed and applied surface treatment over the properties and friction performance of the studied rotors.
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