A Robust Patterning Technique for Electron Microscopy-Based Digital Image Correlation at Sub-Micron Resolutions

Digital image correlation of scanning electron microscope images is a powerful technique for measuring full-field deformation at microstructural length scales. A major challenge in applying this technique is the fabrication of speckle patterns small enough to facilitate full-field measurements with high spatial resolutions and at high magnifications. Current approaches are inconsistent, damaging to the substrate, or highly substrate dependent, which requires researchers to recalibrate or develop new patterning approaches when changing materials systems. Here, multi-layered Au, Ti, and Ag sputtered coatings are reconfigured in a NaCl solution to quickly form DIC-appropriate speckle patterns. Our proposed technique is shown to be substrate independent, as demonstrated on neat epoxy, Ti-6Al-4V titanium alloy, and tetragonal zirconia polycrystal samples, and allows for controllable particle distributions by varying the sputtered Ag layer thickness. Patterns produced by the proposed technique enable the use of correlation window (subset) sizes smaller than 1 μm, small enough to capture highly localized deformation gradients at material discontinuities areas. Capabilities of this method in characterizing highly heterogeneous deformation conditions at sub-micron scales are demonstrated by measuring localized deformations in a single fiber model composite system.