Wear Mechanism/microstructure Relationships for Laser Processed Cast Iron (Erosion, Abrasion, Martensite, Transformation)
Chen, Chung-Hsin
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https://hdl.handle.net/2142/71830
Description
Title
Wear Mechanism/microstructure Relationships for Laser Processed Cast Iron (Erosion, Abrasion, Martensite, Transformation)
Author(s)
Chen, Chung-Hsin
Issue Date
1986
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Metallurgy
Abstract
The objectives of this research are to (1) investigate the potential for CO(,2) laser processing to produce novel, non-equilibrium surface microstructures in cast iron and (2) investigate the basic wear mechanisms of these non-equilibrium microstructures. Three kinds of microstructures can be produced by this laser processing. A very hard feathery microstructure ((TURN)100 HV), a "soft" dendritic microstructure ((TURN)550 HV) and a mixed microstructure. A modified Ashby's model allows accurate estimation of the melt depth, the cooling rate etc., at the solid/liquid interface. The original and laser processed microstructures and hardnesses are correlated with the laser processing parameters and with the specimen erosion and abrasion rates. The wear resistances of laser processed samples are much improved due to the elimination of graphite nodules, the increased hardnesses and the greatly refined microstructures, as well as the austenite to martensite transformation in the dendritic microstructure sample. Of special interest is this austenite to martensite transformation. In a liquid nitrogen thermal treated (-196(DEGREES)C) sample, only bct high carbon martensite is present. In a mechanically deformed sample, both bct martensite and hcp (epsilon)-martensite are observed. Generally, in the subsurface of a deformed sample, the area surrounding interdendritic cementite has a higher density of martensite plates. The frequent intersection of martensite plates induced by deformation in this area causes the initiation of microcracks. Further propagation of these microcracks with continued deformation is believed to be the origin of wear particle generation.
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