Three-dimensional EBSD characterization of thermo-mechanical fatigue crack morphology in compacted graphite iron

• Crystallographic features of a thermo-mechanical fatigue (TMF) crack were studied.
• Wide-field 3D EBSD is used to characterize the TMF crack morphology.
• Data processing was applied on a large length scale of the order of millimeters.
• Graphite density in the fracture plane is much higher than any other random plane.
• It is revealed that crack growth is enhanced by the presence of graphite particles.

In cylinder heads made of compacted graphitic iron (CGI), heating and cooling cycles can lead to localized cracking due to thermo-mechanical fatigue (TMF). To meticulously characterize the complex crack path morphology of CGI under TMF condition, in relation to microstructural features and to find out how and by which mechanisms the cracks predominantly develop, three-dimensional electron back scattering diffraction (EBSD) was employed. Based on the precise quantitative microstructural analysis, it is found that graphite particles not only play a crucial role in the crack initiation, but also are of primary significance for crack propagation, i.e. crack growth is enhanced by the presence of graphite particles. Furthermore, the density of graphite particles on the fracture plane is more than double as high as in any other arbitrary plane of the structure. The obtained results did not indicate a particular crystallographic preference of fracture plane, i.e. the crystal plane parallel to the fracture plane was nearly of random orientation.