Applying the latest microscopy techniques to studyphase transformations at rail surfaces

Abstract

Cementite decomposition leading to the formation of the whiteetching layer (WEL) on the surface of rail tracks was investigated byelectron energy loss spectroscopy (EELS) in the TEM and by threedimensionalatom probe (3D-AP). It is shown that the carbonconcentration inside cementite laths undergoing severe plasticdeformation in the transition zone between the pearlitic substrateand the WEL remains stoechiometric. However there exists a boundarylayer at the ferrite/cementite interface where the carbon compositiondecreases, indicating that decomposition is an interfacialphenomenon. Carbon atoms diffuse into the ferrite and segregatealong structural defects leading to a heterogeneous supersaturatedcomposition in the white etching layer.