Synthesis and characterization of nanocrystalline alloys in the binary Ni-Co system/

Abstract

Nanocrystalline Ni-Co alloys were synthesized using pulsed electrodeposition from a Watts-type bath, and the various plating parameters were systematically varied to examine their effect on the composition, quality, and structure of the resulting deposits. Increasing the pH of the plating bath and/or the average plating current density increased the Ni content of the deposits, but both of these parameters exhibited rather narrow processing windows for the preparation of high-quality deposits. The addition of saccharin during plating was observed both to reduce the crystallographic texture of the Ni-Co alloys and to refine the grain structure. Owing to the low stacking fault energy of Co, many of the alloy deposits exhibited a large density of nanoscale twins. The unique dual-scale grain and nano-twin structure found here caused apparent discrepancies in the grain size measured by XRD and by other microscopy techniques, and also resulted in unique trends in hardness. This thesis lays the groundwork for future tailoring of nanostructured alloys to explore how twins and stacking faults influence their strength and ductility.