Microstructure and Texture of Electrodeposited Nanocrystalline Nickel in the As-Deposited State and After In-Situ and Ex-Situ Annealing

Abstract

The microstructure and texture characteristics of electrodeposited nanocrystalline nickel have been investigated in the present work. The material has been studied both in an as-received state and after in-situ and ex-situ annealing. The ASTAR automated crystal orientation mapping in a transmission electron microscope complemented by electron backscatter diffraction (EBSD) has been used in the investigation. The as-deposited material consisted of nanograins interspersed with coarser (sub)grain clusters, arranged in large mesoscale colonies and characterized by a dominant 〈001〉 fiber texture aligned with the deposition direction (DD). A large fraction of nanograin/cluster boundaries displayed a low-coincidence site lattice (low Σ) or twin character. The EBSD study confirmed the previously suggested presence of the “cobblestone”-type mesotexture, characterized by a local 〈001〉 fiber axis approximately perpendicular to the hemispherical growth surface of a mesoscale colony. The (sub)grain clusters contained low-angle boundaries and displayed large misorientation gradients; nevertheless, their orientations did not statistically differ from the surrounding nanograins. They did not serve as nuclei for the abnormal grain growth observed during annealing. The 〈001〉//DD to 〈111〉//DD fiber texture transition occurring during annealing did not result from the growth of pre-existing suitably oriented nuclei. Instead, copious twinning occurring along the migration front of the abnormally growing grains appeared to be primarily responsible for the above transition.