Speaker
Description
Pearlite is a lamellar composite microstructure that enhances the strength of steel while preserving its ductility. One of the prominent applications of pearlite in tribology is in the rail-wheel system. However, due to high contact pressures, the cyclic plastic deformation leads to the formation of the brittle nanostructured white etching layer (WEL) [1].
The pearlite microstructure transformation is often recreated using severe plastic deformation techniques. Previous studies [2] demonstrated several stages of microstructure evolution, i.e. colonies reorientation, microstructure refinement, cementite breaking and dissolution. In this work, we investigate the microstructure evolution of bulk cementite under tribological load. Thus, the effect of cementite co-deformation with ductile ferrite matrix is excluded.
We perform indentation and wear tests on the bulk cementite sample produced by spark plasma sintering [3]. After testing, scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM) were used to analyze the microstructure transformation under tribological load. Chemical evolution was investigated via energy-dispersive X-ray spectroscopy (EDS), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD).
The macroscale indentation results in brittle fracture whereas wear experiments lead to plasticity in the contact region. TEM investigation of the single-pass wear track reveals the nanocrystalline region with high dislocation density. Below the nanocrystalline region, we observe a transition region with long stacking faults, deformation bands, and dislocation cell formation. The study of chemical evolution does not demonstrate the signs of cementite dissolution to graphite. However, TEM diffraction indicates the phase transformation of cementite into Hägg carbide (Fe5C2).
References
[1] Masoumi, M. et al., Materials Science and Engineering: A 722 (2018)
[2] Hohenwarter, A. et al., Materials Science and Engineering 219 (2017)
[3] Umemoto, M.; et al., Materials Science Forum 426-432 (2003)
| Speaker Country | Germany |
|---|