Crystallographic Orientation Dependence of Nanopattern Morphology and Size in Electropolished Polycrystalline and Monocrystalline Aluminum: An EBSD and SEM Study

Electropolishing of aluminum (Al) has been applied to form surface nanopatterns of various morphologies and sizes. However, the effect of crystallographic orientation on nanopattern morphology and size in electropolished Al is unclear. Here, annealed polycrystalline and monocrystalline Al samples were electropolished at 40 V in an electrolyte of perchloric acid, ethanol, butyl cellusolve and water, the correlation between crystallographic orientation and nanopattern morphology and size was firmly established through systematic EBSD and SEM examination. Heterogeneity in nanopattern morphology and nanopattern size is induced by crystallographic anisotropy of grains. Nanopattern morphology and size change gradually for grains and planes oriented with varying misorientation angles against each primary direction [101]//ND, [101]//ND and [111]//ND. The transitions between nanopattern morphologies also occur for grain surface planes with near identical misorientation angles. The surface structure sensitivity of nanopattern morphology and size was firmly established and then qualitatively explained by invoking step-terrace and step-ledge surface structure models and by developing a refined adsorption-diffusion perspective based on a reported theoretical model. The findings reported here contribute significantly to gaining new insights into the crystallographic orientation dependence of nanopattern morphology and nanopattern size in electropolished Al and other metals.