Direct comparison of nanoscale plasticity in single and bi-crystal tensile tests extracted from a zinc coating

Zinc coatings are widely used for corrosion protection of steel products and are therefore crucial for their longevity. However, how commonly used mildly alloyed zinc coatings deform at the individual grain level and how the plasticity mechanism transitions towards more complex behaviour due to kinematic constraints originating from the microstructure remains unclear. We address these research questions by performing in-situ microscale tensile tests on four single crystal orientations and two combinations thereof, as a bi-crystal, resulting in nanoscale deformation fields that are analysed in detail through a novel slip identification method to yield quantitative slip system activity fields, also supported by post-mortem electron backscatter diffraction analysis. We discover that combining the two single-crystal orientations within a bi-crystal specimen leads to a transition from pyramidal II to the rarely observed pyramidal I slip. In contrast, the basal slip is abundantly present. Furthermore, we provide a relation between critical resolved shear stress (CRSS) and the size of the specimen for the basal slip system based on single-arm source theory, which clarifies important features of the deformation behaviour of microscale zinc films and can be used to guide the design of new coatings.