Electron Micrographic Digital Image Correlation: Method Optimization and Microstructural banding Case Study

Segregation-induced microstructural banding is commonly encountered in commercial steels, yet its effect on the global mechanical behavior is disputed in the literature due to the difficulty of designing clean control experiments. This work locally compares the deformation of banded phases with unbanded regions in the same microstructure from in-situ electron micrographs analyzed with (optimized) micrographic digital image correlation. To this end, first, the employed electron micrographic digital image correlation (EMDIC) methodology is optimized in terms of its experimental parameters: specimen surface preparation settings, scanning electron microscopy imaging settings (contrast modes, magnification, resolution, and contrast-brightness), and image correlation settings (facet size and facet step size). Subsequently, the strength of the (optimized) EMDIC methodology is demonstrated on a case study on segregation-induced microstructural banding in steel, in which the influence of the banded phase and its morphology is probed by comparing the mechanical behavior of two carefully chosen, extreme cases of banded microstructures: a microstructure containing a continuous, hard band (the martensitic-ferritic system) and a microstructure containing non-continuous, softer bands (the pearlitic-ferritic system). The obtained micro-scale strain fields yield clear insight into the influence of band structure, morphology and band material properties.