EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Digital Image Correlation (DIC) performed on in-situ Scanning Electron Microscopy (SEM) data provides detailed identification and analysis of micromechanical deformation mechanisms, such as crystallographic slip, grain boundary sliding, etc. By analyzing full-field displacement and/or strain maps, quantitative data, on e.g. slip activity, can be obtained for polycrystalline materials, which has been demonstrated mostly on rather coarse grained materials. Yet, engineering metals typically have very fine grains or phase distributions, which often consist of sub-micrometer-sized features, such as martensite substructures. To understand the plasticity and damage mechanisms at these scales, and to allow direct comparison to (crystal plasticity) simulations, there is a strong need for robust, large strain measurements at spatial resolutions far below the micrometer, that can be traced back to the microstructure. A crucial requirement for proper DIC analysis is a high-quality speckle pattern that provides enough contrast at the scale of interest for DIC to track. Therefore, in this work, we explore the potential of a recently developed patterning methodology in which a low-melting-temperature InSn alloy is deposited through Physical Vapor Deposition in so-called ‘island growth’ mode [Hoefnagels et al.,Strain 2019]. This yields a high-quality and robust DIC pattern which is scalable down to ~10 nm sized speckles, allowing the measurement of strain fields at spatial resolutions below 50 nm. Moreover, we introduce an align framework in which strains are carefully overlaid on top of multi-modal microstructure maps to allow for straightforward interpretation of the strain fields. We explore a case study in which in-situ SEM-DIC micro-tensile testing is performed on ferrite-martensite interface specimens. Through the resulting microstructure-correlated strain fields, compatibility of several plastic deformation mechanisms is investigated, such as ferrite and martensite crystallographic slip and martensite substructure boundary sliding.