Deformation and chemical evolution during tribology in cementite
Pearlitic steels, which consist of brittle cementite lamella in a ductile ferrite matrix, are commonly used as a structural material due to their capability of being “tailored” in accordance with its engineering application. In tribology, pearlitic components of the rail-wheel system undergo cyclic plastic deformation due to high contact pressures. The severity of plasticity and decomposition of the cementite leads subsequently to the formation of the white etching layer (WEL), which detrimentally affects the operating life of a structure [1,2].
To analyze the extent of plastic deformation of pearlitic steels, we investigate the microstructure evolution under a tribological load that mimics the deformation of a microasperity. In the previous studies, it was shown that both ferrite and cementite deform plastically to a great extent under the wear track . However, bending experiments of cementite cantilevers have shown very limited plasticity and no incremental crack development . In the current study, we conduct single wear track experiments to study the microstructure and chemical evolution in pure cementite under a tribological load.
Wear tracks were observed via scanning electron microscope (SEM) and have revealed typical wear features for plastically deformed materials, i.e., slip markings, wear particles and pile-up. The electron backscatter diffraction (EBSD) of wear tracks showed no grain refinement or orientation gradient inside the wear track. However, during the analysis of the deformed zone via transmission electron microscope (TEM), a nanocrystalline layer, as well as grain twinning, were observed.
The chemical evolution in cementite due to the tribological load was studied with energy dispersive x-ray spectroscopy (EDX), Auger spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that the elemental distribution under the wear track remains homogeneous and cementite does not decompose.
 Weng, Y.: Microstructure evolution of hypereutectoid pearlite steel under rolling-sliding contact loading, Mater. Sci. Eng. A. A655 (2016) 50–59.
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