Surface patterning for multi-scale strain analysis of in-situ SEM mechanical experiments

Scanning electron microscopy (SEM) enables microstructure characterization at multi-scale, having potential to quantify strain distribution across multiple fields of view (FOVs) and exploring coordinated relationships among the deformations of multi-scale microstructures. Optimizing distribution of multi-scale speckles is crucial for achieving high precision and efficiency in digital image correlation (DIC) computations. In this work, a multi-scale strain measurement method is proposed for in-situ SEM mechanical experiments, which relies on an uncomplicated multi-scale speckle preparation method. Multi-scale speckle preparation can be achieved by the combination of spin-coating and magnetron sputtering. By using micro- and macro-speckle, multi-scale strain calculations can be achieved during the in-situ SEM mechanical loading. The InSn macro-speckle is composed of controllable-sized InSn nanoscale speckles, ensuring that the accuracy of DIC measurements in the microscopic regions are not compromised by the coverage of macro-speckles in the testing region. In regions covered exclusively by SiO2 nano-speckles, in-situ SEM mechanical loading allows for the acquisition of high-resolution DIC (HR-DIC) and electron backscatter diffraction (EBSD) data from the same region and under the same deformation state. Experiments are conducted to illustrate the functionality and utility of the multi-scale speckles. Such experimental analyses offer an opportunity to further explore multi-scale strain heterogeneity in some advanced structural materials and provide reliable experimental verification for material mechanics simulations.