(V) Correlative light, electron and in-situ Raman imaging of modern and historic railway tracks, linking wear and corrosion behavior to microstructure and composition
Mechanical and corrosion damage in worn 1930s and 1950s rails were compared against unused but environmentally corroded modern rail. Multimodal correlative microscopy and in situ Raman spectroscopy allowed qualitative evaluation of deformation and corrosion mechanisms, against differences in metallurgy and microstructure such as inclusion content, grain size, crystal phase, decarburization and wear.
In-situ correlative Raman imaging was carried out in a field emission scanning electron microscope, correlated with multiple contrast methods in light microscopy, high resolution secondary electron imaging and energy-dispersive x-ray spectroscopy. Light microscopy, EDS and Raman were used together to characterize the microstructure, oxides and inclusions in each rail, localized to specific regions of mechanical damage. This provided a correlation between regions of high wear and deformation with the corrosion species and the contemporary composition of the rail steels. The integration of a Raman microscope in the chamber of the SEM uniquely allows rapid correlative workflows and overlay of spectra with optical and electron imaging.